Be aware of mulch residue

Garfield County Master Gardeners

As everyone who tries to raise tomatoes knows, doing the same thing every year doesn’t guarantee the same results.

My husband is the tomato raiser at our house and has had quite remarkable crops for the past three or four years.

Although he has continued to amend the soil in his slightly raised beds, experimented with different cages, and tried several varieties of tomatoes, one thing he has consistently done is generously mulch the tomato beds with wheat straw.

With the usual high hopes and great expectations that accompany the launch of every gardening season, my husband planted two beds of six Early Girl plants we had purchased at a local nursery.

Although a few late cold nights delayed the planting, the young plants quickly doubled in size and looked great.

A couple of weeks later, we had two unusual episodes of strong northeast winds, which battered the little plants. In spite of tattered leaves and some broken branches, the plants seemed to be thriving. Some already had little tomatoes.

With hot, windy, dry weather on the way, the time had come to mulch the tomato plants. The straw we use for mulching comes from bales we leave in the weather so they will get dark and begin to decompose.

Just as he has done for years, my husband broke open a couple of those bales and mulched the tomato beds. With that chore completed, the plants will enjoy cooler, damper soil through the hot summer. We’re good to go.

But, within a couple of days, one of the plants withered dramatically. The rest of the plants had grown taller, but looked pale with new growth curling weirdly. My husband suggested the battering from the strong north wind had injured them more than we had realized.

I thought the plants looked as if they had been exposed to chemical drift, but we had not sprayed anything nor had our neighbors. I was on the right track but was way too slow in figuring it out.

Finally it came to me. The straw that we used for mulch was not from the same source as what we have used in the past. We had no way of knowing, but this straw might have been sprayed with a broad-leaf herbicide. Tomato plants are notoriously sensitive to chemical exposure, so even a very small amount of residue in the straw could be problematic.

My husband immediately removed the straw from the tomato beds and replaced it with bagged Western Red Cedar mulch. Although we don’t know if

the plants will recover, we do see hopeful signs such as much improved color in the leaves, more normal-looking new growth, and healthy-looking blossoms. We may yet have some tomatoes.

At a master gardener meeting some months ago, we discussed the hazard of chemical residue in mulch. I should have recognized the problem right away.

I hope my story raises awareness of chemically contaminated mulch. You have to know your straw.

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Vculek is a member of Garfield County Master Gardeners.

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