mulching a vegetable garden with 4-6 inches of wood chips

Asked March 8, 2016, 12:25 PM EST

For years (25+)I have heavily mulched my landscape beds around my home with locally available wood chips from tree cutters. My beds contain shrubs, many perennial plants and even tomatoes.I tend to mulch heavy and deep so as to avoid weeding.I do have trouble growing certain annuals like impatience,marigolds,even dhalias unless I push the chips way back or remove them in the immediate area (hard to do because of the four to six inch depth.) If the annual survives the first four or five weeks, it then seems to "start to adapt"to it's "new conditions" and will recover to one degree or another, but never reaching full potential due to the initial poor start. If I push the chips back and place a "plant collar" made from a plastic plant pot that plants are bought in, after cutting out the bottom, so that the plant is completely not able to touch the chips, many of the annuals that I grow will do much better. Without this effort the plants will either have holes eaten in the leaves, or turn light green and become sickly looking.(tomatoes do not seem to have any problems at all with holes or the light green leaves and the initial "stunting" of growth: however I place them into the same "permanent" plant collars that are left in the ground year round.) My thoughts are that 1) I may have macroscopic decomposers in the bark layers that are "on steroids" and 2) I have also recently read that I may be creating a temporary nitrogen shortage in the soil because of the microscopic decomposer's need of the soil nitrogen to be able to decompose the sudden mass dumping of organic matter. The effect therefore is holes made in the leaves by some larger decomposer organisms like leaf miners(?) and light green sickly plants that are trying to grow in a temporary nitrogen deficient environment??????? I originally started out with clay soil, but due to years of chipping and even burying my leaves under the chips, I now have a very rich humus layer that has intermixed with the clay. I do not use pesticides or fertilizer and believe that the years of mulching with chips has only been a positive addition to the soil. Last year I became involved in a local community organic garden. In the plot that I was in charge of I found heavy clay soil after "reclaiming the site" from a jungle of weeds. Being the lazy "chip addict" that I am,I went about the same method I described to you above. As you may have guessed,due to the garden being all annual vegetables nothing did real well and in fact the effect I described above was even more extreme. Not wanting to have to pull weeds (half kidding), but more importantly wanting to augment the soil with organic humus and add essential elements(N,P,K and trace minerals) naturally back to this garden, I want to know if there is a workable answer to my situation? The solution that I have come up with thus far is as follows: 1) send some soil samples in,so that I can get an actual analysis. 2) Instead of narrow rows and small "plant collars"; clear "wide rows" (eighteen to twenty four inches), so that the chips are further away from the plants and the soil. 3) Add four to six inches of composted soil to these "wide rows" creating a type of "raised bed" within and level with the chips. The composted soil hopefully will not be temporarily nitrogen deficient nor be overrun with macroscopic decomposers to eat the holes in the leaves. I am sorry for the long text; however I wanted to provide you with all the details. Can you please give your expert opinion? Thanking you in advance, I remain respectfully yours; W.F. from dbn.hgts.

Wayne County Michigan weed issues vegetables fruit and vegetables

1 Response

Several factors can affect the success of a garden. Soil pH, drainage, nutrient balance, microbes, soil temp, et al. Soil pH may inhibit the uptake of certain nutrients. Poor drainage can be an invitation to diseases. Nutrient deficiencies and excesses can affect plant health. The soil temperature can also affect the plants ability to thrive, The types and numbers of microbes in the soil can favor or deter the plants chance of survival. Heavy wood mulch can impact many of these. Wood chips may alter the soil pH and not all trees do the same thing. Soil moisture increases and soil temperature can be much cooler. Too much mulch and moisture could smother plant roots and create an environment inviting to diseases. Over time wood mulch can make the soil more fungal dominant which is fine for trees but may not so good for annuals and vegetable which prefer bacterial dominant soils. In clay soils it is important to make sure there is proper drainage since many plants do not like "wet feet". Other factors of wood mulch include Toxic Mulch. This is caused by anaerobic activity which can be detrimental to plants, although one would expect it to affect all the plants. Some woods actually have substances that restrict the growth of other plants (e.g. black walnut will inhibit tomatoes) so it is important to know what woods are in your mulch. Although wood chips are big "nitrogen robbers" more recent information suggests that the robbing is not usually significant as long as the chips are not incorporated into the soil.

Doing a soil test is highly recommended( MSU SOIL TEST ). This will give you a good place to start in determining the problem and finding a solution. . The holes in the leaves should be evaluated to determine the cause. Although likely an insect, some diseases and nutrient deficiencies can cause holes in leaves. Mulches can provide nice hiding spots and habitat for destructive insects. Removing the mulch layer around the plants is probably a good move as is creating a raised area, although studies have shown that a lighter layer of compost may be more beneficial. It is always important to keep the mulch away from the base of the plant. This can reduce the incidence of disease.

Here are some additional links:


Sour Wood Mulch

Soil Health

I hope this helps,