Chapter 4: Soil Amenders

Soil preparation and its improvements provide more benefits than any other gardening practice.  The better your soil, the better your gardening results will be.  Not only will you grow a larger harvest, you'll grow healthier plants which in turn resist insects, pests and diseases. By using a Raised Garden, which allows the gardener to concentrate efforts to improve soil composition in a small area, good growing soil can be achieved in less time with much less labor than it would take to attain good soil in a traditional row garden.

The following soil amenders will help you create and maintain a healthy soil for your Raised Garden.

Compost
Known as "Gardener's Black Gold," compost is the backbone of a rich, friable soil.  The end product of decaying organic matter, humic acid, gives soil its dark, rich color, enhances bacterial action, increases nutrient holding capacity, improves drainage, and acts as the cement which holds soil particles together as well as apart.  Compost, available in 3 cubic foot bags from most garden and home centers, is also available in many communities from compost recycling operations.

To make your own compost, construct a compost bin in your garden where garden and kitchen refuse can be recycled.  A bin can be made with our Anchor and Stacking Joints, or purchased as a prefab kit from home and garden centers.  The secret ingredients for successful composting include a balance of organic matter, moisture, oxygen, and bacteria.  The organic matter includes everything from the yard and garden except tomato, eggplant and pepper foliage and stems, and cucumber, melon, and squash leaves and vines.  These plants may contain diseases which you do not want to add to compost or soil.  Grass clippings, fallen leaves, and even small twigs can be composted.  Kitchen scraps like lettuce and cabbage leaves, turnip peals, carrot scrapings, coffee grounds, and egg shells may be added to the compost pile.  Do not add bone, grease or meat drippings as they can draw rodents. 

To decompose organic matter (the smaller the piece, the better), bacteria, moisture and oxygen must be present.  To each new layer of organic matter added to the pile, spread several shovels full of garden soil (soil contains the needed bacteria to inoculate the organic matter) over the layer and add water to thoroughly moisten the organic matter.  Turning the pile will speed decomposition but is not absolutely necessary.

 Peat Moss (Sphagnum Moss)
Sphagnum peat moss is a renewable resource which is the decomposed remains of sphagnum mosses and other bog plants that have been compressed for thousands of years at the bottoms of bogs and swamps.  It is decidedly acidic, normally in a range of pH 3.5 to 5, holds moisture well, provides bulk to soil mixes, is fairly lightweight and relatively inexpensive to buy.  Peat moss betters the structure of clay type soils by improving aeration and slowly releases moisture, important in light, sandy soils. 

Manure
A gardener's best friend, manure enriches soil with organic matter and provides small quantities of nutrition.  It releases its nutrients into the soil on both an immediate and an extended basis, helping crops grow steadily throughout the season.  Raw manure, taken straight from an animal should be composted or prepared in soil 3-6 months prior to planting so not to burn plant roots. 

Dried or Dehydrated Manure
Commonly purchased in bags at home and garden centers and nurseries, dehydrated or dried manure can be worked, as is, into the soil.  Planting of seeds and transplants can begin immediately without burning of plant roots.

Perlite
Perlite is pure white, gritty, porous heat treated volcanic rock, sterile, and essentially neutral in pH (7.0 to 7.5).  With such characteristics, perlite is used to improve aeration and drainage of potting and planter mixes and other poorly drained soils.  It does not deteriorate or decay in the soil.  Perlite is available bagged by the cubic foot from home and garden centers.

Vermiculite
Vermiculite is a mica-like ore subjected to very intensive heat until it expands forming thousands of layers of a porous material.  It is lightweight and works well with all soil types, tremendously improving soil's friability and capacity to hold water.  It is not recommended as an additive to poorly drained or naturally wet sand.

Sand
Sharp or coarse sand (not beach sand as it may contain salt) is incorporated into raised bed mixes or freestanding garden soils to improve drainage and aeration.  Bagged coarse or sharp sand is available from builders supply and home and garden centers.

Lime
Lime is used to correct acidic soil conditions.  It is applied to soils to raise soil pH.  While most vegetables grow best in slightly acidic soils, too much lime can make the soil too alkaline thus reducing the availability of some nutrients and retarding plant growth.  Before adding lime, consider all other alternatives to enriching your soil and test its pH content prior to adding.

Lime is available as ground limestone, pulverized limestone, and pelletized limestone (pulverized limestone particles which have been glued into a manageable size.)

Sulfur
Has the opposite effect of lime on soil, sulfur is used to lower pH of soil.  Again, before adding sulfur to your soil, test the soil pH to see if its pH is too high and then add accordingly.

Dried Blood
Features a high concentration (9-14%) of readily soluble nitrogen, quickly available to the plant.  The usual rate of application, 2 to 3 lbs. per 100 sq.ft., also acts as a rabbit repellent.

Kelp Meal
Kelp is a nutrient-rich form of seaweed.  It supplies over 40 major and micronutrients, improves soil texture and tilth, helps retain moisture, and improves resistance to pests and diseases.  Kelp meal should be incorporated into the soil during the fall for benefit during the following growing season.

Greensand
Glauconite, a rich source of over 32 micronutrients, loosens clay soils and improves water and nutrient retention in sandy soils.  An excellent but somewhat expensive source of potassium. (0-0-7)

Gypsum
Provides a source of calcium and sulfur for soil without changing the soil pH.  Gypsum is recommended for application to poorly drained soils to improve aeration and drainage.

Wood ashes
Applied sparingly, wood ashes are a rich source of calcium (acting similar to lime in adjusting the soil pH) and provide a soluble source of potash.  It also supplies micronutrients.

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