Soil Preparation

Soil Amendments


Our High Plain Garden naturally has a base of sandy loam. It has been augmented with compost provided for us by the Town of Andover DPW from the Bald Hill site opposite. Compost provides vital organic matter and nutrients to a sandy soil and helps to condition and break up soil with too much clay.

You can further improve your soil by using compost from purely organic sources. If you wish to buy one of the many types of compost from a garden center, please buy an organic product (ex., chicken or cow compost). One way of determining if the product is organic is the OMRI or Organic Materials Review Institute seal.

Soil Conditioners

Conditioners are best added before you plant up your garden in the spring. Generally, they are meant help retain moisture, increase aeration of the soil and improve soil structure. In previous years, I used peat as a soil conditioner in the past but no longer use it.

Advantages of peat moss:

  • allows for moisture retention in the soil

  • aerates

  • prevents soil compaction.

  • can last for years in your soil,

Disadvantages of peat:

  • slightly acidic; changes the pH of soil.

  • we are now being told that there is no safe or sustainable use of peat. Peat bogs around the world are being harvested more quickly than they can regenerate and the harvesting of peat releases carbon into the atmosphere. Left in place, peat bogs are carbon sinks that can absorb and retain more carbon than they release.

If you decide to use peat, one large bag per large plot is sufficient. I tried coir or coconut husks one year instead, as an experiment but also because of the environmental impacts of peat.

Advantages of Coir:

  • a renewable resource that ,as a soil conditioner, works on par with peat

  • pH neutral.

Disadvantages of Coir:

  • it is more expensive.

  • It can be dense and must be worked in thoroughly throughout the bed.

Loam ***the only soil addition that you need this year, given current conditions***

This is basic gardening soil that has (or should have) no additives, If will add a balanced mix of sand/clay/silt in roughly equal proportions. It holds moisture but drains well.

Other Amendments/Fertilizers

All plants need nutrients, both macro- and micro-nutrients, to thrive. You will see the macro-nutrients listed as nitrogen (N), phosphorus (P), potassium (K) on soil amendments sold in stores, but also others that do not figure in the N-P-K number such as, magnesium (Mg), calcium (C) and sulfur (S). Micronutrients are trace elements needed in much smaller quantities. As for the ratio you see in stores of N-P-K, the ideal ratio is 3-1-2 or multiples thereof. Again, these soil amendments are best done before you plant up your garden in the spring.

You can also buy a variety of concentrated liquid or granular organic plant foods at garden centers. These are amendments that you add mid-season.

However, soil at the older parts of the High Plain Garden is already rich, too rich in fact, and we ask that if you are in this area you do not add amendments that change the NPK balance in the soil , with one exception, nitrogen, see below.

At the Main Street Garden, potassium, in the form of potash, is needed in addition to nitrogen. In both the Main Street Garden and the new expansion of the High Plain Garden, you may add these fertilizers in moderation, as the soil is not over-enriched.

Bone Meal (an animal product)

  • increases phosphorus which promotes root growth & flowering of plants but too much phosphorus is bad for our water supply and of all the types of nutrients, phosphorus persists longer in the soil and therefore does not need to be topped up as much; generally using organics ensures that we don’t end up flushing large amounts of phosphorus into our water system.

  • adds calcium to soil; calcium increases the cell strength of plants and so prevents malformed or soft fruiting of tomatoes, etc.

Blood Meal (Animal) or Seaweed Meal (Vegetal) **Only additive needed at the community garden this year***

  • primarily increases nitrogen in the soil. Nitrogen allows for general growth of the plant, like healthy leaf development but too much stunts fruiting and flowering

  • Seaweed meal also increases potassium in the soil; potassium, like calcium, allows for strong flowering and fruiting

Worm Castings

If you have them, use them, as they are pretty much a perfect balance of the nutrients that a soil needs, plus they make soil more friable and less compacted. They can be added at any time. DO NOT introduce jumping worms into our garden. Use only paper vermiculture worm castings.