The Garden Shed

A Community Newsletter published by the Piedmont Master Gardeners

January 2024-Vol.10,No.1

 

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  Soil Compaction

The Ornamental Garden in January

Rain Gardens

The Edible Garden in January

For comments, questions or suggested topics for future Garden Shed articles contact us at: garden-shed@piedmontmastergardeners.org.

If you have specific gardening questions or need help to solve a gardening problem, our Horticultural Help Desk is a free community resource and can be contacted at 434-872-4583 or by email: albemarlevcehelpdesk@gmail.com.

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We are members of the Piedmont Master Gardeners, which simply means we have all been trained to share the scientific expertise of Virginia Tech and the Virginia Cooperative Extension Service. More important, we are your friends and neighbors with a passion for gardening – and learning more about it. MORE

Table of Contents

Tasks and Tips

The Ornamental Garden in January

By Pat Chadwick

Keep tabs on newly-planted trees and shrubs to make sure they are getting enough moisture over the winter months.

In the Ornamental Garden

Rain Gardens

By Melissa King

Intro to rain gardens and their function, plus how to create one on your own property

Tasks and Tips

The Edible Garden in January

By Ralph Morini

January is a great time to review the past year's garden results and plan to apply your learning to improve next year's success.

Upcoming Events

Upcoming Events

By Cathy Caldwell

Learn about pruning and starting seeds

Feature

Soil Compaction

By Chris Stroupe

And what you can do about it

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The Edible Garden in January

• January 9, 2024
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Winter is a great time to relax while starting to think about the upcoming spring gardening year. While we rest physically from the effort of last season, we can think about how to improve our practices environmentally and horticulturally. Here are some ideas that can help move us in that direction:

Most gardeners know about the advisability of keeping a garden journal, but I suspect many of us are careless about maintaining them. Keeping an accurate journal is a great New Year’s resolution. Journals can include any and all information that can help build gardening success, including:

• A garden sketch to track specific crop locations, through spring, summer and fall plantings. Use the information to plan crop rotation to reduce pest and disease issues.
• Organizing companion planting and intercropping practices to build soil health and help reduce weed incursions. Note the dates when specific diseases and pests arrive and/or depart, on which plants, to let you know when to take action to manage damage.

Vegetable IPM Guide, Penn State Extension. Photo: R Morini

• When investigating seed or plant purchases, look for varieties that resist the problem diseases and pests that you have identified.
• Identify and record pests and ways to combat them. A good resource is the Penn State Extension publication Vegetable Integrated Pest Management With an Emphasis on Biocontrol.
• The new seed catalogs are out now, both online and hard copy. It is worth reviewing a few different providers to compare selection and prices while deciding what to plant in your precious garden space. Look for seed and plant varieties with good pest resistance. Maybe choose to grow something you’ve never grown before, which is a good learning experience, if not plain old fun. Review The Garden Shed article Using Seed Packet Information to Help the Garden Grow for help interpreting pest and disease resistance information.
• If you are thinking of adding small fruits to the garden, review the VCE publication Small Fruit in the Home Garden for helpful advice.
• Read and record best gardening practices. Study Integrated Pest Management (IPM) as a way to reduce chemical use. Learn about regenerative gardening practices that focus on naturally building healthy soils as the basis for healthy, nutritious crops.
• Review ways to add pollinator habitat to your landscape to create a healthy insect population and use beneficial insects to help keep pests under control.

If you are looking for some reference books to advance your horticultural education, check out The Garden Shed articles Books Every Gardener Should Have and/or New Gardening Books.

Learning and recording new skills over the winter and putting them into practice in the coming season is a great way to become a better and happier gardener.

Hands-on Tasks

• While decomposition slows down as temperatures drop below 50 degrees F, it is a good idea to collect materials over the winter to start new compost batches in the spring. Stock your pile or compost bin with leaves, preferably chopped. If you need more “brown” (carbon-rich) materials for your batch, save newspapers, boxes and household paper, not contaminated with plastic tape, coatings or cleaning fluids, tear them up and add them in. Add kitchen fruit and vegetable scraps to the pile during the winter and rotate the pile every once in a while. In the spring, when green materials like grass clippings are available, add them in to get to a volume ratio of about twice as many browns as greens, moisten everything so it is wet but not dripping, rotate it once or twice a week and you’ll have beautiful compost in time for planting summer vegetables in May. For detailed advice on home composting, review The Garden Shed article Backyard Composting with Practical Tips from the Pros.

Simple seed starting setup. Photo: R Morini

• If you want to begin starting seedlings indoors this winter now is the time to acquire equipment and plan the process. Check out The Garden Shed article Starting Seeds Indoors for detailed guidance from an experienced Master Gardener.
• If you have older seeds that may have outlived their viability, it makes sense to test their germination rate. The Garden Shed article Good Seeds, Bad Seeds explains how to test seeds prior to planting.

Sharpening garden tools. Photo: R Morini

• Winter is a good time to clean and sharpen garden and cutting tools. Scrub them, rinse them in a 10% bleach solution and wipe dry. Sharpen cutting edges and oil blades and pivot points to protect their edges and maintain free movement. If you have a warm enough place to do it, wash and disinfect pots and planters the same way. It is great to reach spring with tools and pots ready to go.
• If you end up with a stack of plastic pots that you don’t need, recycle them. Some local nurseries will take them for their own or community reuse. Lowes has a chain-wide recycling program. Let’s keep plastic out of landfills!

Papa delivering worm to fledgling. Photo: R Morini

• A key to minimum chemical gardening is to create the most diverse eco-system you can in your yard and garden. Feeding the birds in winter is a good way to keep these helpful predators around for when they are needed. Get some tips on good bird feeder practice in The Garden Shed article Creating a Bird Friendly Garden.
• If you have a natural Christmas tree, please recycle it. Albemarle County has a recycling program with multiple drop off sites. They convert the trees to mulch that is offered free to residents.
• If you burn wood in your fireplace, and compost or add the ashes to the garden, remember that ashes are alkaline. They can be used as an amendment but will raise the soil pH if added in quantity. Not all plants can tolerate alkaline soils. Ornamentals including lilac, weigela, pinks and mock orange as well as vegetables including spinach, beets, corn and cabbage are exceptions. For more info, check The Garden Shed article Wood Ashes.
• If you really want to grow something, create an indoor herb garden. The Garden Shed article Be Inspired With Indoor Herb Gardening tells you how.
• Aphids, spider mites, whiteflies, and other pests are winter houseplant nemeses. To minimize pest damage, keep new plants separate from plants moved indoors, remove dead/damaged foliage and use soapy water and sticky-card fly traps around plants to help too. Detailed advice is found on the U of Minnesota Extension publication Managing Insects on Indoor Plants.

I hope that these activities will help you enjoy the winter break while increasing your gardening skills. Hope to see you next month at The Garden Shed.

SOURCES:

Featured Photo: Snow on the Cover Crop, by R Morini

“Plants Grown in Containers,” , NC State Extension,

Climate Resilient Vegetable Varieties | Piedmont Master Gardeners, by John Traunfeld, U of MD Extension specialist (printed in January 2023 Garden Shed).

How to Create a Garden Journal | Piedmont Master Gardeners, from Jan 2023 Garden Shed, by Pat Chadwick.

Using Seed Packet Information to Help your Garden Grow | Piedmont Master Gardeners, from January 2018 by R Morini.

Rain Gardens

• January 9, 2024
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For gardeners like me, rainfall is a blessing. Precipitation brings the promise of healthy plants and the ensuing joy of watching buds and blossoms burst forth. On the flip side, too much rain can be harmful or even destructive. A rain garden is an effective, natural method of filtering and controlling waterflow that also adds beauty to the landscape. What follows is an introduction to rain gardens to spark your interest in creating one on your own property.

What is a rain garden?

A rain garden is a shallow depression in the land, usually on a slope, that contains native perennials, flowering plants, grasses, and shrubs. By design, it is a temporary holding spot for rainwater runoff that comes from rooftops, driveways, sidewalks, lawns, and nearby hardscape areas. Basically, a rain garden collects rainwater, absorbs it, then slowly releases that water into the ground below. In so doing, a rain garden replenishes ground water and prevents the sudden gushing of runoff filled with potentially hazardous materials into various bodies of water.

Why create a rain garden?

The main function of a rain garden is conservation of water. A high volume of rain or sustained rainfall over a relatively short period of time produces unwanted stormwater runoff, especially from impervious surfaces such as concrete or asphalt. This stormwater carries just about everything along its way, from animal waste to fertilizer, pesticides, garbage, motor oil, gasoline, chemicals, and bacteria. Laden with these non-point source pollutants, untreated runoff flows into nearby streams, ponds, lakes, rivers, bays, and eventually into the ocean. According to data from the U.S. EPA, rainwater runoff is responsible for 70% of all water pollution, so this is a significant problem. A rain garden removes many of the undesirable contaminants and sediment through percolation, plus it enables 30% more water to soak gradually into the ground around the collection site. In other words, a rain garden improves water quality, supports flood control, and absorbs essential groundwater.

Beyond the functional benefits for water quality and physical terrain, a rain garden contributes to landscape aesthetics and provides sustenance for valuable pollinators such as birds, butterflies, and other insects. A rain garden should include native plants well-adapted to local climatic conditions that can handle high levels of moisture and thrive without fertilizer. These native plants are important sources of nourishment for local pollinators, who in turn help to ensure reproduction of those species. Once these plants are established (after the first year), they generally require very little maintenance.

How do you establish a rain garden?

As you approach the planning phase, keep in mind that a rain garden can be designed to fit your site and accommodate your preferences. Basically, the area should be approximately 20% of the surface area of your roof or the hardscape area near your house that will drain into the rain garden. If that’s not feasible for your setting, a smaller rain garden can still have a positive impact. A rain garden should be at least 10 feet away from your house and placed perpendicular to the natural slope for maximum stormwater capture. A 12% grade works well. Ideally, a rain garden is positioned to catch waterflow from a couple downspouts, and it should not be near a well, drain field, or septic system. Avoid the dripline of trees, since those roots may not be able to manage extended periods of soggy soil.

When determining the desired size and shape of a rain garden, aim for the length to be twice as long of the width. Curved designs, such as an oval or kidney shape, fit nicely into natural surroundings. The recommended depth of a rain garden varies, depending on soil type and texture. For clay soil, common in the Virginia Piedmont, the top 8-10 inches of soil should be removed and replaced with sand, due to slow infiltration. For sandy soil, remove 7-8 inches of existing soil and replace it with a mixture of sand and topsoil. For silty soil, dig up 5-6 inches of existing soil and amend that with sand and topsoil mixture. The rain garden should be a shallow depression just slightly lower than the surrounding earth.

IMPORTANT: Be sure you contact Ms. Utility in advance of excavation, so digging won’t interfere with buried electrical, gas, water, sewer, or telecommunications lines. Ms. Utility will mark those lines, so you know exactly where they are. TIP: Take photos for easy reference in the future.

Following excavation, make sure the bottom of the rain garden is level and scarified (scraped to make a rough surface, rather than smooth), and plan for soil amendments. Enhancing soil texture will improve the capacity of a rain garden to hold water, and enriching soil quality will help plants thrive. Depending on existing soil type (as noted above), a mixture of coarse sand and loamy compost should be added into the planting area. Optimally, a rain garden infiltrates water at about ½ inch per hour. You may want to conduct an infiltration test to determine whether the chosen site with amended soil will function well. By the way, a rain garden should allow water to seep into the ground within 36 hours, so that mosquitos do not have a chance to get established there.

Selecting Plants for a Rain Garden

The next step is the most enjoyable: choosing plants for your rain garden. Fortunately, many excellent online resources can help you make appropriate selections based on your chosen site conditions: size, full/partial sun or shade, soil type, grade of the slope, and possible need for deer-resistant plants. I highly recommend these free resources:

• Montgomery County, MD RainScapes planning document offers user-friendly planting design templates and detailed descriptions of recommended plants.
• Planning your garden from Rutgers University and the New Jersey Native Plant Society and Water Resources Program is also a fantastic guide.One of my favorite sources for choosing rain garden plants is from the University of Wisconsin Extension Program. This how-to manual provides plant lists by Latin and common name, bloom time and color, plus height and spacing requirements, with charts organized by soil type and sun/shade conditions. A terrific resource to make your dreams of a beautiful rain garden come true!

Maintenance of a Rain Garden

Good news! Once you have installed your rain garden, taking care of it is surprisingly easy. With native plants, only occasional watering is needed during dry periods, and you can avoid fertilizer and pesticides. Weeding is the main activity in the first year, but after plants are well-established, weeds are less likely to be problematic. You will also want to remove debris, such as leaves, from the rain garden to facilitate drainage and prevent that area from retaining standing water.

Does it work? My Experiment

As testimony to the effectiveness of a rain garden, I share my own story. This past year we built a new solar home on an elevated ridge in Earlysville. The house sits on a natural slope, so we were aware of potential issues with stormwater runoff. A rain garden seemed like a good solution. I designed one to: 1) capture rainwater from gutters and downspouts, 2) carry that rainwater in underground pipes, and 3) release that runoff into a kidney-shaped rain garden. This area is strategically located about 25 feet away from the house at a lower elevation. After observing waterflow on rainy days during the construction process, I figured out the natural pathway for that stormwater runoff.

We hired an excavator to dig a shallow hole at the identified location where the water-laden pipe from downspouts would empty on rainy days. We placed a layer of stones at the bottom because of clay soil here and topped it off with sand and then loamy topsoil. For aesthetic reasons, we added large boulders (from another part of our property) all around the rain garden. I researched, selected, and planted native species recommended for rain gardens, with shrubs, young plants, and seeds in the mix. I crossed my fingers that our set-up would work. Sure enough, just three weeks after our move-in, a torrential downpour arrived. Grass was not yet established, so I watched with trepidation as rivers of water went rushing downhill. Aha! The rain garden filled with water, serving as a temporary holding pond. Slowly, over the next few hours, that water seeped into the ground below. Without the rain garden, water bursting from downspouts would have gushed down into the pond and streams below our house, carrying good topsoil and whatever else the stormwater picked up enroute. So far, so good.

As you may recall, our region experienced a drought this past spring and summer. I was concerned about those new plantings and watered the rain garden every three weeks. I weeded the area a couple times, so that undesirable plants would not steal precious water. To my astonishment, the native plants survived and thrived. By September we enjoyed views of colorful flowers, tall grasses, and small shrubs with berries, which numerous pollinators visited on a regular basis. In November, I trimmed the longer stalks, leaving stems at a height of two feet for insects to use as homes during the winter months. As December began, the rain garden continued to be a source of beauty in our side yard, with friendly birds using the boulders and plants as landing spots while searching for food nearby. I would say my experiment was a success!

Conclusion

With this introduction to rain gardens, I hope you consider establishing one of your own. The resources below will give you a wonderful head start. Special thanks to Dorothy Tompkins for her expert input on this topic. A visit to Dorothy’s property during my PMG training was the initial inspiration that led me to create one!

 

 

Resources for Rain Gardens

Soak Up the Rain: Rain Gardens | US EPA

All About Rain Gardens – What They Are & How to Build One (groundwater.org)

RGPlantingDesigns2020.pdf (montgomerycountymd.gov)

Rain Garden Basics | Rain Gardens | Washington State University (wsu.edu)

How To Build a Rain Garden | Rain Gardens | Washington State University (wsu.edu)

Rain Gardens – A how-to manual for homeowners (dc.gov)

An Introduction to Rain Gardens (psu.edu)

https://www.epa.gov/watersense/what-plant

Water Resources Program at Rutgers NJAES

Rain Garden Manual of New Jersey by Rutgers Cooperative Extension Water Resources Program – Issuu

Basic Information about Nonpoint Source (NPS) Pollution | US EPA

Simplified hydrologic cycle (weather.gov)

https://extension.oregonstate.edu/sites/default/files/documents/12281/infiltration-testing-fact-sheet.pdf

 

The Ornamental Garden in January

• January 9, 2024
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• 0 Comments

The coldest temperatures of the year in the Charlottesville/Albemarle County area of Virginia have generally occurred in January.  Historically, this is also the driest month of the year.  Pay attention this month to weather-related issues in the ornamental garden such as frost heaving or broken tree limbs.  As you stroll through your property this month, take stock of the landscape without the distraction of foliage. Use this time to evaluate what changes, if any, you want to make.  If you have landscaping projects in mind for this year, now is a good time to start planning for them.

Inspect recently-planted perennials and other landscape plants for signs of frost heaving, which is caused by alternate freezing and thawing cycles.  Reposition any plants that have been pushed up out of the ground and make sure the roots are well covered with soil. Gently firm the soil around the roots and apply a layer of mulch to help protect them from freezing weather and drying winds.

Monitor trees, shrubs, and perennials that were planted this past fall to make sure they don’t dry out from lack of moisture.  In the absence of adequate rain or snow, provide newly-planted trees with about one gallon of water per inch of trunk caliper (trunk diameter at 12” above the ground) per week during the dormant months (November through March). Spread the weekly watering over a 2- to 3-day period, if possible.  Water when the temperature is above 40°F and there is no snow or ice on the ground near the trees.  Water early in the day so that the plants have time to absorb it before temperatures drop at night.  As a rough guideline, use a hose to water newly planted shrubs approximately 10 seconds per gallon plant size.  In other words, if the plant came in a 3-gallon container, water the root ball for about 30 seconds.

Gently brush accumulated heavy snow off evergreen shrub and tree branches to minimize breakage. Shaking the branches is not recommended.  If using a broom to push the snow off, use an upward rather than a downward motion.  For plants coated in ice, allow the ice to melt on its own. Otherwise, attempts to force ice off the branches may damage the plant.

Prune tree and shrub branches that have been obviously broken down by snow or ice.   For more information on this and other winter-related hazards, see Virginia Cooperative Extension Publication 426-500, Managing Winter Injury to Trees and Shrubs.

Inspect tree trunks and shrubs periodically for animal damage.   Winter damage to woody plants from deer browsing and antler rubbing is common throughout the area.  Small animals such as rabbits, mice, and voles can be just as destructive.  Through their chewing actions, they can cause a great deal of damage to the bark and trunks of trees and shrubs, particularly if other food sources are scarce in winter.  For details on preemptive actions that can be taken to protect woody plants from these animals, see this Iowa State University Extension publication: How to Protect Trees and Shrubs from Animal Damage Over Winter.

Inspect stored tender bulbs and tubers such as dahlias, elephant ears, and canna lilies to make sure they are firm and free of mold.  If the bulbs are shriveled, lightly moisten them. Make sure the temperature in the storage area is above freezing.

Clean dust from houseplant leaves periodically.  A layer of dust can block sunlight from foliage, which reduces the plant’s ability to photosynthesize.  It can also weaken a plant, making it more susceptible to diseases and insect infestations.  For detailed advice on how to remove dust from houseplants, see the Ohio State University Extension publication Why You Should Clean the Leaves of Houseplants.

Monitor houseplants for insect pests.  Dry indoor air can create the perfect environment for pests such as mealy bugs, spider mites, scale, white fly, and aphids.  For help with insect identification and recommended treatments, check out the Clemson Cooperative Extension’s Fact Sheet on Common Houseplant Insects and Related Pests.

Use de-icing products carefully on walkways, steps, or other icy surfaces to avoid damaging nearby plants. Avoid using ice-melting products containing nitrogen and phosphorus. Instead, try alternative de-icing methods that are safer for plants, such as sand, sawdust, or non-toxic de-icers.

Avoid excessive foot traffic on lawns over the winter months to prevent damaging the sod and compacting the soil. Also, avoid parking vehicles on the lawn.  The weight of the vehicle can kill or damage the grass beneath the tires.

Clean and inspect all garden tools to make sure they are in good working order. Sharpen any that need it.  This Oregon State Extension publication on Care and Maintenance of Garden Tools is one of many available on-line resources that describe good garden tool care.  For detailed guidance applicable to a variety of garden tools, check out Maintaining Lawn and Garden Tools and Maintaining Your Garden Tools.  Don’t forget to inspect and maintain wheelbarrows, lawn mowers, and any other gardening equipment you own.

Clean and sterilize flowerpots that are being stored for future use.  First, use a stiff wire brush to remove all dirt and debris.  Then, soak the pots for at least 10 minutes in a solution of one part bleach to nine parts water. It’s important to rinse the pots thoroughly after soaking to remove any residual bleach before reuse. Bleach is designed to kill biological life. Plants can be damaged by bleach, even weak bleach solutions.

Clean and sterilize soiled seed flats or seedling trays using one part bleach to nine parts water in anticipation of reusing them to start new seedlings; be sure to rinse thoroughly.

Use this dormant season to develop a list of tasks for the coming season’s garden.  Focus on plants to be divided, transplanted, added, or eliminated once the weather breaks this spring.

Don’t forget the birds!  Provide extra food and water from November to April to help the birds when natural food sources, such as seeds and berries, are less plentiful. Consider incorporating more shrubs and trees in the landscape that provide berries in winter. And don’t forget the Great Backyard Bird Count, which is a free, fun, and easy event that engages bird watchers of all ages in counting birds over a four-day period and reporting their sightings online.  For details see birdcount.org.

It may be January and plants with blossoms are certainly scarce at this time of year, but the ornamental garden can still be interesting!  So, pull on your boots, warm jacket, and mittens, and go look for plants with colorful berries, trees and shrubs with interesting bark or branching, lichens, mosses, dried grasses, dried seed pods, conifers, hardy ferns, and other evergreen plants.   If you really do yearn to see something in bloom, check this link to the Lewis Ginter Botanical Garden for a listing of “January Blooms.”

Featured Photo:  Pat Chadwick

Upcoming Events

• January 9, 2024
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How to Prune Landscape Trees

—Tuesday, January 16 @ 7:00 to 9:00 p.m.  via Zoom

⇒ Register here. This class is FREE (donations appreciated)

Join tree steward Tim Maywalt for this informative class to learn the best practices for pruning landscape trees to improve their health and appearance while reducing the risk of branch failure.  Topics covered include:  basic tree pruning concepts; where, when and what to prune; how to minimize decay resulting from pruning cuts; types of pruning cuts; and tools, tool maintenance and safety. The class will mainly focus on young landscape trees.  It will not cover pruning fruit trees for production, pruning shrubs, nor topiary.

 

Coming up in February . . .

 

 

Soil Compaction

• January 9, 2024
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• 0 Comments

Growing roots exert a pressure of up to 25 atmospheres – equal to the pressure you’d feel 800 feet under water. Yet compacted soil will stop roots dead in their tracks. This article will discuss how soil gets compacted, and how to mitigate and prevent compaction in lawns, vegetable gardens, and landscape areas.

A brief primer on soil structure

The fundamental particles of soil are tiny bits of various minerals – essentially, weathered rock. Organic matter holds these soil particles together, forming aggregates. Tiny aggregates themselves associate into larger aggregates, again held together by organic matter (see picture). Fungal hyphae and fine root hairs also help to generate aggregates.

The amount of aggregation determines the structure of the soil. If a soil has many large aggregates, there will be many large pores between the aggregates because the aggregates can’t fit tightly together. In a healthy, well-structured soil, pores make up half the volume of the soil. Soils with poor aggregation have less pore volume because their small aggregates pack tightly together (see picture).

Pores are essential for plant growth:

(1) Pores are filled with air and water. Pores usually contain about equal amounts of each, depending on how wet the soil is. Roots absorb nutrients dissolved in the water, for example potassium, calcium, and iron. Roots also absorb the air in the pores, providing the oxygen that roots need to grow.

(2) Pores provides pathways for root growth.

Compaction, on the other hand, destroys soil pores by squeezing aggregates together – which, as discussed above, is easier when aggregates are small. This starves plants of nutrients and creates a physical barrier to root growth. Two practices can prevent, and to some extent reverse, compaction:

(1) Promote aggregation by giving soil plenty of organic matter. 5% organic matter is a typical level for a healthy soil. A soil test can measure organic matter. Soil test kits can be picked up at the VCE office at the Albemarle County office building at 460 Stagecoach Road in Charlottesville.

(2) Avoid physically compressing soil by minimizing foot and machine traffic. If traffic is unavoidable, wait until the soil is dry before walking or driving on it.

Below are recommendations for mitigating and preventing soil compaction in a few locations around the home.

Vegetable gardens

Preserve organic matter by eliminating or minimizing tillage. No-till is counterintuitive (and controversial). Tillage certainly softens the soil’s top layer in the short term. In the long run, though, tillage depletes the soil’s organic matter by over-aerating the top few inches of soil. Soil microbes respond to the increase in oxygen and consume the soil’s organic matter. This, in turn, causes soil aggregates to fall apart. (Some experts do suggest one-time tilling of compost into new beds to speed up soil improvement.)

Instead of tilling, add organic matter by spreading compost or mulch over the surface of the soil. The organic matter will work its way into the soil over time. Accelerate the infiltration of organic matter by loosening the soil with a spading fork, broadfork, or garden rake. This opens up small gaps in the top few inches of soil, but without excessive aeration and aggregate breakdown .

Cover crops are another effective way to add organic matter and loosen the soil. There isn’t space here for an-depth discussion of cover crops, but Piedmont Master Gardener Cleve Campbell has written a great introduction to cover cropping. Cover crops’ roots add organic matter to the soil. Clovers, and legumes like hairy vetch, boost soil nitrogen as well. Cover crops’ roots also break apart compacted soil. Forage radishes are particularly good at punching holes in heavy soils.

Terminating cover crops is another complex topic, covered in detail here. It’s important to terminate cover crops before they go to seed and become weeds! Don’t till cover crop residue back into the soil, for the reasons mentioned above. Rather, cut the cover crop at the soil’s surface using a stirrup hoe or hand sickle – or even a lawnmower. Compost the cover crop residue or simply leave it on the soil surface, a practice termed green manure. The residue will decay and release organic matter into the soil.

Finally, minimize foot or machinery traffic on the cultivated parts of the garden. Paths between the garden beds are a good way to keep traffic off the cultivated beds. If you must stand or kneel on the beds, support your weight on a board to spread the pressure out.

Lawns

Aeration is the best way to alleviate compaction in lawns. Usually this is done with a rented machine. Find a device with hollow tines or spoons that bring soil cores up to the surface. Spikes or blades that cut into the soil aren’t as effective: they let some air into the soil, but also create compaction around the holes they cut. Spiked shoes also are not a good solution, for the same reason.

After aerating, it’s not necessary to remove the cores. If you don’t mind the appearance, simply wait for them to fall apart. A faster method is to wait a few days, until the cores have dried a bit, then rake them into tiny pieces and compost or leave in place. If desired, follow up aeration with overseeding, fertilizing, and liming. (Don’t apply lime without first doing a soil test to measure soil pH.)

The best time to aerate is when the grass is growing at its maximum rate. In other words, aerate in spring or fall for cool-season grasses and summer for warm-season grasses. Also, don’t aerate when the ground is very dry; this will decrease the effectiveness of the aerator and may even damage the tines. Also avoid aeration when the ground is very wet; this can make compaction even worse.

How often should you aerate? A home lawn shouldn’t need aeration more than once a year. If you notice water puddling, this is an obvious sign that compaction is a problem. Similarly, heavy thatch – the layer of mixed living and dead material between the grass blades and the soil – is a sign of compacted soil. If the thatch is more than an inch thick, it’s time to aerate.

Prevent compaction by minimizing foot and machine traffic. Of course, foot traffic is a main reason for having a lawn! Paradoxically, one solution is to concentrate traffic in a small area, for example by making pathways of mulch or stepping stones in high-traffic areas. Similarly, sometimes machine traffic is unavoidable. Don’t drive machinery across lawns when the soil is very wet. Drive machinery on boards or sheets of wood to spread out the weight.

Landscapes

Compaction in landscaping is tricky because these areas don’t lend themselves to invasive methods. Moreover, trees and shrubs are particularly sensitive to compaction because their roots extend quite far from their trunks.

Alleviate compaction by adding organic matter to the surface, in the form of mulch. The mulch will break down and organic matter will, slowly but surely, fall into the soil below. Wood chips, shredded bark, and mulched leaves are good choices, inexpensive (or free) and easy to obtain. Allow leaves to decompose in place under trees. If leaving leaves in place is for one reason or another unacceptable, rake the leaves onto some grass, shred them with a lawnmower, and return them to the area under the trees.

Under trees, mulch should extend to the outer extent of the branches (see picture). This perimeter is called the drip-line of the tree. The mulch should be only 2-4” deep. Any deeper and it will impede decomposition and release of organic matter into the soil. Don’t mound any mulch against the base of the tree trunk – the notorious “mulch volcano” (see picture). If mulch covers the bark, moisture can cause the bark to rot, and animals may gnaw on the covered bark. The root flare – the widening of the trunk where it begins to divide into roots – should be visible.

A professional arborist may use an air spade to loosen heavily compacted soil around a tree. An air spade uses supersonic jets of air that remove soil – even when heavily compacted – but leave roots largely undamaged. After removing a few inches of compacted soil, higher-quality soil, with plenty of organic matter, is added in its place. Needless to say, this is an extreme, and expensive, solution.

Given the difficulty of remedying compacted soil in landscape areas, prevention is critical. Mulch works very well for this because it discourages foot traffic. Direct foot traffic away from trees and shrubs using pathways of mulch or stones. Don’t drive or park heavy machinery near landscaped areas.

Closing thoughts

Soil compaction is a serious problem anywhere humans have disturbed the soil, whether in a yard, a cityscape, or a farm. Prevention is by far the best way to combat compaction because compaction is hard to reverse, particularly in a short time. Adding organic matter to the soil, in one way or another, is the primary way to alleviate compaction. This, as discussed in the “primer” section above, promotes aggregation of soil particles and a robust network of pores that allow root growth and infiltration of air and water into the soil. The other key practices are an observant eye, for signs and symptoms of compaction, and, of course, patience.

References and further reading

Elements of the Nature and Properties of Soils, 4th Edition. Ray R. Weill and Nyle C. Bandy
Air trench digging or loosening soil. University of Florida
Assessing and addressing soil compaction in your yard. New Jersey Agricultural Experiment Station
The Biology of Soil Compaction. Ohio State University Extension
Cover crops. Cleve Campbell, Piedmont Master Gardener
Forage radishes, a hard-working cover crop. Cleve Campbell, Piedmont Master Gardener
How to control thatch in your lawn. University of Minnesota Extension
Management of compaction – coring. University of Massachusetts Extension Turf Program
Managing soil compaction. Oregon State Extension
Mulching landscape trees. Penn State Extension
Physical Root-Soil Interactions Physical Biology 2017 (PDF). Evelyne Kolb et al.
Problems caused by compacted soil. University of Maryland Extension
Restore compacted soils. University of Colorado and U.S. Botanic Garden
Scraping: scuffle hoes. University of California Agriculture and Natural Resources
Strategies to avoid and manage soil compaction. University of California Agriculture and Natural Resources
Understanding soil compaction. New Jersey Agricultural Experiment Station
Virginia Tech Soil Testing Lab
Walkways in the landscape. University of Florida
What to do about compacted soils. Michigan State University Extension
Featured image: Volker Prasuhn, Wikimedia Commons (public domain image).