Question of the Week – Number 3: October 29, 2020

“Someone told me not to use pecan or oak leaves in my compost because they would harm the soil. Were they correct?”

I personally don’t think so. The theory is that tannic acid in their leaves will harm other plants’ growth. However, we live in a wooded rural area. Most of our trees are oaks and pecans, and I collect most of the fallen leaves with our mower and bagger. That process shreds them up into fine pieces so that they will decay more quickly in the compost pile.

My dad and I actually harvested pickup loads of humus from the floor of a post oak forest near our home in College Station when I was a teenager. My gardens always flourished.

Dad was a PhD botanist and range management specialist with a lot of soil science in his background, and he taught me that you can get too much of any type of organic matter in your garden soil. I learned that the hard way when I put fresh horse manure on a large vegetable garden. I re-learned it when I used fresh wood shavings out of a sawmill.

In both cases, the bacteria that went to work breaking down the organic matter also tied up the nitrogen that was in the soil. My plants were very pale green and extremely stunted, and adding nitrogen to the soil didn’t do anything to help them. I just had to wait for the decaying process to run its course. Then and only then the bacteria died. They released the nitrogen they had been hoarding and my plants grew luxuriantly, but they failed to produce flowers or fruit. Gardens in those two years were disasters.

We have lived in a pecan forest for the past 43 years, and I use all the fallen leaves in my compost (actually, just a low area out in our woods where we dump the shredded leaves and let them decay). In all of that time, I have never seen anything but improved plant growth by using the compost. The secret has always been in using the composted leaves after they have decayed to a point of being unrecognizable – generally 6-12 months. I combine it with equal amounts of shredded pine bark mulch, well-rotted manure and sphagnum peat moss. I also use 1 inch of expanded shale to help loosen my tight clay soil.