Climate Change

Free the Flare: Maintain Visible Root Flare for Tree Health

Maryland Grows4 Comments

Tree planting efforts are picking up as Maryland’s 5 Million Trees Initiative moves forward in 2024. Getting these trees – any landscape trees – off to a good start at planting time and through their first few years of establishment is important for their long-term growth and benefits to the environment.

At Ask Extension, we often receive photos of newly planted trees and older specimens with signs and symptoms of trouble. One of the things we do in our diagnostic process is look to see if there is a “root cause.” Is a girdling root present at the base of the tree trunk? Is the tree planted too deeply? Can we see a root flare? Today I want to bring these questions to the surface and explain why an exposed root flare can help prevent the formation of girding roots and why it matters for tree health and pest management.

a beech tree with a nice sloping visible root flare above the soil line
A beech tree with normal, healthy root flare. Photo: Miri Talabac, University of Maryland Extension (UME)

What is a root flare?

The root flare is the area at the base of a tree trunk where the topmost roots emerge outward. This area is sometimes referred to as the trunk flare or root crown. In many species of trees, the trunk widens and curves outward (“flares”) like the base of a wine glass. This is illustrated nicely in this brief video by the University of Maryland Arboretum and Botanical Garden’s Outreach Coordinator, Meg Smolinkski.

What is the root flare of a tree?

When thinking about the trunk and root system of a tree, it is important to keep in mind: Roots need to be in the soil to get a steady supply of moisture and nutrients. The trunk (stem) portion should be out of the ground where exposure and good airflow help to keep the bark dry. 

In our landscapes, we have many trees that are planted too deeply and the root flare is not visible at all. The trunks go straight into the ground like telephone poles. This can result in lower bark rotting, reduced oxygen supply to the roots, disease and pest problems, and girdling roots.

We have an epidemic of planting trees too deeply

At the University of Maryland Extension Advanced IPM Conference for the commercial horticulture industry last month, Jacob Hendee, an arborist for the Smithsonian Institution Gardens, talked about how common it is nowadays to see trees planted too deeply. Burying the root flare has reached “epidemic” proportions in our landscapes, he noted – and it is killing trees.

The main problem he addressed in his talk was that buried root flares can set the stage for stem girdling roots to develop unnoticed. Stem girdling roots (SGRs) grow around the tree’s base, rather than pointing outward away from the trunk as normal roots should. As girdling roots grow and enlarge, they compress the water- and nutrient-conducting tissues in the tree. This interrupts normal plant functions and can lead to symptoms such as leaf yellowing (chlorosis), smaller-than-normal leaves, leaf scorch (browning), branch tip dieback, and bark cracking. SGRs can and do result in overall tree decline and eventual failure.

girdling roots are present at the base of a tree that has too much mulch
An example of girdling roots. Photo: M. Talabac, UME

An illustration showing the growth of sapwood in a tree - In year 5 it is all sapwood, in year 10 the sapwood outlines the heartwood and in year 15 there is a larger ring of sapwood on the outside circumference
Looking at a cross-section of a tree trunk, the light-colored portion is the water-conducting sapwood (xylem). Source: Jacob Hendee, Smithsonian Gardens

An illustration showing how a stem girdling root grows around a trunk and constricts - limits the growth of the water conducting xylem ring
When a stem girdling root forms around the trunk of a tree (represented in orange in the diagrams), it compresses and kills the water-conductive sapwood, which can result eventually in a dead tree. Source: Jacob Hendee, Smithsonian Gardens

Trees under moisture stress due to stem girdling roots become more susceptible to pests and diseases. Scale insects are significant pests of some landscape trees, as are some types of beetles and other insects. If a tree develops a pest issue, the pest may be secondary to the problem that made the tree vulnerable to the pest in the first place – stress. 

Hendee emphasized that maintaining a visible root flare and preventing SGRs are practices of Integrated Pest Management (IPM). IPM involves using physical, cultural (plant care), and biological methods to manage pests and diseases, leaving chemical pesticides as a last resort. In the example of tree care, correct planting and monitoring to prevent stem girdling roots are key steps to preventing tree stress. Instead of thinking about killing secondary pests that show up on trees, think about how to prevent stressful growing conditions from the beginning and during the life of a tree. Trees with minimal stress are more resilient to insect pests and less likely to be overwhelmed by them or need intervention to recover.

How do stem girdling roots get started?

Hendee noted that plant care practices, both before planting (at the nursery), during planting, and afterward (over-mulching) contribute to this problem. 

1. Many trees are grown too deeply in the nursery. Girdling roots can start to form inside nursery pots when the roots hit the container and start circling. This issue can worsen when young trees are moved into larger containers as they grow (such as saplings being transplanted into a bigger pot as they mature) and their roots are not loosened or pruned to correct deformities. Larger trees are sometimes planted too deeply in the nursery field and come to the customer in “ball and burlap” form with the root flare already covered in soil.

2. Many trees are planted too deeply at the time of installation. If the planting hole is dug too deeply, the root flare gets buried when the soil is filled back in, and often then further covered with mulch. In that situation, stem girdling roots can develop and worsen undetected.

3. Tree flares are often buried deeply in mulch. Too often we see huge piles of mulch – sometimes one foot high or more “mulch volcanoes” – around trees. This will keep the bark moist and can encourage new roots to sprout from the trunk above the main supporting roots (the flare). Those adventitious roots will grow upward for oxygen and may begin to girdle the flare and trunk. They will also be more vulnerable to moisture stress since the mulch does not retain water in the same way soil does. There is absolutely no horticultural basis for putting a big mound of mulch around a tree like this!

Mulch piled over 1 foot high around a young tree near a parking lot - there is no visible root flare - this is a mulch volcano
An example of incorrect mulching. Photo: Dr. David L. Clement, UME
mulch was incorrectly placed on top of a girdling root around the base of a tree
Here fresh mulch was incorrectly placed on top of a girdling root and up against a tree trunk. Photo: C. Carignan, UME

What can you do? “Free the Flare”

1. Check the roots at planting time.
If you purchase a container-grown tree, ensure it is free of circling roots inside of the pot. If you do find roots that are circling the root ball, cut through those roots with a pruner or other sharp tool. Set the roots in the planting hole so that they are pointing in an outward direction.

Prevent girdling roots when planting a container-grown tree


2. Keep the top of the root flare visible.
Root flares should be above the soil line. Plant so the root flare is 2 to 4 inches above grade. When purchasing a container-grown or burlapped tree, you may need to wash away some of the soil to see where the root flare begins. If a landscaper is installing a tree for you, make sure they set the tree at the correct depth.

soil from a container-grown tree was washed away to reveal that the top of the root flare had been sunken too deeply in the pot
A hose was used to wash away the soil from a container-grown tree, revealing the top of the root flare. The difference in the lower bark color (on the trunk) indicates that the plant was several inches too deep in its container. Photo: M. Talabac

When a root flare is visibly present, it can help deflect any stem girdling roots that begin to grow, forcing them away from the trunk. It also makes it easier to see where girdling roots begin to form. Monitor the root flare area of your tree(s) regularly and cut through any circling roots that begin to grow. It is easier to cut wayward roots when they are small. The process of locating and remediating stem girdling roots on older trees can be very expensive.

Also note that some species of trees are more prone to developing girdling roots (e.g., maples), and sometimes girdling roots develop below the soil surface where they are not easily detectable except by above-ground clues. If you see symptoms of water stress in the canopy of an otherwise sufficiently-irrigated tree (e.g. leaf scorch, smaller-than-normal leaves), consult with a certified arborist for a tree assessment.

3. Don’t overdo it with the mulch!
Keep a mulch-free buffer zone around the root flare. Hendee suggested leaving a 3 to 12-inch area bare around the base of the tree. Think of it as a donut hole: mulch should be laid down in the shape of a wide, shallow donut rather than a big heaping mound. The total depth of the mulch should be only about 2 to 4 inches.

how to mulch correctly - free root flare - mulch free buffer around the base of the trunk - 2-4 inches of mulch depth - broad mulch width
Mulch applied correctly. 1 Free root flare, 2. Mulch-free buffer around the root flare, 3. 2 to 4 inches mulch depth, 4. Broad mulch width. Infographic by Smithsonian Gardens

For further exploration of these topics and correct tree-planting procedures, I recommend the following resources:

Show Me Your Root Flare (PDF) | Clemson University

Girdling Roots | University of Maryland Extension

Planting and Care of Trees | University of Maryland Extension

Problems With Over-Mulching Trees and Shrubs | Rutgers

By Christa Carignan, Certified Professional Horticulturist & Coordinator, University of Maryland Extension Home and Garden Information Center. Read more posts by Christa.

Illustrations used with permission from Jacob Hendee, Smithsonian Gardens

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Composting and Climate Change

Maryland Grows3 Comments

Composting is probably seen by most people as good for gardens and the environment. After all, compost helps make our soils and plants healthier and keeps green waste from our yards and kitchens out of landfills.

But is composting good in the context of our climate crisis? Doesn’t the composting process generate lots of carbon dioxide (CO2), the principal greenhouse gas (GHG) that traps heat in Earth’s atmosphere? Can composting also mitigate climate change and make our yards and landscapes more climate-resilient? The answer to both questions is YES. This article will show that composting, at the home, community, and municipal/commercial level, is an important global warming mitigation and adaptation tool. As we’ll see, the ways that humans manage this natural process and use the compost can affect the climate benefits.

Composting basics

We don’t make compost! Huge populations of microorganisms do most of the work and we humans manage the process for our benefit. It’s nature’s way of recycling anything that lives and dies, like plants, animals, and microbes.

The decomposition process produces lots of carbon dioxide (CO2), part of the world’s carbon cycling system shown in this graphic:

illustration of the carbon cycle - plants use carbon dioxide from the air and water from the soil to build carbohydrates
Plants exude carbohydrates through their roots to feed soil organisms. Those organisms release carbon dioxide through respiration. Illustration by Jocelyn Lavallee, Ph.D., Soil Scientist

This CO2 release is considered biogenic (happens through natural biological systems), not anthropogenic (people-made), and is not included in the calculations of greenhouse gas (GHG) emissions that drive global warming and climate change.

The three primary GHGs are:

  • Carbon dioxide (CO2) — 300-1,000 year atmospheric lifetime; 86% of total GHG emissions
  • Methane (CH4) — 84X the global warming potential of CO2; 12 year atmospheric lifetime; 7% of total GHG emissions
  • Nitrous oxide (NO2) — 265X the global warming potential of CO2; 100 year atmospheric lifetime; 6% of total GHG emissions

There are many factors that determine the potential for composting to generate methane and nitrous oxide, like the mix of materials being composted, temperature, moisture, pile size and configuration, and aeration. Compost piles and windrows that are waterlogged and low in oxygen (anaerobic) are more likely to generate these GHGs. Composting is “climate-friendly” when it’s done in the presence of air (aerobic). Home and community composters turn piles by hand to keep them aerated and large-scale composting facilities use mechanical turners and force air into windrows with blowers. Well-managed composting at any scale releases very little methane or nitrous oxide into the atmosphere. 

Direct climate benefits of composting

  • Dumping food wastes and grass clippings in landfills generates large amounts of methane because the decomposition process is anaerobic. Landfills release about 17% of total U.S. anthropogenic methane emissions and food waste makes up 24% of landfill space. Burning organic wastes releases GHGs and toxins. Composting these organic wastes using best practices greatly reduces emissions.
  • Carbon sequestration: Compost continues to degrade after soil incorporation. Some of the carbon cycles through soil microorganisms and some is held tightly to clay particles, protected against decomposition, and becomes part of the long-term reserve of stored carbon.

Indirect climate benefits of composting

The mid-Atlantic climate is becoming wetter and warmer overall, punctuated by localized extreme weather events, like record-breaking rainfall and extreme drought and heat. Intense storms can cause soils and nutrients to wash away and warmer temperatures cause more rapid organic matter decomposition and turnover, especially if soils are tilled and uncovered.

Adding compost to soils makes them more resilient by:

  • Holding more water in the soil during periods of drought and extreme heat
  • Reducing erosion (washing away of soil during extreme rainfall) and nutrient run-off) due to improved soil structure (larger, more stable aggregates or crumbs)
  • Improving plant growth, by slow release of plant-available nutrients
  • Reducing the need for synthetic nitrogen fertilizers which require natural gas for their production
  • Reducing the need for potassium and phosphorous fertilizers (derived from mined mineral deposits that are dwindling worldwide)
  • Binding and degrading toxic metals and pollutants
  • Substituting compost for peat products can help reduce the release of CO2 from commercial peat extraction from wetlands 
illustration of how compost combats climate change - increases water holding capacity - sequesters carbon in soil
Poster by the Institute for Local Self-Reliance

Home composting

Managing and recycling as much yard waste as possible on-site is often the most climate-friendly approach because it reduces GHG emissions from transporting and processing or landfilling organic waste. You can do this by recycling grass clipping (“mow ‘em high and let ‘em lie”), mulch-mowing tree leaves and leaving them in place, or using them as mulch, composting yard and garden waste, and burying kitchen scraps. These practices help to recycle nutrients on-site and increase soil organic matter. Selecting or building a non-plastic composter can also help reduce GHG emissions.

Municipal/commercial composting

This is the next best option for organic wastes that cannot be managed on-site. Commercial and municipal composting operations do create GHG emissions from the trucks and equipment, powered by fossil fuels, that are used to collect, transport, and process organic waste and compost. The closer the source of organic waste to the facility the lower the emissions and the greater the benefits. On balance, composting on a large scale can also help mitigate climate change.

illustration showing that the carbon sequestration benefits of municipal composting outweigh the greenhouse gases generated by transportation, storage, and processing compost

To summarize: aerobic composting reduces GHG emissions compared to the landfilling and incineration of organic wastes. The resulting compost sequesters carbon when mixed into soils and improves soil health and resiliency. Composting at home and in your community is the most climate-friendly approach but commercial and municipal composting is another important tool that helps mitigate climate change.

References

By Jon Traunfeld, Extension Specialist, University of Maryland Extension, Home & Garden Information Center. Read more posts by Jon.

Vegetable Problems Update

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Wildfire smoke

Persistent wildfire smoke is new for Maryland gardeners. Experts seem to agree that smoke and ash do not pose a health risk for garden produce. Smoke diffuses sunlight but will probably not significantly reduce the total amount of light for photosynthesis. We have not heard/seen any reports of gardeners picking up smoky flavors in harvested greens or other vegetables or fruits.

  • Wash all produce prior to eating it raw or cooking with it
  • Wear an N-95 quality mask when working outside on days when wildfire smoke worsens air quality
  • Hose off plants if a noticeable soot layer develops from prolonged, intense smoke

Wildfire smoke has been shown to boost the levels of ozone and other air pollutants which can injure plants. Watermelon, squash, pumpkin, beans, and potato are especially vulnerable to high ozone levels (above 75 ppb).

Drought and damaging storms

Wildfire smoke interfered with weather patterns and likely contributed to cooler and drier weather across much of the state. 

Mid-May through June:

  • Lower average temperatures
  • 75% of state in moderate drought on July 3rd
  • Slow start for warm-season crops

July:

  • High heat and humidity
  • Spotty rainfall
  • Insect and disease issues increasing
Maryland drought status map
The Maryland Department of the Environment announced a Drought Watch on July 10, encouraging voluntary reduction in residential water use.
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Plant shopping soon? Avoid buying invasive plants

Maryland Grows4 Comments

It’s a sunny day in late February and that means I’m looking at seed catalogs and dreaming of new plants! Have you been plant shopping yet this year? Adding new plants and seeds to your garden creates new scents, textures, colors, and shapes and is the easiest way to increase biodiversity in your landscape!  

As you begin revitalizing your garden space this spring, I want to bring some attention to invasive plants, a category of plants that should strike fear and dread in your heart! Okay, maybe that’s a bit dramatic, but truly this is a topic that everyone needs to learn more about. 

Q. What is an invasive plant?

A. An invasive plant is a non-native, “alien” species that was introduced intentionally or by accident into the landscape and causes ecological and/or economic harm. These plants tend to be free from predators, parasites, and diseases that could help keep them in check. These plants reproduce rapidly with multiple methods (i.e. seeds, stolons, root cuttings, runners, etc.) and spread aggressively. They tend to be deer resistant or deer tolerant, a big reason why they are purchased and planted in landscapes. Below is a photo of purple loosestrife. Notice how it is creating a monoculture, a visual key that might mean the plant is “invasive.”

purple loosestrife flowers crowding a field
Invasive purple loosestrife (Lythrum salicaria).
Photo: Richard Gardner, Bugwood.org

Did you know that some invasives are still for sale at nurseries, greenhouses, and in mail-order catalogs?   

It’s true. Many of the plants on “watch lists” are still readily available to purchase. Japanese barberry is an invasive plant that is a very popular landscape plant still being widely planted today; however, research shows that black legged ticks have been found in areas with invasive barberry thickets because these non-native, invasive forest shrub thickets create ideal microclimates.   

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Centering vegetables

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In the days after Thanksgiving, I was casting around for something to write about in this blog post, when my husband surprised me at dinner with this masterpiece:

(From a Washington Post recipe; he used pine nuts instead of almonds because that’s what we had.) 

So I began to think about the idea of vegetables as centerpieces for the table. We are not vegetarians and this meal did include meat, but it was off to the side, not the focus of attention. Now, anyone who reads my posts here knows I love growing, cooking, and eating vegetables. When I go out to a restaurant, the kind where vegetables aren’t “sides” but a part of a constructed meal, I generally read the menu descriptions backwards and often choose the entree I’m ordering based on the vegetable accompaniment, deciding that I’m in the mood for parsnip puree or butternut squash risotto and that delicious-sounding salsa, and only afterwards acknowledging that the meat it comes with is just fine. (I’m also a sucker for unusual produce; I once ordered a meal at a restaurant in Oregon that was… probably fish? I don’t recall, but what sticks with me is asking the waiter what sea beans were, and when he was unsure, placing the order anyway and then pulling out my phone to search. They were great; can’t grow them here, alas, because they require a salty environment.)

But the point of those restaurant meals, and most of the ones we eat at home, is that the meat is in the middle. Even many vegetarian meals center a protein element that explicitly substitutes for meat, from plant-based burgers to Thanksgiving Tofurky. Many meals don’t, of course; pasta, pizza, and stir-fries are a few of many examples that combine elements from different food groups. But don’t we tend to describe them in terms of the protein, unless they’re a side dish themselves? How often do we talk about, yum, that dish I made with Chinese broccoli and those wonderful little peppers, oh and by the way I also put in chicken?

I think this is very much a cultural thing, and this is not the place to try tracing it through American history and sociology and noting the influences of and changes in various immigrant communities. I also don’t have the expertise to tell you exactly how much protein you need in your diet based on what food choices you make, and where you can find that protein. I do know, however, that it’s possible to eat healthily while thinking of meals in the way we’ve come to consider inside-out, that is with the vegetables first. This doesn’t have to involve spectacular centerpieces that take hours to cook; the pumpkin stuffed with onion, apple, fennel and cornbread, with maybe a little bacon for fun, can be relegated to the big holiday meal. But vegetables can at least be first in our meal planning part of the time. Maybe even all of the time.

Tamar Haspel, who writes for the Washington Post about larger perspectives having to do with diet, had a recent article about which plant foods are most and least impactful on our climate. (All plant foods are usually better climate choices than meat.) She concluded that fruit, nuts, and row crops such as grains and beans are better in an environmental sense than vegetables like lettuce, broccoli, and tomatoes, because the latter use more fertilizer and pesticides, go bad quicker and so contribute more to food waste, and provide fewer calories per acre. What this doesn’t account for, of course, is growing your own. Your home-grown veggies have zero crop transportation costs, and you will likely be using a lot less in the way of inputs. So I think you can eliminate climate guilt from the equation if you plant a garden. (Buying locally-grown produce would be the next best option.)

What are the best crops to grow if you’re trying to center vegetables on your table? Anything you like and will eat, basically, but if you’re going for the big centerpiece, think about squash or peppers that can be stuffed, beefsteak tomatoes (especially colorful heirloom types), or indeed cauliflower, though you’ll have to keep up with the fertilizer and water to achieve big, fully-formed heads, especially for a spring crop. Also think about ingredients you’d like to add to savory pies, galettes, or other pastries, or quiches and frittatas, or casseroles. Greens make a great base for many other dishes, or can star on their own mixed in with pasta or grains. And there’s always a big salad filled with lettuce, arugula, herbs, cucumbers, etc. – oh, and maybe some meat or fish too.

I’m still trying to shift my thinking from saying, when making meal plans, “We’ll have pork chops and…” “We’ll have macaroni and cheese and…” to a vegetable-centered focus. Here is a big lovely winter squash, I might think—what meat goes with that? Or maybe cheese and nuts? Can they go inside? Those Yellow Cabbage Collards I grew and put in the freezer: great with a little ham and a high-protein grain. I mean, sometimes we’ll just want a steak and potatoes with the greens on the side, but it’s worth doing the vegetable mind trick several days a week. And when there’s a little leftover steak, it might add something to a stir-fry of broccoli and beans.

If you’re looking for recipes, either search online for the vegetable you want to feature and “main dish,” or use a cookbook, vegetarian or not, that makes vegetables or vegetable families one of its primary organizing principles. And when you’re browsing the seed catalogs that are starting to arrive, consider what you might like to grow next year that will feature as the center of your table.

By Erica Smith, Montgomery County Master Gardener. Read more posts by Erica.

Food waste reduction: It’s everyone’s job!

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Our society wastes food at every point in the food chain from farms and gardens to home kitchens, restaurants, supermarkets, food service companies, and large institutions like universities that feed  thousands of people daily. Last December I was astonished to lean about the extent of food waste at the MD Food Recovery Summit organized by the Maryland Department of the Environment. 

Surplus food is the term used to describe unsold and unused food, like crops that don’t go to market because prices are too low, perishable items tossed into supermarket dumpsters, and groceries and restaurant meals bought and not eaten. 

In 2019:

  • 35% of all U.S. food went unsold or unused 
  • 23% of all surplus food is fruits and vegetables 
  • Only 15% of Maryland’s 900K+ tons of food waste was recycled 

Why it’s a problem:

  • Huge economic and environmental costs of producing surplus food
  • 1 in 6 U.S. residents are food insecure. Surplus food can feed hungry people
  • Surplus food is the #1 landfill material (24% of landfill space) 
  • Food waste in landfills generates methane, a potent greenhouse gas that can trap 28X as much heat/mass unit as CO2
  • The value of wasted food at the consumer level is $161 billion/year
Compost, recycle, and trash bins
Food scrap collection at Maryland Day event at UM/College Park campus. Photo credit: Jon Traunfeld
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Cover crops for climate-resilient soil: Try it, you might like it

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Cover crops are so important for improving soil and protecting the environment that it’s public policy in Maryland to use federal funding to subsidize farmers to plant them. Nearly ½ a million acres across the state are enrolled in Maryland’s Cover Crop Program. Cover crops protect Maryland’s farm fields from soil loss over the winter and scavenge the soil for the fertilizer nutrients that weren’t used by corn and soybean crops and might have moved into groundwater and surface water. 

Cover crops are typically planted from late August through October and include grasses like winter rye, winter wheat, barley, and oats and legumes like crimson clover and hairy vetch. Plants in the legume family, together with special soil bacteria, transform nitrogen from air into a plant-available form. Tillage radish (a type of daikon radish) and other plants are also grown as cover crops. 

Cover crops improve soil health and help make soils more resilient to the climate crisis. They

  • increase soil organic matter and carbon sequestration by feeding soil microbes with sugars and other root exudates 
  • improve soil structure and the strength of soil aggregates which lowers erosion risks
  • increase water holding capacity which allows crops to withstand drought better   

Cover crops use the sun’s energy (when food crops aren’t growing) to produce biomass- roots, shoots, and leaves. The cover crops are killed in the spring. Nutrients in the decomposing plants are eventually available for uptake by the roots of the vegetables and flowers we plant. This reduces the need for synthetic fertilizers, whose production requires fossil fuels.

What’s good for ag soils is also good for garden soils! 2022 is the Year of Soil Health for Grow It Eat It, the food gardening program of the UME Master Gardener program. This infographic by Jean Burchfield introduces the idea of planting cover crops, a key practice in building healthy soils: 

Infographic about cover crops

Photo of seed packets
UME Master Gardeners distributed 5,000 crimson clover seed packets for residents to plant in flower and vegetable beds this fall.
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