Question from Harry: I have heavy clay soil. When it gets wet, it sticks to my shoes. Recently I got a load of chipper materials from a local tree-pruner. I have been wheelbarrowing it around and spreading it on paths and beds and around my fruit trees. Would it be okay to dig it into the ground to lighten the soil in my vegetable garden before planting planting vegetables?
Answer from Pat: No. Do not dig chipper materials into the ground until they are fully rotted, which usually takes a year or two and often even longer. Chipper materials from tree trimmers make excellent organic mulch for covering bare garden soil, but all raw woody materials, such as sawdust, wood chips, or shredded wood, will rob nitrogen from the soil in order to rot. If you dig chipper materials into the soil of your vegetable garden it could kill your vegetables or at least give them yellow leaves.
Here is a list of organic substances that you can safely dig directly into garden soil:
- commercial organic soil amendment intended as planting mix
- bean straw
- apple or grape pomace
- homemade well-rotted compost
- fully composted wood shavings
- grass clippings
- green manure
- ground carrot, apple and vegetable fibers
- kelp and seaweed,
- leafmold
- aged horse or cow manure
- rabbit manure
- rotted hay
- sludge
- wet and sloppy vegetable and fruit leavings from your kitchen or supermarket
After chipper materials have been lying on top of the ground as mulch for a year or two, during which they have been frequently moistened by rain or sprinklers, most of the woody product will have absorbed enough nitrogen from the air in order to rot and will thus become like compost and can be incorporated into garden soil. This is the time to add more fresh mulch on top. Even after a year or two you may find that some big chips of wood or leaves have not composted enough to be combined with soil. Rake these bits aside and let them sit longer with your next load of mulch until they too have fallen apart and become indistinguishable from soil. Then you can safely dig them into garden soil to build its humus content.
For more on this subject, please see page 22 in my new organic gardening book, lower left hand column. Please also see the chart on pages 28 to 30 for an extensive list of organic soil amendments and an explanation of how to use each one. This chart will tell you which substances you can mix into soil and which should not be mixed into soil without adding nitrogen. It also tells you how much nitrogen to use.
Another chart on generic fertilizers was accidentally omitted from this printing but will be included in the next printing. (See this website under Fertilizers for that chart.) I suggest you download it, print it, and stick it in the back of your book. And thanks for writing me to ask such a good question.
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