This year’s soil test


We try to run general soil tests on the gardens every three years or so. This summer we tested samples separately from 1) across the “old raised beds,” 2) across the “new raised beds,” and 3) from the pile of new soil under the tarp near the shed. [The site soils in the Heritage plots and beneath the lasagna plots were tested previously, and should have improved since the introduction of lots of organic matter over the last few years. We can test those next year again.]

In general, there was not a great deal of difference among the three different areas, so this report will deal with them all together. Complete soil test results will be posted in the garden shed.

The good news is that levels of lead are very low throughout, levels of macronutrients (phosphorus, potassium, calcium, magnesium) are high throughout, and levels of organic matter are high. The take-away is that you do not need to add any phosphorus, potassium, calcium, magnesium, or nitrogen to your garden. It is very likely that micronutrients are not an issue either, since compost generally contains plenty.

Nitrogen is an element that moves rapidly and is not usually tested for. Given the plant growth we are seeing, nitrogen is being supplied in adequate quantities by the organic matter and by any plants you are growing that help increase N-fixing bacteria (peas and beans in particular).

For the growth of most vegetables, the pH is mildly on the high side (more alkaline, less acidic). This can affect a plant’s ability to access nutrients and micronutrients, which can become a real issue. The bad news is that some composted material can have a higher pH, and I think this includes some of the compost that has been mixed in with our raised-bed soils. The good news is that nature in New England will correct this issue over time and lower the pH. You could speed this along by adding some of the more acidic amendments and mulches, such as peat moss and pine straw, or sulfur products intended for that use. The main take-away is that you definitely should not add anything that will raise the pH. This includes lime, dolomite, wood ash, bone meal – all of which raise the pH.

Now, back to the soil we’ve been importing to build our raised beds: we order a mix of clean loam soil and compost as a good “starter-kit” for creating a healthy soil ecosystem. This takes time. As the compost continues to break down in the soil, the bacterial and fungal decomposers utilize nutrient elements that would otherwise go to plants. As a result, sometimes plants will show nutrient deficiencies. The gardener needs to keep replenishing organic matter until the decomposers and the new organic materials and the growing plants come into a balance. Initially this may take a year or three. The main take-away is to begin managing your soil ecosystem by continually adding small amounts of organic matter. This could be a straw or hay mulch (careful of importing weed seeds!), fall leaves (preferably shredded), finished compost, pine needles, or other.

To summarize:

In general, the beds do not need any nutritional help. Fertilizer can actually be a negative.

Do not add anything that will raise the pH (increase the alkalinity). Materials to avoid include lime, dolomite, bone meal, wood ash.

Actively manage your soil ecosystem by adding organic mulches and topdressings.