Garden Detective

Garden Detective: Dead lawn has him focused on topsoil

Q: We live in Roseville close to Rocklin, and our soil (if you can call it that) is composed of what Rocklin is named for, i.e. rocks. When the sod for our front lawn was placed, it was rolled right onto the rocky soil; no topsoil, nothing.

As a result, because the roots are very short, as short as the sod is deep, our lawn is not very drought resistant at all. In fact, it requires twice-daily waterings during the summer or the sod dries out in the humidity and heat of the Sacramento Valley summer.

Much of our lawn has died as a result of this drought.

If and when this drought finally ends and we’re allowed to water our lawns again, I’m considering tearing out our current lawn (most of it is dead anyway) and putting in new sod, but I’d like to get some decent topsoil under the sod. How deep should that topsoil be? I’m thinking at least a foot if not more. The deeper the roots, the better the drought resistance. (A so-called native-plant front yard is kind of out of the question, as such a yard would not fit in with the neighborhood at all.)

William Oertell , Roseville

A: According to UC master gardener Rachel Tooker, you may still want to consider an alternative to traditional turf.

California has continued into another year of drought and the governor has implemented mandatory water use restrictions that are changing how many communities use water.

In Roseville, residents are being asked to reduce their water use by 28 percent compared to 2013 totals. In addition, the city of Roseville has enacted watering day restrictions (a maximum of two days per week).

You may find that the aesthetics are changing in your neighborhood and more homeowners will be switching to a water-efficient landscape, especially for under-used or little-used turf areas. Because in this region landscape watering (particularly for turf) accounts for up to 60 percent of homeowner water use, there are also compelling reasons to reduce the total amount of turf in your yard.

You appear to have an accurate diagnosis regarding why your current lawn has not thrived, especially in drought conditions. Lawns with strong roots have the best chance at fighting insect and disease problems, retaining moisture and also avoiding weed invasions.

Also, lawns that are mowed at no less than 2 to 3 inches in height (for tall fescue) will encourage a deeper root systems and more water retention.

Ideally, topsoil should be a minimum of 6 to 8 inches in order for grass to develop a good root structure. If you choose to add topsoil, make sure to mix it into the existing soil in order to avoid stratifying old and new soil. New soil spread on top of the old soil without mixing creates a layered profile, making it difficult for water or plant roots to penetrate the bands of different soil.

When adding soil, be sure to add a loamy type of soil that is free of rocks, herbicide residue, weed seeds, propagules such as rhizomes of bermudagrass or nutlets of nutsedge, or other debris.

Depending on the topsoil mixture used, you may also want to add some organic material (compost) to improve the soil structure. Use a rotary tiller to incorporate the organic material and mix it thoroughly with the new and existing soils. For instance, a layer of 1 to 2 inches spread over your site should be tilled to a depth of 3 to 6 inches.

Another important consideration as you add new soil is grading and paying attention to where water will flow once the lawn is established. Avoid planting lawns on steep slopes or berms to reduce water waste from runoff. Slope soil away from buildings and allow the lawn area to settle for one to two weeks before sodding. Generally, a 1- to 2-percent slope away from buildings is sufficient.

In addition, allowing time for several wetting and drying cycles before you add sod or seed will aid soil settling and help locate low spots that need filling.

There are many resources to help you establish a beautiful landscape that is also more drought tolerant. The city of Roseville includes several water-efficiency pages on its website and also offers free “Water-Wise House Calls.” A review of the publication “Rules of Thumb for Water-wise Gardening” (available on the city’s website) may help you to make choices where and how you re-establish your lawn once the drought is over.

For more information, consult the master gardener website at ucanr.edu/sacmg and, on the UC IPM website, “The UC Guide to Healthy Lawns.” Also check out the city of Roseville’s Water Efficiency page.

For more ideas on water-wise alternatives to turf, check out the planting guides at www.BewaterSmart.info.

Garden questions?

Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties. Send questions to Garden Detective, P.O. Box 15779, Sacramento, CA 95852. Send email to h&g@sacbee.com. Please put “Garden Detective” in the subject field and include your postal address. To contact UC Extension directly, call:

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