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Wednesday - May 04, 2011

From: Charleston, MO
Region: Midwest
Topic: Compost and Mulch, Soils, Trees
Title: Will wood shavings in the soil require nitrogen from Charleston MO
Answered by: Barbara Medford

QUESTION:

I cut down a big maple tree and a lot of the wood shavings was left in the soil. I planted a flower bed over the area this spring. I later read that the wood chips in the soil would use a lot of nitrogen. What can I use to replace nitrogen that is used up. I used a slow release fertilizer when I planted my flowers and worm castings, but feel I will need to add extra nitrogen soon. I planted blanket flowers, carnation, queen salvia, and aster. I don't want to burn my plants by adding the wrong thing. How often will I need to add extra nitrogen? Anything you can tell me will help. I live in zone 6b.

ANSWER:

This particular member of the Smarty Plants Team has personal experience with that sort of situation. In our case, it was a Liquidambar styraciflua (Sweetgum), which has a palmate leaf, Fall color and invasive roots, like a maple. In our case, those roots were pushing up the driveway and sidewalk and trying to get into our house via the foundation, and we had it cut down and the roots ground, which left a great deal of chopped root in the flower bed we created where the tree had been. After the tree was cut down, there was a period of a month or so while the new driveway and sidewalk were poured, and a bed for plants with not-so-invasive roots was created. After that, we planted roses and irises in the bed, and they flourished extremely well. In fact, one gardener for whom we dug up some iris corms asked wistfully where we had gotten that great dirt.

We had also read that putting a shredded wood mulch on plants could cause some nitrogen deficiency, and now recommend that either some nitrogen fertilizer be added to the soil, or that the mulch material be composted for a period of time. In our case, the wood scraps were thoroughly mixed into the soil by the root grinding operation, and perhaps decomposed sufficiently in the period before plants went in to avoid the problem.

Rather than just add nitrogen, we would recommend that you wait and watch for symptoms of nitrogen deficiency. We found this article on Nitrogen Deficiency in Plants from the University of Arizona Cooperative Extension. Granted, they are dealing with desert soils unlike the soils in Missouri, but the discussion of symptoms was so explanatory that we thought you should read it. We also found this eHow article on What Type of Soil is in Missouri? Since the pH of your soil can have an effect on the availability of subtances such as nitrogen in your soil, you might consider getting a soil sample from your property. You can contact the University of Missouri Extension Office for Johnson County, which not only can provide you with instructions for soil testing, but probably knows what kind of soil you have in your area.

Bottom line: If it ain't broke, don't fix it. Too much nitrogen in soil will cause lots of green leaves (it's the major ingredient in lawn fertilizers, for instance) and defer or limit blooming. Those wood chips will probably decompose without seriously affecting your plants; just keep an eye on the plants as they develop. If you feel you are seeing deficiency, that is the time to add some liquid fertilizer with a relatively high nitrogen content, but don't get carried away. You are correct in hesitating to burn your plants with an overdose of nitrogen.

 

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