Effect of Black Dyed Wood Mulch on Tomato Plants?

Asked June 16, 2015, 3:25 PM EDT

After more that 40 years of my growing tomatoes without mulch, my wife insisted on adding black dyed mulch around each tomato plant bought at a nursery. Initially the development of the leaves on the plants looked normal. Now the new leaves developing as the plants increase in size are curling up on the edges. The 2 varieties planted are Better Boy and Early Girl, blight resistant according to catalog information. We have had great success with these varieties in past years without the use of any mulch. My wife is a devotee of mulch. Can it be that the mulch is having an adverse effect on the plants? Does necessary repeated watering by rain or garden hose increasingly leach toxic chemicals into the soil to the point of killing of the plants? I do not know if the wood is from chemically treated shipping pallets because the mulch was applied by a landscaping company.

Montgomery County Pennsylvania

1 Response

Hi -

I would suggest removing the mulch around the base of the tomatoes especially since you do not know the source of the trees used to make the mulch. Tomatoes are very sensitive to jugalone, an allelopathic chemical that is found naturally in black walnut trees. The recent rain events could be leaching these compounds from the mulch into the soil if this is the case.

In the long-term, using wood chips or mulch in a garden even if you know the source of tree can change the soil pH and tie up nitrogen so you will need to compensate for that by adding from nitrogen in the form of fertilizer or compost.

Mulches can be very beneficial for the garden in terms of helping with weed control and maintaining soil moisture but I would suggest using a straw mulch or grass-clipping if you are not using some type of lawn care service or weed and feed type product.

Good luck.