AboutMike Mascio Expertise I have been an avid gardener since 1985 and an AllExpert volunteer since
1998. I specialize in soil preparation, seed starting and plant
propagation, flowers, vegetables, and general landscaping. I am a strong
advocate of the square foot method of gardening and the use of organic
controls for pests and diseases.
Question Hi, I need advise about whether to amend a 1 foot deep raised bed of well composted horse, cow and sheep manures. Do I need to mix top soil or anything into the raised bed?
Here's the Maine State soil testing results for my garden and field:
The field on which the rows sit has a pH of 6.5 and optimum levels of Phosphorus and Potassium. Calcium is high (3544), and the Maine state testing service recommends I add nutrients to boost nitrogen, magnesium, sulphur and organic matter, all of which are in the medium range (less than optimal).
In half of the garden, I did mix the composted manure with the soil, and the levels for each major chemical tested exceeds optimal levels (phosphorus, potassium, calcium, magnesium, sulphur all very high, and soil pH is 7.7). Organic matter is in the optimum rage. The state testing service suggests only that I add sulphur to lower pH.
In the foot deep, composted manure, every chemical tested again exceeds the optimum range, but the only instruction was again to get the pH down. Levels of Potassium (346), Magnesium (1760) and Magnesium (13.2) are noticably higher than in the row with manure and soil rototilled together.
Is it problematic when P, K, Ca, Mg and S exceed optimal levels like this? To get the best production, should I just adjust pH, or mix top soil or something else into the composted manure? Thanks so much, Dick Thomas
Answer Dick, it sounds like all you need is sulfur to reduce the ph level to near 7.0, but I would not get too caught up in all of the various nutrient levels. Although a neutral soil of 7.0 is ideal, the results are far from a perfect science.
I find that as long as I amend the soil every fall and spring with an even mixture of carbon materials and nitrogen matter, the ph level stays fairly stable. I simply add compost, peat, dried grass clippings, and shredded leaves. If the level falls below 6.5, I add lime; above 7.5, I add sulfur. During the summer, I keep two large compost piles; one caged and open for larger items that have yet to break down; and one in a closed bin that has materials that are in the latter stages of the process. By fall, I have enough compost to fill my raised beds back to their full capacity.
Personally, I never add topsoil to my beds. I only add compost, aged manure, and peat. Natural leeching from rain keeps the nutrient levels balanced. If the ph levels rise, avoid composting with acidic materials such as pine needles. But as I've learned over the years, unless the ph is extremely unbalanced, plants still grow well in the organic soil.
I hope this answered your question. Please write again if I can ever be of assistance.
