Issue: March 10, 2001

Grass clippings and lawn thatch


I'm confused about thatch removal. I thought you should leave grass clippings on as mulch. Doesn't that increase the thatch? Linn Las Cruces


Thatch is the accumulation of dead stems and roots of grass, not the leaves. The leaves tend to decompose rapidly, so grass clippings left on the lawn do not contribute directly to thatch buildup. Leaving the grass clippings on the lawn is beneficial if you manage them properly.

Proper management involves mowing frequently so that the clippings are small enough that they can filter through the grass, not accumulating on the surface shading the uncut grass blades. Another important consideration is that nitrogen fertilization be reduced by one-third when grass clippings are left on the lawn. These clippings decompose, returning some nitrogen to the lawn. Without reducing the nitrogen supplied, increased root and stem growth will indirectly result from the grass clippings. In that case, the clippings can contribute indirectly to thatch buildup.

Remember that up to one-half inch of thatch is beneficial in cushioning the grass crowns from traffic, but thatch over one-half inch in thickness can cause irrigation and disease problems. Once the thatch exceeds one-half inch it should be removed by power raking, or manual raking just as growth begins. De-thatch cool season grass early in the spring and early in the fall, warm season grass in the early summer. It is important to de-thatch when the grass is actively growing so that it can recover from the injury caused by the intense raking.

Carpenter bees and roses


I was out pruning my roses today, March 1, and noticed that a couple of my rose bushes seem to have what looks like borer damage. Several canes were completely hollow through the middle, and you could see the sawdust-type particles in many of the other canes. Is this borer damage? If so, what is my best defense to rid the roses of them? Should I just take the rose bushes out to risk infecting others? I watch your show on Saturdays and really enjoy all the local information. Sheila Salsman Corrales, N.M.


You are describing carpenter bees which will burrow into the pith of rose canes to lay their eggs. These bees aren't particularly bad, except when they damage our rose stems. Otherwise, they are pollinators doing good. They are solitary bees. They don't form large hives where you might get stung, so they are not a major worry from that perspective.

The solution is to deny them entry into our roses to prevent damage but not to kill the bees. Coat the cut ends of the rose stems with white glue. This will seal the ends, preventing damage by the bees. They will find more hospitable locations to raise their families, usually not places that damage our gardens.

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Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email:, office: 505-865-7340, ext. 113.


For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

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