How to Use Compost

Use this plant-by-plant guide to take advantage of all the benefits your garden can gain from compost − a fantastic all-purpose amendment that offers plants a nutrient boost.

By Stu Campbell


November/December 2016

Composting In The Garden

Many expert gardeners use compost as their only form of mulch.

Photo by iStock

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Compost is one of the most important and versatile tools available to gardeners. In fact, many expert gardeners use compost as their sole garden amendment and in turn reap abundant harvests of organic vegetables and fruits. Compost is easy to use, yet some of us may not be sure exactly when and how to use compost on our garden plants. This plant-by-plant guide outlines the best ways to use compost in your garden to achieve your own healthy harvest. Compost gives us a way to recycle food waste back into the earth, and get delicious, nutritious food in return. What’s not to love?

Compost Basics

The most advantageous time to incorporate large volumes of compost into the garden is the late fall. This is the time to spread whatever compost you have made during the summer over the entire growing area. You can do this any time after the first killing frost and before the soil freezes hard. It is not a requirement that it be turned or tilled; you can let it lie there over the winter. If you want to do the garden the most good, mix the compost in with the soil.

You can also add finished or nearly finished compost about a month before planting time in spring. At any time of year, you may add completely finished compost as mulch — especially in the hottest, driest periods of summer.

If you plan to make new raised beds, make the job easier by incorporating compost thus: Mix a 2-inch layer of compost into your soil. Then mound the soil into raised beds 8 to 12 inches high and 3 to 4 feet wide.

Compost for Popular Plants

All plants benefit from compost worked into the soil — from seedlings and potted plants to garden crops, shrubs and trees. The best additional applications of compost for some popular garden crops are outlined here.

Mixed annual flowers and vegetables: As part of routine maintenance, mix 2 inches of compost into soil to a depth of 6 to 8 inches. Also add compost as a side-dressing to give plants a boost periodically throughout the season, especially in late spring and then a month or two after new plantings.

Tomatoes: When I get ready to transplant, I dig a furrow 4 to 6 inches deep and fill it halfway with rich compost before planting the young seedlings with their long stems lying sideways down in the furrow. The stems, fed by rich compost, start to grow tiny root hairs almost immediately, and within a couple of weeks the stem transforms into a long and complicated tangle of roots — a strong foundation from which the plant can grow healthy and well-nourished.

Peppers: I usually transplant in the same row as tomatoes, interspersed as companion plants. I set their stems upright on compost, not lying down.

Pole beans: Dig a row of holes about 3 feet apart, 8 inches deep and 2 feet in diameter. Then, with a crowbar, poke a much deeper and smaller hole and set the bean pole — a straight stick 7 or 8 feet long — in the center of the larger hole. Fill the bigger hole with a compost and fertilizer mixture and lay a circle of seeds right on top of the compost, keeping each seed about 8 inches away from the pole. Set a ninth seed in the middle, next to the pole, add about an inch of loose soil over the top and tamp it down by hand.

Corn, cucumbers and squash: I use the same technique as for beans, leaving out the pole, naturally.

Peas, beans, grapes, lettuce, cabbage, cauliflower, broccoli, raspberries, Brussels sprouts, chard, spinach and other greens: You can plant these crops in compost. It takes a bit longer than planting or transplanting the conventional way. Make a shallow trench or hole with a hoe, shovel or furrower. Put compost in the depression, then lay the seeds on the compost. Cover them and firm the soil.

Grapes and berries: To nourish established fruits, cover soil around plants with a 3-inch layer of compost mulch in early spring. The mulch will act as a weed barrier and also feed the plants.

Strawberries: Build a little mound of compost in the bottom of a shallow furrow and drape the roots of the young plants over the mound so they cover it like a skirt. Then bring the soil up to the plant just below the crown. 

Newly planted perennials such as asparagus and rhubarb: Plant them on top of a trench 8 inches wide and 1-1⁄2 feet deep filled with a mix of fertilizer and
compost. To add compost to established perennials, gently mix a 1- to 2-inch layer into the topsoil or apply it on top as mulch. Trying to work compost deep into the soil may damage tender roots.

Shrubs and trees: Spread 1 to 2 inches of compost around plants and work it gently into the surface of the soil. Then cover with a mulch of cocoa hulls or bark chips. Fruit trees like compost applied in a circular band around each tree, starting 2 to 3 feet away from the trunk and extending to the drip line at the ends of the branches. Use 1⁄2 to 1 inch of compost annually, or add a 3- to 4-inch layer, which will last as many years. Cover compost with a mulch of hay or grass clippings.

Acid-loving plants such as rhododendrons and blueberries: Apply an acid compost, made by using oak or beech leaves, sawdust and pine needles in your compost.

4 More Ways to Use Compost

Seedlings: Make your own planting mix for seedlings with 1⁄3 screened compost, 1⁄3 soil and 1⁄3 coarse sand, perlite or vermiculite. This mixture will supply young plants with all the nutrients they need until transplanting. Compost provides a slow release of nutrients as opposed to inorganic fertilizers, which can burn seedlings initially and then cause nutrient deficiency all in a matter of weeks.

Potted Plants: To make potting soil for indoor plants, strain it first to remove clumps and debris, then mix about 1⁄3 compost and 2⁄3 soil and it’s ready for planting. Add a pinch of compost on top as mulch and your plants will get nutrients every time you water.

Mulch: Screened compost makes a handy mulch around closely spaced vegetable and flower plants. If you have an abundance of compost, you can afford to be generous with it as mulch. But if you never have enough, you’ll get the most benefit out of mixing it into your soil.

Lawns: Well-decomposed compost can be incorporated in the soil when planting a new lawn. Spread a 2-inch layer over the area and till it in before seeding. An established lawn will benefit from a top dressing of finely screened compost. Apply it in spring or fall after aerating your lawn.