We call ourselves dirt gardeners because we are happiest in our gardens. But what we have underfoot isn’t dirt, but soil. The difference is good soil is a rich, living medium in which our plants can grow healthily and happily. And dirt is… dirt. The trouble is that few of us come naturally by good soil. We have to make our own.
The faults of New England soils are well known. They are rocky or sandy. They were worn out by early colonists and scraped off by developers. Too often we have fed them a steady diet of chemicals designed to make our grass, flowers, shrubs or trees grow faster and kill off everything else. We’ve conscientiously removed grass clippings and autumn leaves as if they were enemies and not friends.
Healthy gardens start with healthy soil. Healthy soil is a mixture of minerals (ground up rock), organic material (the remains of things which were once living) and lots of living creatures. Very few of the creatures are large enough for us to see. Earth worms are the godzillas of the soil. Smaller are ants, beetles, and other insects. And visible only under microscopes are bacteria and fungi that by weight and volume are the largest living component of our soil.
Our larger guests help to keep the soil aerated. The smaller inhabitants are the hardest and most valuable workers. They break down organic and inorganic materials into their constituent parts, making those nutrients available to the plants. They
form symbiotic relationships with the roots—trading their ability to supply raw materials for a small amount of the plant’s food.
The minerals or inorganic part of our soil are present as sand, silt or clay. Sand with its relatively huge particles makes poor gardens because it cannot hold the water or nutrients needed. Silt is substantially finer, much better at providing what a plant needs. Clay is so fine that the particles compact together not allowing water or nutrients to flow through to the roots. Every type of soil is improved by the addition of organic materials—be they compost, peat moss, chopped leaves, and so forth. If you buy soil, remember there is no standard for what is sold as top soil or loam. You must ask for an analysis of the soil showing the percentage of sand and silt and organic material. Any soil less than 5% organic matter is not healthy soil.
An inexpensive soil test can tell you a great deal about your soil. First of all the pH, or acidity of the soil. In New England, all soil is acidic, the question is how acidic. Most plants, and beneficial soil organisms, grow happily between 6 and 7. Some of our favorites such as rhododendrons and evergreens, prefer a lower pH 5 to 5.5. Left untreated, soil in NE, derived from acidic granite, drenched by acidic rainfall and feed with acidic fertilizers can drop well below even that. And if the soil is too acidic, many nutrients can not be taken up by the plants, others such as iron become toxic.
Fixing the pH of your soil is the one of the easiest garden tasks. Simply spread lime over the soil on existing beds and dig it in to new beds as you create them. But how much lime do I put on? The soil test that you did before you started will tell you. You can put lime down at any time of the year—even over snow, but try to keep at least a week between liming the area and fertilizing. Lime speeds up the release of nitrogen more than you want.
Compost is the black gold of gardening. When made from clean (not diseased) plant material or fully decomposed animal manures, it can only benefit your garden. Compost adds organic material, improving the structure of any soil it is added to. It provides a wide variety of nutrients and a healthy population of microorganisms that benefit the plants. Worked into the soil before planting it provides an excellent starting point for a healthy garden. Added as a mulch on top of an existing lawn or garden it may take longer but nevertheless improves the soil.
Mulches benefit both your plants and your soil. Mulch prevents erosion, conserves water, moderates soil temperature, inhibits weeds and can help prevent soil compaction. Organic mulches—wood or bark chips, straw, grass clipping, shredded leaves and so forth, break down over time and improve the soil.
Beware of colored mulches. At a recent conference, Bill Cullina warned attendees that many colored mulches are made from used wood such as old pallets. Not knowing where the wood has been or if it has been contaminated, makes these a bad choice. And inorganic mulches may have some purposes, but eventually weeds will grow up through stones, rubber mulches will leach toxic chemicals, plastic sheeting will tear.
Plants do not know the difference between organic and inorganic fertilizers, but your soil will. Repeated applications of fertilizers, especially those combined with herbicides (Weed N Feed) or insecticides (Weed N Kill???) will kill the micro-organisms in the soil. Over time soil will become sterile, plants will require more and more fertilizer to grow. Inorganic fertilizers can be used to supplement the nutrients supplied naturally in healthy soil. But this means and taking the time and care to use fertilizer only when and where and as needed.
There are thousands of types of soil. What they all have in common is that we can make them better or worse for growing plants by the way we treat them. Leave your grass clippings on the lawn and they become fertilizer, not trash. Mow leaves into the lawn and they too quickly break down into compost. Make compost from your garden debris and use it to pay back the soil for its never ending work of hosting your gardens.