Garden Detective: Which mulch is best, bark or compost?

05/03/2014 12:00 AM

05/01/2014 5:15 PM

I read with interest your article on birch trees in Sacramento; lots of great help there. But I think you’re mistaken in saying that bark chips should be put around the trunk of the tree. When I got a free shade tree from SMUD, I was told to use compost around the tree, not bark chips. In fact, the SMUD tree person told me that the bark chips around my citrus trees were part of the trees’ problem. Bark is not made to decompose so it doesn’t help the soil. Also earthworms won’t live in there. I called Sacramento County extension and they corroborated, so I removed all the bark chips and replaced with compost. The trees are happier and I do have lots of earthworms now. Please let me know your thoughts.

– Lois Van Beers, Sacramento

Organic mulch – such as shredded bark or wood chips – has benefits, according to UC master gardener Carol Hunter. Bark and wood chips break down more slowly than compost. On the other hand, the nutrients in the compost are more readily available to the tree or shrubs because the organic matter is already partially broken down.

When a new tree is planted, an area of about 4 by 4 feet should be cleared of grass. Mulch is applied on top of the soil. Mulch moderates soil temperature and slowly decomposes and enriches the soil. It also helps retain moisture.

The use of bark is beneficial to reduce the growth of weeds since it keeps light from reaching the soil. Whether to use just compost or bark mulch is dependent on the owner’s preferences. Whatever is used, it should be kept about 4 inches away from the trunk of the tree to avoid crown rot.

The Sacramento Tree Foundation and SMUD’s Shade Tree Program as well as University of California all recommend the application of mulch. We are mystified by the information you received.

Our lawn is being overrun by some type of weed grass. Many of the neighbors have it growing in their lawns as well. What is it, and what steps can be taken to control it?

– Randy Geisick, Elk Grove

According to UC master gardeners Carol Hunter and Mary Griggs, the weed pictured in the photo provided appears to be dallisgrass, occasionally confused with crabgrass.

A major component of dallisgrass management is preventing establishment of new plants. In home landscapes, removing young plants by digging them out before they form rhizomes or set seed is the best strategy for control. Mature plants can also be dug out, but they sometimes grow back if rhizomes are left behind. When dallisgrass is abundant or the plants are located over a large area, it may be necessary to supplement cultural practices with herbicides.

Weed-Hoe or Weed-B-Gon Crabgrass Killer for Lawns can be used by home gardeners to control clumps of dallisgrass growing in lawns. These herbicides are relatively selective and must be applied two to three times at three-week intervals in the summer. Also, it is best if the turf is left unmowed for two weeks before the first application. Withhold irrigation for 24 hours after application. Don’t apply these herbicides during extremely hot weather and check the label for rate adjustments during warm weather to minimize the risk of injury to the turfgrass.

Preemergent herbicides can be used in established turfgrass to control germinating dallisgrass seed. Apply preemergent herbicides in late winter or early spring before dallisgrass seed germinates.

Additional information regarding dallilsgrass is available online at www.ipm.ucdavis.edu.

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