Evergreens in Compost Increases Acid Soil

Acid evergreens used in compost can change the pH levels of your garden soil, making it a high acid soil that will cause problems for your plants.
By Susan Glaese
March/April 1987
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Asparagus and most fruit trees prefer a pH between 6 and 7; I suspect yours is lower.

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I just read "Make Organic Compost for Your Garden" in which she said to "go light on evergreens" when building a compost pile. Now I'm antsy about my asparagus. 

When I moved to my present home in Maine last fall, I faced truly dreadful soil: an inch of slimy, acid red clay resting on bedrock, all on a 30 degree slope. To create growing beds, I used what I had most of, evergreen boughs, layer upon layer of mostly white spruce, alternating with lime and clay. Then I planted my healthy, seed-grown, compost-fed asparagus plants on these built-up beds and added a nitrogen fertilizer. I also planted seven fruit trees on the same mounds. 

My questions: Can I expect good results? Should I replant this spring, adjusting the soil composition? 

Evergreens in Compost Increases Acid Soil Levels

It sounds as if you have two major problems. The first is that your beds sit on bedrock, which prevents your plants from developing the deep root systems they need for optimum growth. Asparagus crowns are usually buried eight to 12 inches deep, and fruit trees are planted even deeper, depending on the root ball.

The second problem is the soil's pH. Heavy applications of spruce and fir would make your acid soil even more acid, drastically inhibiting the bacterial growth needed for decomposition and stunting germination in many plants as well. Asparagus and most fruit trees prefer a pH between 6 and 7; I suspect yours is lower.

I haven't seen the site, of course, but if I were you, I'd probably start over. First, try to find a garden site that's lacking in bedrock. Then incorporate as much well-aged compost as you can, made from a variety of less acid ingredients — straw, hay, manure, weeds, grass clippings. (Or you can buy ready-made compost.) Keep working this into the soil, and over the years you will see a difference in aeration, tilth, pH, and general health. Third, I've found that working sharp sand into clay soil makes a real difference. Finally, have your soil's pH checked, and then ask your local agricultural agent how much lime to apply for that reading.

I realize that all this sounds like an awful lot of work and goes against the ideal of using on-site materials, but it may be what it takes to cultivate plants that like neutral or alkaline soil. You might also want to consider raising acid-loving crops — such as grapes and most berries — which are better adapted to your area.

— Susan Glaese, head gardener 

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