Enrich soil with natural amendments

You don't have to be a detective to choose organic amendments and use them successfully. Most natural amendments improve the soil's tilth and ability to retain moisture. Many of them make good mulches. Some have good nutritional value, although they may contain widely varying amounts of the three essential nutrients: nitrogen (N), phosphorus (P), and potassium (K).

By "natural" or "organic" soil amendments, we mean ones that are derived from living or once-living organisms, be they cows or worms, trees or other plants.

Commercially packaged soil amendments come from a number of sources, including the agricultural industry. Cattle and chicken ranchers sell manure to packagers. Farmers sell mushroom compost, rice hulls, and by-products from various other crops. Some cities collect and compost yard waste, then package it for retail sale or let residents pick it up free in bulk.

WHEN TO USE AMENDMENTS

Fall through late winter is a good time to dig or till organic amendments into your planting beds and borders. Work the amendments into the soil to a depth of at least 1 foot.

You can also spread a top dressing of 1 to 2 inches of amendment over established beds and just let it sit. When spring arrives, plants will push their way up through the mulch.

READ THE LABELS

When you're shopping for amendments, read the labels on the bags. Some manufacturers list the materials' nutritive values; others do not. And if the label describes the material as "ground," "screened," or "aged," you know you're getting something that wasn't just scraped off the floor of the barn and put in a bag.

As Don Knipp of Bandini Fertilizer Company puts it, "Grinding gives it a uniform texture. Screening sifts out rocks and big chunks. Aging allows the organic material to break down so that it doesn't rob the soil of nitrogen as it decomposes, and the animal urines have time to leach out."

One way to avoid using a manure that's too strong, or "hot," is to sniff the stuff. If the material has a strong smell of ammonia, let it sit in a pile for six weeks, turning it periodically, before you spread it on beds.

MANURES

Cattle manure (from steers and dairy cows) may contain as much as 1 to 2 percent nitrogen, 0.3 to 0.5 percent phosphorus, and 0.5 to 1 percent potassium. Dairy cow manure tends to have fewer salts than steer manure does. Well-aged manure is a good amendment for vegetables, annuals, and perennials.

Chicken manure is a rich, fertile amendment with nutrient values that can run as high as 3 percent nitrogen, 4 percent phosphorus, and 3 percent potassium. It can be strong-smelling. It can also burn plants, so don't use it on sensitive or shallow-rooted plants. If used properly, it gets annuals and vegetables off to a fast start. To avoid burning plants, spread it no more than 1 inch thick, and till it as deep as you can.

Guano and exotic droppings include bat guano, which typically has an N-P-K rating of 10-3-1, the highest nitrogen content of the amendments we list. Because of its potency, guano is the most likely to burn plants. Use it sparingly as a top dressing.

Some zoos collect and package manure from various animals. Elephant manure is the most commonly sold; the huge vegetarians produce a gentle substance that is on par with cow manure.

CONDITIONERS

Municipal compost is often made from grass clippings, leaves, and tree prunings gathered and composted by municipal agencies, then given free to residents or sold in packages or in bulk quantities. Compost improves soil tilth and water retention as it slowly releases nutrients.

Mushroom compost is a by-product of commercial mushroom farming that is low in nitrogen and phosphorus but quite high in potassium. It makes an excellent top dressing for roses. This alkaline amendment works best in areas where it is used to help balance acid soils.

Peat and sphagnum moss are great for holding moisture in the soil and loosening up dense soils. Peat moss increases soil acidity, so it's the amendment of choice for azaleas, rhododendrons, and other plants that thrive in acid soil. The moss is difficult to get wet initially. Suppliers suggest that you lay the plastic bag it comes in on its side, make a small slit in the plastic, insert a hose, and let it drip into the bag for a day or so before you dig the peat moss into the soil.

Redwood soil conditioner, made from the bark and sawdust of redwood trees and treated with nitrogen and iron, is a mainstay in California for loosening up hardpan soil. It decomposes slowly.

Worm castings are available packaged - or buy a vermicomposter and feed the worms vegetable scraps from the kitchen, then harvest the castings. Their nutritive value is low, but castings aerate the soil and improve its ability to retain and release nutrients.

Agricultural by-products such as rice hulls are usually available in areas where crops are grown. All are worthy amendments, provided they are well aged and don't have heavy concentrations of animal urine.

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