By Wendy Mills, Certified Master Gardener
Volunteers at the Glencarlyn Library Garden often comment on the quality of our soil, expressing pleasure with its good feel and workability. Here at the garden we understand that nutrient-rich soils are the foundation of any successful garden and that this doesn’t happen by accident. Soils in Northern Virginia tend to be clay-heavy and low in organic matter, so creating good soil —with a healthy mix of minerals, organic material, water and air—requires ongoing effort.
Below the surface, healthy soils are teeming with earthworms and insects, as well as trillions of microorganisms (bacteria and fungi) that feed on living or dead plants and animals, breaking it all down into rich humus. In a virtuous cycle that science still does not fully understand, specialized microbes known as mycorrhizae fungi form symbiotic relationships with host plants, colonizing their root systems and enabling the plants to absorb water and essential nutrients. In return, host plants, through photosynthesis, provide carbohydrates that the microbes need for energy.
Gardens with rich, dense and diverse plantings—not bare land—attract and provide food for these organisms. They, in turn, move through the soil, aerating, enriching and making it more porous and absorbent. Whatever your “crop”—perennials, annuals, vegetables or fruits—you can join the growing movement of “soil gardeners” who care for their soil in order to grow better, more successful gardens.
Here are some tips for improving your soil
Test your soil:
This is the only way to determine if phosphorus, potassium, calcium or magnesium must be added to the soil, or if a pH adjustment is needed. Without a soil test, any application of fertilizer could be detrimental to the landscape. Soil test kits are available through the Virginia Cooperative Extension Office in Fairlington and Master Gardener Plant Clinics. Virginia Tech’s soil lab will analyze the samples and e-mail you with the results and treatment recommendations within a week. (A routine test costs $10.)
Add organic matter
This helps improve drainage and lightens heavy soil. It also provides nutrients for soil microorganisms that help improve the soil. For new beds or vegetable beds, add compost and aged manure. A 2- to 3-inch layer worked into the soil is a good amount. Throughout the growing season, mulch all beds with organic materials such as grass clippings, shredded leaves, or additional compost. Since soil microorganisms literally “eat” organic matter, you can continually add organic matter to the soil.
Harsh weather conditions can pack down bare soil, so keep beds mulched with organic matter both during the growing season and over the winter. At the Library Garden, we liberally use Arlington County leaf mulch, which the County will deliver to your home. (Delivery of a full load–5 cubic yards–is $75 in Arlington and $50 for 6 cubic yards in Alexandria.) Mulching reduces erosion and weed growth, and moderates soil temperature and moisture levels. We do not recommend the use of wood mulch in your vegetable or annual flower beds as it can rob plants of nitrogen when mixed into the soil, but it is fine for pathways or as a light dressing around shrubs, trees and in natural areas.
Your fall leaves are good as gold. Don’t discard them. Shred them with your lawnmower and put them in garden beds like mulch or use them to make compost. All compost requires three basic ingredients:
- Browns: carbon-rich dead leaves, dry hay and straw, shredded newspaper, and cardboard;
- Greens: nitrogen-rich materials such as grass clippings, vegetable waste, fruit scraps, crushed egg shells, tea bags, coffee grounds and filters; and
- Water: which provides moisture to help break down the organic matter.
Note: We recommend against adding meat to your compost pile as the decomposition process can produce a foul smell that attracts flies, vermin, and neighborhood cats and dogs. It also slows down the composting process.
Turn your pile every few weeks, rotating the outside materials to the inside, and check moisture. Adequate water and warm temperatures will increase the rate at which the microbes work. Shredding and chopping the materials that go into your pile will also speed up the process. When it’s finished, your compost will be black and crumbly, like good soil, with a pleasant, earthy smell.
Plant a cover crop
I’ve started using cover crops in my vegetable garden and am a true believer. In late summer and fall, a few weeks before the first frost, I plant a “green manure” comprised of winter rye, field peas, ryegrass, crimson clover and hairy vetch. In the spring, I cut the crop before it seeds, let it dry out on top of the bed, and then turn it into the soil. After a couple of weeks, the bed is ready for planting. Cover crops provide erosion control and soil cover over the winter. They add organic matter and nutrients, and break up hard soils, improving the tilth.
The regular addition of compost, cover crops, and other organic materials to your garden can improve your soil to a point at which the need for additional fertilizers is greatly reduced. As you move through the seasons—pruning, dividing, staking, deadheading, cutting back and thinning your garden plants— pay attention to the soil. When you nurture your soil, you give your plants their best shot at producing flowers, foliage, fruits and seeds in beauty and abundance.