2009-01-15 / News

Gardening 101: Nutrients

The Island Garden
By Roger Marshall

This year the editor and I thought we'd bring you something a little different for a gardening column. Beginning this month we'll be looking at all that is involved in planting your own vegetable garden to grow your own organic food.

The premise is simple: You can start a garden - even those of you who consider yourselves to have a "black" thumb - and successfully grow produce that is fresh, nutritious, pesticide-free, and doesn't cost two or three dollars for a single head of lettuce. So, if you've never gardened before, you might want to cut out these columns and keep them until early spring when you can start working your soil.

We'll start with the basics. You probably learned in elementary school that plants need four things to grow: nutrients, light, warmth, and water. Your garden soil provides the nutrients, the sun provides the light and the warmth, and the water comes from rain or from moisture that you supply in times of drought.

We'll look first at making sure that your plants get all the nutrients they need. This is particularly important if you want to garden without heavy use of pesticides. In this case, you need your plants to grow and control the insects so that they won't be able to eat them all before you do.

Unless you want to grow hydroponically (that is, with the plant roots in water), you'll be setting your plants in soil, from which they'll derive all the nutrients they require. But like any other nutrient source, soils become depleted over time, so it is up to you to make sure that the necessary nutrients are maintained at adequate levels. For one thing, your soil needs to contain sufficient amounts of the macronutrients nitrogen (N), potassium (K), and phosphorous (P). If you look on the side of any box of commercial fertilizer, you'll see the N, K, P numbers telling the amounts of each of these elements that the product provides. Many gardeners are happy to rely on an all-purpose commercial fertilizer to feed their plants throughout the summer. But these fertilizers do nothing to build the physical structure of the soil. This is why many other gardeners prefer to obtain their soil nutrients from various organic materials such as compost, well-rotted manure, feather meal, bone meal, dried blood, kelp, greens, and rock phosphate. You can add all these nutrients by making your own compost, or you can buy compost at a garden center. Compost is simply wellrotted organic matter. (We'll look at making your own compost in a later column.)

Your first step in making sure that your garden soil has sufficient nutrients is to take a sample of the soil you intend to use and get it tested. This can be done by sending the soil sample to the URI Cooperative Extension Service using the form provided at http://www. uri.edu/ce/publications/soiltest. pdf. Just follow the form's instructions. The standard soil test that screens for both pH (your soil's acidity level) and the extractable nutrients should be adequate for your needs, although for just a few dollars more you can also test for the organic matter contained in your soil. After sending your soil off for testing, you will receive back recommendations as to what you need to add to it and in what amounts.

For example, let's say that your soil is heavy in clay, which means that it is dense and retains a lot of water. It will need to be lightened considerably to allow water to adequately drain from it and also to enable the roots of plants to penetrate the soil. In this case, you'll need to dig in (or rototill in) lots of organic matter and sand. Getting good soil from heavy clay might take two or more years of work to achieve.

Frankly, I'd take an easier and quicker route to good soil. On a heavy clay soil I'd build a raised bed and fill it with fresh loam, sand, compost, and other organic materials so that I could start growing plants immediately. As its name implies, a raised bed is raised above the surrounding soil level with some form of retaining wall. Its big advantage is that it can be filled with soil the quality of which can be controlled fairly easily. You can also put this technique to work in an area where you want to expand into next year. Into a newly built raised bed simply layer dead leaves, untreated grass clippings, shredded plant stalks, rain washed seaweed, and anything organic that comes out of your garden, cover everything with a layer of soil, and leave it all to rot down. In a year or so, when everything is fully decomposed, you will have nice, freshly formed loam into which you can set your plants.

It might take a few years to get good tilth in your garden - that is, soil that is deep, dark, crumbly, and easy to plant in. But once you have achieved this goal, your plants will love it and reward you with lots of produce.

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