A study in Marigolds and Mulch

VegHeadz gardeners have planted marigolds in various ways following information about their ability to repel nematodes and to attract pollinators to the garden. 

After temperatures in the low 30s over the last week, when we worked in the garden today we noticed a striking difference in how two beds of marigolds reacted to the cold. In a raised bed planted by MG Jeanne Breland, a marigold cover crop was bitten back quite severely by the cold. Planted there was a variety sold as “French marigolds,”   probably  “tagetes patula.”   

Cold-damaged
French Marigolds

About 20 feet away and at a slightly lower elevation three varieties including “tagetes patula” planted by MG Kwan Park to attract pollinators showed no signs of damage from the cold. 

So what was the difference? The marigolds in the raised bed which were damaged had been mulched two weeks ago with dry tree leaves. The light brown leaves had not yet begun to decompose to any extent.

Undamaged Marigolds

Marigolds in the lower bed were mulched last week with a layer of partially composted fine mulch from the Leon County’s solid waste facility. This dark mulch had been sitting in a pile in our garden area for some time and had begun to decompose. Our theory is that the sun heat absorbed by the dark color of the mulch and the heat from the composting process made enough difference in the ambient temperature in that area to protect those marigolds from the cold.

The takeaway is that a compost mulch in fall will not only provide nutrients for your spring crops and discourage winter weeds, it may provide some cold protection to nearby plants.  Sometimes a small bump in temperature means the difference in winter survival.

For the bottom line on marigolds and nematodes, see the IFAS article below.  https://edis.ifas.ufl.edu/pdf/NG/NG04500.pdf

Among other things, this article points out that the best way to utilize marigolds for control of nematodes is to plant them thickly as a cover crop as Jeanne did at least two months before the next vegetable crop and in the exact place where the next crop will be planted.   The marigolds do not repel nematodes, they actually attract them.  The marigolds act as a trap crop when the nematodes invade their roots, cannot develop further, and die because of a chemical secreted by the marigolds.  This benefit lasts only one season.

Marigolds planted to attract pollinators can be planted anywhere throughout your garden   

There’s much more to learn, so check out the article.