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Restoring Your Soil
“Mary, Mary quite contrary … How does your garden grow?" Even if the answer is “not well,” a black thumb might not be to blame. Instead, the culprit could be poor soil quality.
Good soil is the foundation of a healthy garden. As with a house, if you don’t have a strong foundation, you can expect a host of problems. In this case, those problems could be anything from lackluster tomatoes to drooping daffodils to watermelons the size of English peas. Start nurturing your soil now and expect a garden that turns your neighbors “green” with envy.
Testing, testing ...
How to find out if poor soil is to blame for last year’s sad squash crop? “If you’re having trouble growing and you’re not sure why, a soil test is a good place to start,” says Susan Littlefield, horticulture editor at the National Gardening Association.
Grace Gershuny, co-author of The Soul of Soil: A Soil-Building Guide for Master Gardeners and Farmers, says that county extension offices and land grant institutes often provide soil testing for a reasonable fee. You can also contact your state department of agriculture to ask about testing or recommendations for private soil testing labs.
“Even a home soil test will give you a reasonably accurate reading regarding pH levels,” Gershuny says. Many hardware stores or garden centers stock them.
Littlefield recommends that city-dwellers ask for additional testing for lead and heavy metals, which can leach into the soil from lead-based paints and industrial activities. “It’s especially important if you have kids,” she says. “You definitely want to know what’s lurking in your soil.” Although she usually discourages gardeners from purchasing new topsoil, Littlefield says it may be necessary to bring in new soil to create raised beds if the native soil is contaminated.
Once you’ve had your soil tested and know what you’re dealing with, you can get to work restoring or improving it before planting your garden.
A basic soil test will alert you to pH problems — soil that’s either too acidic or too alkaline. Soils in the eastern part of the country tend to be more acidic than soils in the West, where the arid climate creates alkaline soils, though Littlefield says that there is variation across the continent.
Most vegetables prefer soil that is slightly acidic, meaning it has a pH below 7.0. Some plants, such as blueberries, need especially acidic soil. To add acidity, Gershuny recommends gypsum (calcium sulfate) or elemental sulfur. Other options for increasing acidity include sawdust, composted leaves, wood chips, cottonseed meal and peat moss.
Soil too acidic? To create more alkaline soil (soil with a pH above 7.0), amend it with limestone (calcium carbonate) or dolomitic limestone, which will also add magnesium. Hardwood ash, bone meal, crushed marble or crushed oyster shells are other ways of increasing alkalinity.
Your soil test will usually come with recommendations of how much lime or sulfur to add to balance out soil pH.
No matter what your soil woes, adding organic matter can help. “Compost is the answer to everything,” Gershuny says. “The more you can get into your garden the better!”
Organic matter adds nutrients to the soil and can lower the pH to make it more acidic. It also supports healthy soil ecosystems by providing food for microorganisms that live in the soil. When these microorganisms digest organic matter, it “creates a glue that holds soil particles together,” which in turn promotes good soil structure, Littlefield says.
Proper soil structure is important for both sandy soils and dense clays. “Sandy soil is often too aerated, so nutrients run right through it,” Gershuny says. Organic matter can help the soil hold onto those nutrients. On the other hand, densely packed clays tend to suffer from poor drainage, so organic matter can provide space between soil particles for air and water to move more freely.
Kitchen scraps, cover crops and manure
Your kitchen compost bin is the best place to start on your search for organic matter, like vegetable trimmings, leftovers or those strawberries you never got around to eating. Littlefield says to avoid adding animal byproducts (meat, eggs, dairy), which break down slowly and attract pests.
If possible, create an outdoor compost pile where you combine your kitchen compost with leaves, yard trimmings, pine straw, wood chips, etc. Aim for a ratio of 2:1 brown matter (leaves and straw) to green matter (grass and kitchen scraps). Keep adding to the pile, turning it occasionally with a rake. “You’ll know your compost is ready when it becomes brown and crumbly and has a nice forest-floor smell to it,” says Littlefield.
Once the compost is ready, spread it on top of your garden plot, working it into only the top few inches of soil. Littlefield says that tilling or turning over your garden plot can actually damage the soil ecosystem, disturbing the soil structure and the microorganisms that live there.
“The less disruption you cause when adding compost the better,” Littlefield says. “Just spread it on top — earthworms and other organisms will pull the organic matter down into the soil. That’s how nature does it.”
Planting cover crops or “green manure” is another way of increasing soil fertility. Littlefield recommends planting annual or winter rye in the fall after harvesting your garden. Before planting in the spring, you can turn it over into the soil or pull it up and add it to your composter. Other popular cover crops include alfalfa, oats, buckwheat, field peas, vetch and legumes. In addition to adding organic matter to the soil, “green manure” crops also fix nitrogen in the soil and prevent weeds and erosion.
Finally, no soil fertility discussion would be complete without mentioning manure, another form of organic matter your garden will love. You can buy composted manure in bags from a garden center or beg a friend with cows or horses for fresh manure. For those truly committed to cultivating stellar soil, you can keep your own chickens, goats or other livestock for the purpose of harvesting their manure for your garden (think of the fresh eggs and milk as a bonus).
However, Littlefield cautions that fresh manure can be high in salts and too “intense” to spread on your garden immediately before planting. Instead, she and Gershuny recommend letting it age over the fall and winter so that it will be ready to use in the spring.
“It’s all about making the soil a better place for plants to grow,” Littlefield says.
More tips to save your soil
In addition to disturbing the soil structure by tilling or turning over the earth, Littlefield and Gershuny have a few other pet peeves when it comes to saving your soil.
- Avoid adding chemicals. “Chemical fertilizers and pesticides can be really hard on microorganisms, which are the key to healthy soil ecosystems,” Littlefield says. Gershuny adds that synthetic nitrogen can cause the same problems, plus the process used to make it is extremely energy-intensive. “There are things like blood meal, fish meal, alfalfa meal and similar products that will add soluble nitrogen if soil is very poor,” she says.
- Don’t tread on me. Minimize stepping where you plan to plant to avoid compacting the soil. Create pathways in your garden to walk on and make planting beds narrow enough that you can reach across them from either side when it comes time to harvest.
- Building blunders. Littlefield says that developers often scrape off topsoil from sites during building, leaving behind “really rotten subsoil.” If you’re building a new home, have your contractor stockpile your topsoil to spread back on your garden later, or rope off your garden plot ahead of time and ban bulldozers from that area. This will keep the soil from getting compacted by heavy machinery as well.
- Hands off when wet. We know you’re eager to get started, but avoid working in your garden when the ground is wet. “It can destroy the soil’s structure and turn it into a brick when it dries,” Littlefield says. How wet is too wet? Littlefield suggests molding a handful of soil into a ball with your fist. Flick it with your fingers — the ball should fall apart. “If not, it’s still too wet,” she says.