Along with the early daffodils comes really beautiful weather. It’s been sunny, the birds are singing…not too hot, not too cold. It’s time to prepare the soil. But first, we need to understand it.

 

 

Prepare the Soil

 

Herbs, vegetables, and flowers are going to be living—hopefully, thriving—in your garden for several months. For trees and shrubs, providing a good home will see them through the next decade, or the next century! It pays to give them the best conditions you can provide, and it all starts below the surface of the ground.

 

Axiom of the day: soil preparation is 90% of your effort.

 

If that sounds like work to you, you are correct! But you’re reading this presumably because past results have fallen short of expectations, and you want to improve your gardening skills. I’ve played in the “dirt” professionally for 50 years and can honestly assert: successful gardening depends on the health of the soil.

And here’s the good news. Thorough soil preparation will have benefits for many years to come. You won’t have to prepare the soil to this extent again.

 

 

The Soil Is Alive

 

Microbes

 

 

Soil is more complex than meets the eye. There is a dynamic interplay among minerals, organic matter, air, and moisture. Earthworms, insects, nematodes, and tiny microbes also contribute. Healthy soil is teeming with life! These organisms play an important role in how soil functions. Without them, organic matter would not break down into those vital nutrients needed by all plants.

Vast mycelial mats of beneficial fungi, or mycorrhizae, live in close association with roots. Millions—or perhaps a billion—species of these beneficial microbes inhabit soils around the globe, many of which live within or around a particular species’ roots. Researchers estimate that there could be a trillion species of microbes living in air, soil, water, and living organisms.

Soil-borne mycorrhizae have enzymes that can unlock, or chelate, micronutrients tightly bound to soil particles, making them available to plants. These organisms can gather water and provide it to plants even though the plants’ roots don’t have direct access to moisture. And these microbes act as barriers to certain soil pathogens.

Bacillus, Streptomyces, and Pseudomonas are common bacterial microbes. Fungal mycorrhizae, such as Trichoderma, Hebeloma, and Glomus help roots absorb water and phosphorus. Other microbes, such as viruses and archaea, also inhabit the rhizosphere, the area surrounding the roots. Gardeners are familiar with the nitrogen-fixing bacteria (Rhizobium) that increase yields in legumes.

Scientists have only recently begun deciphering the enormous number of microbes and what they do for or to plants. Only a few plant families, including Brassicaeae, do not have associations with fungal mycorrhizae. Blueberries and other plants in the Ericaceae family (azalea, rhododendron) have very limited associations with mycorrhizae.

Microbes benefit from the symbiotic relationship with roots by getting carbohydrates in return. The numbers of microbes inhabiting just a tablespoonful of soil are staggering. Believe it or not, that’s greater than the number of people living on the planet! Of course, not all of these microbes are beneficial; many cause diseases in plants and animals.

 

Tilth

Consider yourself lucky if your soil has good tilth, or friability, to begin with. Perhaps all you’ll need to do to prepare it is to add compost, aged manure, or some fertilizer periodically.

Soil stays more biologically active over a long period of time if it is not disturbed by frequent tilling. Beneficial fungi and nematodes are especially sensitive to major disturbances. Simply scratching products into the soil surface and watering them in preserves existing microbial populations in the soil.

There are several soil types distributed throughout the United States. They’re determined primarily by the kind of bedrock beneath the surface, the kinds of vegetation growing there, climate, and management practices employed through the centuries. Minerals from rock, eroded by water and wind, will be deposited downstream or downwind.

 

Soil Composition

Soil is composed of:

• mineral matter (rocks, sand, silt, clay)
• organic matter (carbon-containing [once-living] compounds such as compost, aged manure, dead roots, dead organisms). Never use fresh manure; the ammonia content can harm plants, and it might harbor pathogens.
• living organisms (such as earthworms, nematodes, microbes, insects)
• air
• water

Tilth and fertility are determined by relative proportions of these materials. All kinds of soils benefit from the addition of compost and other organic materials. I confess to going a little overboard on these amendments when I prepare the soil. But the plants look great!

You might be fortunate to start with soil that has good tilth. It already has physical characteristics which promote plant growth. Or experience indicates that the roots will need some encouragement to grow beyond the original root ball.

Soil that is a rocky clay, for example, dries to the consistency of brick, and will need lots of amendments to improve drainage and to encourage roots to grow vigorously. On the other hand, sandy soils need materials that will improve water and nutrient retention. Instead of repeatedly failing with plants that can’t adapt to your soil, try starting out with those that can. Working the garden over the years will condition the soil sufficiently so you’ll be able to grow more species.

 

 

Simply digging a hole in the ground, adding a cupful of compost, and plopping the plant in place won’t do the trick in heavy clay or rocky soils. Depth of topsoil, drainage patterns, ratio of clay to organic matter, air pore space (the space between particles), and, of course, fertility and pH, all enter into the equation.

The rich, black ground in our West Virginia garden needed no amendments at all; the foxgloves grew 7 feet tall! Still, I added organic matter every time new plants went into the ground.

 

 

From Awful to Awesome

 

First, the Awful Bit

Our first house in Maryland sat on the crest of a hill. Sunrises and sunsets were spectacular, but the soil was just awful. It was all clay and shale. Any organic matter that did exist blew away or washed down the slope. That “dirt” refused to yield even to the most enthusiastic shovel.

I created a vegetable garden farther down the slope, next to the greenhouse, that gave us fabulous crops of tomatoes and peppers. Digging in autumn leaves, vegetable scraps from the kitchen, and discarded material from my horticultural business greatly improved the soil. It didn’t take long for decomposition to begin and for the earthworms to show up.

 

 

 

Almost Awesome

A few years later, we moved farther south to a community that had been carved out of an old oak and hickory forest. Although the soil quality was better here than at the previous property, I continued to prepare the soil with every new project for the next 3 decades.

Before planting rhododendrons (like the one in the photo, below) in the afternoon shade, I added peat moss and pine fines to the soil. These materials were not merely thrown on top of the ground. Instead, generous quantities of amendments were incorporated (not layered) into the top 12″ to 18″ of existing soil. Then, I mixed nutrient-rich LeafGro (locally sourced compost) into the top 8″ of loosened soil.

This effort created a well-balanced mixture, composed of existing clay and loam, and the added peat moss, composted pine bark, and compost. After that, the soil remained undisturbed except for top dressings of fertilizer, compost, or mulch.

 

 

I left the ditch behind the shrub border undisturbed, allowing rainwater to travel down the slope. Water that did not drain away would have meant death for the shallowly rooted rhododendrons.

Blueberries must have very acidic conditions, in a range from about 4.3 to 5.3 pH. Rhododendrons, azaleas, and hollies like their pH a bit higher than that, but still on the acidic side. Peat moss and pine fines incorporated into the soil helped provide the acidity and aeration.

 

 

Petunia, calibrachoa, pansy, and viola also benefit from a lower (acidic) pH. Plants growing in soil with closer to neutral pH will have sickly yellowish leaves with green veins (photo, above).

 

A Shady Oasis

Gradually, most of the back yard grew into a private woodland. Japanese snowbell (Styrax japonica), paperbark maple (Acer griseum), Pieris, Abelia, Viburnum, Kolkwitzia, and a group of monarch birches (Betula maximowicziana) were the main players. And the rhododendrons and existing vegetation, of course.

Mulched pathways meandered under the cool canopy, and all sorts of shrubs and perennials luxuriated in that rich soil. There was a small pond, a greenhouse, and no grass to mow in the back yard. Awesome. (***Update***: As it often happens, subsequent owners of the house altered the property to suit their needs and removed almost all of those plants.)

 

 

Monitor Soil Health Over Time

 

Preparing the soil for vegetables is not difficult, and the results will last for years. Most varieties prosper in improved soil 10 to 14 inches deep. Lettuce and radishes need only 5 or 6 inches.

Using the space efficiently and intensively calls for carefully managing the soil. Vegetables grow quickly, fruit heavily, and, therefore, require frequent additions of nutrients. 

Thoroughly preparing the existing soil will pay dividends, spelling the difference between getting a few vegetables from the garden (“Why bother?”) and having a truly abundant harvest (“Take some veggies, please!”). And, if you properly prepare the soil at the start, you’ll never have to repeat the effort to that degree.

Keep in mind, though, that, as organic matter breaks down and is absorbed by plants and other living things, you’ll need to add more compost. For top performance, plants need balanced fertilizers that are appropriate for specific uses, such as for vegetables, flowers, spring flowering bulbs, or the shrub border. That’s in addition to the compost or aged manure you originally used to prepare the soil. Lack of nutrients and compacted soils are among the top reasons for low crop yields.

 

Soil Testing

Contact your local Master Gardeners program, or the agricultural extension office, for information on soil testing. The results will indicate which amendments to add, and whether the pH is appropriate for the plants you want to grow. The report also includes a breakdown of the soil components: clay, silt, sand, and organic matter. Normally, I add more organic matter than soil tests recommended.

Soil pH is a measure of acidity or alkalinity. Neutral is 7.0, with acidic values below that and alkaline values above 7.0. A simple soil test will indicate pH and nutrient levels. Soil pH affects the availability of nutrients to plant roots, with most vegetables preferring pH levels between 6.0 and 7.3.

Years ago, a landscape client wanted to prepare the soil for a vegetable garden on the property she and her young family had just bought. She expressed concern for “bad things” in the ground, so I suggested that she ask for a lead test in addition to the basic tests. The cost of the basic test is very reasonable, but extra requests will raise the fee. No matter; it’s worth the cost.

The report showed a surprisingly high lead content in the soil, unusual for a newer home. So, you don’t want vegetables growing there! She submitted tests from different areas, and felt confident that the original spot was unique. Something probably had been dumped there before the house was built. Later, the family was going to have the contaminated soil professionally removed.

Lead Paint

In 1977, the Consumer Product Safety Commission banned the use of lead paint in residential properties. If you live near an industrial region, a busy highway, or where lead paint might be a concern, I strongly advise testing for lead before you prepare the soil. Local zoning authorities should have records on past property use. For more information, contact the National Lead Information Center at 800 424-5323.

Lead poses a serious health risk, especially to young children. There is no level of lead that is considered “safe enough”. And most of us grow our own vegetables for the health benefits, after all.

For now, gather your tools and your help, and pace yourselves. This is not something to be accomplished in the hour before your daughter’s softball game. So, you might as well turn it into a party—arrange for pizza delivery at the end of the day! You certainly will have deserved it.

 

 

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