Amendment is a broad term and can include organic matter such as composted manures, wood mulch, peat moss, or kitchen compost. Organic amendments break down over time and need to be replaced. I think of it as feeding the soil rather than feeding the plants. By improving/amending the soil, plantings are better able to develop a vigorous root system. Typically my landscape includes clay in the low areas, sandy loam in the higher areas, and topsoil where the soil has been left undisturbed or was piled when we had excavation work done before building. We did not build or put driveways on topsoil. Avoid disturbing an area until you are ready to begin working/planting it; once the ground is disturbed, it becomes a natural site for dormant weed seeds to develop.
One frequently asked question is whether to amend the planting hole or the whole bed. My quick answer is, the whole bed. By improving/amending the soil of the entire bed, the plantings are better able to develop a vigorous root system. This applies to beds, borders, hedges, vegetable gardens, and turf areas. When you are ready to amend the soil, it is important that you work when the soil is neither too wet nor too dry. Clay soils compact easily, and working the ground when the soil is too wet will cause serious, long-term damage. Likewise, working dry ground (hurts my back just thinking about it) is simply too difficult to till or spade by hand. We till the top six inches of the entire garden area, add amendments, then bring those tines up and till the amendments into the top four inches. When bringing in topsoil for raised beds, we recommend gardeners level and water the new bed twice over 10-14 days so the new soil has a chance to settle before planting. We have had to bring in additional topsoil to bring the level up to where we want it. Once the desired level has been attained, it is certainly easier to incorporate amendments prior to planting and the additional effort will pay off in the long run.
The amount of conditioning you do to your soil is clearly tied to the expectations of the area. Most gardeners appreciate the importance of topsoil but have little understanding of the need to continuously add soil amendments. Plantings take from, not add to, soil quality and unless replaced, nutrients are quickly exhausted. I enjoy gardening and am willing to topdress gardens with organic amendments and slow-release fertilizers every fall, after the perennials have beed cutback, to ensure quality growth next spring and summer.
Characteristics of clay soil:
• Holds water
• Poor drainage
• Contracts (cracks) when dry
• Compacts when wet
Simple tests you can perform to check on the condition of the soil when considering an area for new development, or to troubleshoot for problems in an existing garden:
1. Half-fill a clear, quart jar with soil then fill to the top with water, thoroughly shake then let sit overnight. Sand sinks and represents the bottom layer of the mix, silt is lighter and will reveal itself in the middle layer, clay will be towards the top, and if the soil has organic matter, it will be at the top. The water can be used to perform a simple pH and fertility test using an at home test kit.
2. While the soil is evenly moist, squeeze a clump in your hand, if it breaks up easily, great, if it forms a solid clod, it's clay.
Amendments for soil fertility are simply called fertilizers and include the major elements nitrogen, phosphorus and potassium. These elements are represented by three hyphenated numbers and are usually combined with trace (minor) elements and are essential to healthy plants. I apply a slow-release 14-14-14 fertilizer with trace elements along with granular iron in the fall after the perennials have been cutback. I also apply fertilizer in any newly planted gardens developed through the summer months. Application rate is 1 pound per 100 sq. ft. of garden area. I use a hand held spreader and apply to all plantings including trees, shrubs, perennials, and annuals. Slow-release fertilizer is temperature activated and the fall application ensures the nutrients will be available for the plants next spring.
I also apply a water-soluble fertilizer about mid-July. I use a 20-20-20 solution and apply with a hose end sprayer. This gives my perennials and annuals a quick boost for mid-summer color. Without the use of a slow-release fertilizer, I would have to make several applications of water-soluble fertilizer throughout the growing season.
Soil amendment checklist:
• Determine existing soil conditions
• Replenish organic matter every year
• Fertilize on a regular schedule