Trees and turf roots

I have two mature cherry trees on my parking strip that are about 20 feet tall. Their roots protrude above the sidewalk level and are quite prominent. There used to be grass planted above them but it wasn’t well maintained and I took it out several years ago. After trying different plantings, I’d like to put sod back on the strip and wondered if it was best to cover the roots fully with soil and lay the sod on top of that, or if it would be okay to let the roots be partly exposed and lay the sod around them.

I am not sure that it would be wise to reinstall sod over your trees’ roots. You may want to mulch them lightly (no more than 2-3 inches, and keep away from the trunk), as described by a document formerly available from North Carolina State University Extension:
Excerpt:
“Exposed surface roots can become unsightly or in the way. Roots do not suddenly grow on the soil surface. Roots increase in diameter over a period of years. Soil erosion can speed their exposure. Exposed roots need protection from pedestrian and vehicle traffic including lawn mowers. Mulching exposed roots physically protects them as well as conserves soil moisture and prevents direct sunlight from heating the roots. Cutting off or covering roots with top soil are temporary solutions that can cause long term damage to tree roots.”

There is excellent, clear information in this link to the International Society of Arboriculture’s page on trees and turf. Ultimately, the best thing for your trees and your grass is to create a grass-free zone under the trees’ dripline, mulch that area, and restrict lawn grass to the area beyond the dripline. Here is an excerpt from the link:

“Trees, shrubs, ground covers, and lawn grasses all require sunlight, water, and rooting space for growth. Each plant in the landscape competes with neighboring plants regardless of type or species. Some even produce chemicals that are exuded from roots to restrict growth of nearby plants. For each plant to do well, it must have adequate space. Because perennial woody plants increase in size each year, they require additional space over time. The landscape design should provide adequate space for these plants to mature.

“While shade is the biggest, most obvious problem trees create for turf growth, a tree’s roots also contribute to poor turf performance. Contrary to general thinking, most tree roots are in the top 2 feet of soil. More important, the majority of fine, water absorbing roots are in the top 6 inches of soil. Grass roots ordinarily occupy a much greater percentage of the soil volume than tree roots and outcompete them for water and nutrients, especially around young trees. However, grass root density is often much lower in areas where trees were established first. In these situations, tree roots compete much better for water and nutrients and prevent or reduce the success of establishing new turf.

“Competition is especially important when transplanting, seeding, or sodding. The newest plant in the area must be given special treatment and must receive adequate water, nutrients, and sunlight, which frequently means that competing sod should be removed from around transplanted trees and shrubs or that some of the lower branches should be removed from existing trees above a newly sodded lawn. In any case, do not do any tilling around trees.

“Mulching is an alternative to turf around trees, and its use eliminates potential competition. A 2- to 4-inch layer of wood chips, bark, or other organic material over the soil under the drip line is recommended because it

helps retain soil moisture
helps reduce weeds and controls grass
increases soil fertility when mulch decomposes
improves appearance
protects the trunk from injuries caused by mowing equipment and trimmers that often result in serious tree damage or death
improves soil structure (better aeration, temperature, and moisture conditions)

“Maintenance practices for trees and turf are different. Because tree and grass roots exist together in the upper 6 to 8 inches of the topsoil, treatment of one may damage the other. Fertilizer applied to one plant will also be absorbed by the roots of a nearby plant. Normally that is good, but excessive fertilization of either trees or turf can result in tree crown or grass blade growth greater than desired.”

landscaping around septic systems

We have a new house that we have to landscape around. The biggest problem is that we have to be careful what we plan due to the septic system. It is an evaporation system, with two huge cement tanks buried under the ground in the front of the house and plastic pipes running through the side yard. We are planting grass in a rectangle right above the biggest bunch of the plastic pipes, but what can go around it or by the cement tanks that will not grow long roots and dig into it? In looking at the planting information on the packages and in my Western Garden Book, nothing seems to mention root depth.

Below is an article entitled What to Plant Over the Septic System by Mary Robson (originally published in her Regional Garden Column for Washington State University Extension, December 6, 1998):

“As more and more people move into rural areas, questions about septic systems and landscaping have become quite common. This column deals with some of the basics. A new brochure from Washington Sea Grant called: Landscaping your Septic System, offers considerable detail on the subject and provided much of this material.

“First, be sure that the septic field is clearly identified, and you know where the reserve area is. Keep all construction away from these areas. Understanding the functioning of the system is vital. Get information. (Some of it is available in video form.) The drainfield will not work well if overloaded with extra surface water, so be certain that it is not in the path of downspout run off or irrigation systems.

“Sunlight and air circulation also help the drainfield perform properly. Avoid surrounding it with tall trees. (Some shade is fine, but you would not plant an oak on the edge of a drainfield.) Set up some barriers so that it is not compacted by frequent foot traffic. Occasional mowing or moving through the field to check the system is certainly fine, but you do not want the drainfield in the middle of a heavily used path.

“There are advantages to using plants over the drainfield. Plants do help provide oxygen exchange and contribute to evaporation necessary in the drainfield area. Choose plants with shallow, non-invasive roots. You do not want breakage or damage in pipes from root intrusions.

“Grasses are most commonly recommended for the septic area. Lawn can be attractive. Do not overload the system by watering it a lot. Meadow grasses or a mixture of turf grasses like perennial rye and some broadleaf flowers (such as yarrow) can also look good and require little maintenance. Several mixes sold as Eco-Turf or Fleur de Lawn have these components.

“Small, shallow-rooted ornamental grasses (for instance, Festuca ovina
\’Glauca\’ 4-10 inches) can also be good looking. Very tall grasses like Stipa gigantea are not appropriate. Avoid over-active plants like English ivy (Hedera helix), which is becoming a menace in forested areas by moving in and stifling trees.

“Edible crops are not suggested. Vegetable gardening requires frequent cultivation, and digging in the drainfield area is inadvisable. Also, the brochure notes that: Sewage effluent is distributed through the soil in the drainfield area. Any root vegetables planted in this area may be directly exposed to septic tank effluent.

“Other possibilities are low-growing ground covers. Some, such as bugle weed (Ajuga reptans) and vinca (Vinca minor) grow vigorously and would fill in quickly. The native kinnikinnick (Arctostaphylos uva-ursi) grows well in full sun but is slow to establish. A mulch around the plants may help with weed control while the plants spread.

“The green growing layer over the septic tank helps the system to function, adds to the appearance of the landscape, and should, ideally, be set up to allow easy monitoring and maintenance. Keep landscaping simple and straightforward, remembering that the object is the good performance of the system.”

To get more information on septic systems, contact your local health department. The brochure Landscaping Your Septic System (pdf) is available through the Sea Grant Program.

Here are links to publications that might also be helpful:

Mounds: A Septic System Alternative

Understanding and Caring for Your Sand Filter System

Care and Feeding of Septic Tanks

on adding sand and manure to clay soil

We would like to put in a new lawn around a home where there were mostly weeds. The soil is very a heavy silt because it is river bottom land. I have access to free sand; however, I’ve heard conflicting advice regarding adding sand to clay — some say yes, others no. I also have access to a large supply of free horse shavings/manure from a horse stable. Would those shavings be good to add to the soil to help lighten it and add nutrients? I don’t want to go to the expense of bringing in topsoil if I don’t have to. What are your suggestions?

Adding sand to clay soil is not recommended as a way of lightening the soil, as it “may create a concrete-like structure”, according to the booklet Ecologically Sound Lawn Care for the Pacific Northwest by David K.
McDonald. Linda Chalker-Scott addresses the reasons for this in depth in “The Myth of Soil Amendments Part II”.

Instead of adding sand, David McDonald recommends trying to till in compost. At least two inches of compost tilled into the upper six to eight inches of soil is recommended, but four inches tilled into the upper twelve inches is preferable . Try to avoid doing this when the soil is waterlogged, as it may damage the soil structure.

Composting the horse manure and shavings you have access to could be a feasible way to obtain the compost to till into the soil. The Guide to Composting Horse Manure by Jessica Paige of Whatcom County WSU Extension discusses how to compost and use horse manure. She recommends curing such compost at least a few weeks before application, and adds that one to three months is a good, typical composting time in summer or three to six months in winter.

Alternatively, according to David McDonald, if there are a few months of warm weather between autumn and seeding time, you could simply till the fall leaves and grass clippings into your soil. Depending on your planned schedule, this could be very easy. (You can find McDonald’s full booklet “Ecologically Sound Lawn Care for the
Pacific Northwest: Findings from the Scientific Literature and Recommendations from Turf Professionals” online as a very large PDF.)

Another option might be to consider some sort of groundcover if you discoverthat establishing a lawn is an excessively extensive project. Carex species or possibly Juncus phaeocephalus phaeocephalus are more naturally adapted to heavy soils in wet areas than lawn grasses and so may be less work in the end. Though they would not be appropriate for a heavy traffic area, they would be grasslike in structure. Sagina subulata might be more amenable to heavy traffic.

selecting lawn grasses for the PNW

I’m looking for a type of lawn grass that is fairly drought-tolerant and will do well in our area (Seattle). Any suggestions?

One of the best resources for local information about lawn seed selection and general maintenance is David McDonald’s Ecologically Sound Lawn Care for the Pacific Northwest. It is available in print form as well as online from the City of Seattle. In it, he recommends a mix of turf-type perennial ryegrasses and fine fescues (such as chewings, creeping red, and hard fescue) for their flexibility in a range of local garden conditions. Ryegrasses thrive in full sun, and fescues take sun but will tolerate some shade. He also suggests ecolawns (sometimes called ecoturf) which mix grasses, clovers, yarrow, daisies, and other small flowering plants, because they tolerate dry sites, do not need fertilizer, and generally require only monthly watering. They also need mowing less frequently.

grass seed selection and planting for PNW gardens

I want to put in a wee bit of lawn, an area of 240 square feet. I have two questions: 1) what seed would you recommend for an area that is mostly dappled shade? 2) how do I prepare the area correctly?

on growing buffalo grass in the PNW

I was interested in trying out buffalo grass (Buchloe dactyloides) ‘Legacy’ from High Country Gardens. I was wondering if you knew anyone who has tried growing it in the PNW (esp. Whidbey Island) and what they thought of its performance.

According to the Sunset Western Garden Book, buffalo grass is best suited to Sunset zones 1-3, 10, and 11. Whidbey Island is Sunset zone 5. While the Sunset book does not address ‘Legacy’ in particular, you may find that this grass is not the best choice for your location.

The Washington State Extension in Puyallup created a ranked list of good turf cultivars for Western Washington.

Additional information, from the Extension, about lawns. Note that there is an article about buffalo grass, but it is focused on whether that grass will do well in Central Washington, not Western Washington.

Sustainable lawn care

I am looking for general information on lawn care, lawn renovation, lawn fertilizer and alternatives to pesticides.

Here is information from the web pages of Seattle Public Utilities. An excerpt:

Fertilize Moderately:
Use “Natural Organic” or “Slow-release” fertilizer. These fertilizers release nutrients to feed the lawn slowly, and less is wasted through leaching or runoff into our streams. Look for the words “natural organic” or “slow-release” on the bag.

Fertilize in September and May:
With slow-release or organic fertilizers, you can fertilize just twice a year, in mid to late May and again in early September. If you choose to fertilize only once, the fall application is most important because it helps the grass grow new roots and store nutrients for next year’s growth.

How much to apply:
Washington State University (WSU) recommends that home lawns receive 3 to 4 pounds of nitrogen (in a balanced fertilizer) per 1000 square feet of lawn each year. Grasscycling can supply at least one-quarter of that. Split the rest between the May and September applications. Avoid fertilizing in the early spring because it makes lawns grow too fast (unless your lawn needs help recovering from disease or insect damage.) Wait until May.

Mow better:
Grasscycling returns valuable nutrients to the soil every time you mow! Mow high, mow often and leave the clippings to see results.

Fertilize for a healthy colored lawn”
Healthy lawns are a medium green color (top), depending on the variety of grass. The darkest green turf (bottom), which many people strive for, is not in fact the healthiest turf. Overfertilized lawns are more prone to disease, thatch buildup, and drought damage.

Test for calcium deficiency:
Soils west of the Cascades are often low in calcium. Apply lime in the spring or fall if a soil test shows a calcium deficiency or acid soil conditions (pH less than 5). Call WSU Cooperative Extension (206) 296-3900 for information on soil testing and their Home Lawns bulletin.”

If you would like to renovate your lawn, this is something you could do in the fall. Local garden writer Ann Lovejoy describes her method in The Handbook of Northwest Gardening (Sasquatch Books, 2003):

Mow the existing grass as short as possible.
Spread 1 inch of clean crushed quarter-ten gravel (not pea gravel) evenly over the entire surface.
Spread 1 inch of compost over the gravel.
Top-seed with a regionally appropriate blend if the lawn is thin and spotty.
Wait 6-7 weeks before mowing again.

Should you decide to start afresh, here is information from the Washington State University Extension website which discusses grass seed for Western Washington gardens. Here is an excerpt:

What Grass Seed Grows Well in Western Washington?
“To establish a lawn in western Washington, choose a combination of turftype tall fescue grasses and turftype perennial rye grasses. A mix that adds up to about 90% of these two grass seed types will grow well in either sun or light shade in western Washington. Turftype perennial ryegrass takes full sun and stands up to traffic. Turftype tall fescues are adapted to shadier locations. In combination, the mix works for a lawn in average light conditions. Mixes containing fine-leaved fescues or chewings fescues will also establish well. Fine-leaved fescues offer bright green color, and will take some shade, but do not take heavy use.

“Many commonly-grown grass types from other areas of the United States will not thrive in western Washington’s cool, dry summer climate. AVOID mixes with high concentrations of Kentucky blue grasses. DO NOT PLANT Zoysia, bermuda, dichondra, centipede, carpetgrass, St. Augustine, or mondograss. Buffalograss isn’t suitable for western Washington, though it may thrive in eastern Washington.

Soil Conditions for Planting a New Lawn:
“Establishing a new lawn successfully depends more on the preparation of the ground before planting than on whether the lawn choice is seed or sod. Lawn failures are often caused by poor soil conditions under the roots. Many times soil surface left for planting after new construction is infertile subsoils, with rocks, lumps, and building detritus left in it. The texture may vary from sands and gravels to heavy, poorly drained clay areas. The best soil texture for a lawn is a sandy loam, containing 60%-70% sand and 30%-40% combined silt and clay.”

If the soil isn’t well-drained, do not try to amend a heavy clay by dumping sand into it. Adding sand doesn’t work, nor does adding gypsum. Amend the soil with organic material, which will help in creating better structure. Use compost, manure, aged sawdust, ground bark, or other organic (previously living) materials. Spread 2 inches on top of the ground and work it in thoroughly 6 to 8 inches down. Getting it completely incorporated is important, because spots of organic material in clumps may decompose and cause a low spot in the finished lawn. Rake away clods and remove large rocks and litter.

University of Minnesota Extension’s Caring for Shoreland Lawns and Gardens describes best practices for caring for a shoreline lawn and garden, which includes using compost as lawn fertilizer. An excerpt:

If possible avoid the use of chemical fertilizers. Native vegetation does not require the application of additional fertilizer. Use caution if applying fertilizers to lawns and adhere to the following guidelines:
Have your soil tested to determine how much fertilizer is needed and minimize the use of chemical fertilizers; soil test sample bags are available through the county offices of the University of Minnesota Extension Service.
Use compost or manure; this is preferable to chemical fertilizer. However, these also have the potential to damage water quality if used in excessive amounts.
If chemical fertilizers are used, select slow-release (water insoluble) forms; see recommendations for fertilizing on next page.
Water your lawn after fertilizing, but do not allow excess water to run off into surface waters.
Sweep up any fertilizer spilled on hard surfaces such as walks and driveways, instead of washing it off.
Use extra caution when applying fertilizer near surface waters; do not spread fertilizer within 75 feet of surface waters or wetlands; use a “drop” spreader and not a “cyclone” spreader to minimize the possibility of getting fertilizer directly into the water.
Never apply fertilizers to frozen ground.
Leave a natural vegetation filter strip of grass, trees, and/or shrubs next to the shoreline; another option would be to construct a berm along the shore.

You may find this general information about compost, from the City of Seattle Public Utilities and the Saving Water Partnership, of interest.

Here are additional links to lawn care methods. The first three are from the Northwest Coalition for Alternatives to Pesticides:

Taking Care of Your Lawn without Using Pesticides.

Dealing with Dandelions.

Pesticide-Free Techniques for Dealing with a Mossy Lawn.

From Toxic-Free Future (formerly Washington Toxics Coalition):
Choosing Fertilizers for the Lawn & Garden.

From Beyond Pesticides:
Read your “Weeds”–A simple Guide to Creating a Healthy Lawn.

removing fairy rings in lawns

I’ve researched “fairy ring in the grass” online, but haven’t come up with any surefire solutions. Ours is about 3 feet across, with scant grass in the center. Digging it out and replacing grass or hiring a professional to apply toxic fumigants seemed logical. Any other suggestions to try?

I think physical removal is certainly a better option than applying toxic fumigants, though it requires some work. Washington State University Extension offers these recommendations for fairy ring in lawns:

Several species of fungi can cause fairy rings in lawns. The common symptoms may include a ring of dead grass with darker green grass and mushrooms on the inside and/or the outside of the ring, circular patches of darker green grass, or rings of mushrooms or puffballs appearing with or without other symptoms. Mushroom rings most commonly appear in the spring or fall when adequate moisture is present. The type of fairy ring which causes dead rings is the most damaging. The fungus feeds on decomposing organic matter such as dead tree roots and undecomposed bark mulch in the soil and makes water penetration difficult. Fairy rings are more severe on sandy soil with low fertility. Grass inside the rings may be weakened or killed and replaced with weeds and weedy grasses. Fairy rings may disappear suddenly.

Select Non-chemical Management Options as Your First Choice!!

After rewetting, reseed affected areas and fertilize and water properly.
Provide proper culture, including deep, infrequent waterings and adequate fertilization.
Rake and loosen soil in affected areas. Aerate soil and water the area deeply. A grass-type wetting agent can be used to help rewet the soil.
Remove the sod, mix soil in affected areas in the upper 6 to 8 inches of soil with a rototiller, and reseed or put new sod in the area.

Pesticides: None recommended (Revision Date:4/20/2010)

In his book, The Chemical-Free Lawn (Rodale Press, 1989), Warren Schultz says of fairy rings:
“The only sure way to eradicate the mushroom is to dig out the turf and soil to a depth of 2 feet, extending outward at least 1 foot beyond the edge of the circle. It’s also possible to slow the fungus by drenching the soil with water to a depth of 2 feet. Some turf experts recommend fertilizing the rest of the lawn heavily to mask the green color of the ring. This practice, however, may encourage other diseases [my note: heavy fertilization contributes to toxic stormwater runoff]. You may be best off learning to live with the disease.”

This information from Oregon State University (no longer available online) provides advice on removing fairy rings from lawns:

Soak Fairy Ring area daily for a month with water. Punching a number of holes in the area to be soaked will help get the water into the soil. The Fairy Ring area is often dry, hard and difficult to get water into the soil. A thorough aeration in April with a rented machine will make the job easier.
Adequate fertilizer will mask the green ring by supplying the entire lawn with extra nitrogen.
Renovation of affected area can be accomplished by removing the affected sod and soil. Cut the area 12 inches wider than the outside of the ring. Cut the sod and soil 1-2 inches deep. Remove affected material. Replace with ‘clean’ soil and replant.

managing mushrooms in lawns

Our backyard (which is flat and no pine trees) has hundreds of tiny mushrooms throughout the grass. Our front yard (which has a slight slope and one large pine tree) has many huge mushrooms. Otherwise, we have good looking grass. We have lived here for a very long time without ever seeing this problem. I know one answer is to “sweeten” the soil with lime. Should we do this now, in the fall, or at what time of year? Should we remove the mushrooms or let them be? Any other suggestions?

University of California, Davis Integrated Pest Management has guidelines on managing mushrooms in lawns. Here is an excerpt:
“Mushrooms found in lawns often develop from buried scraps of construction lumber, dead tree roots, or other organic matter. The fungi that produce these mushrooms are beneficial because they decompose organic matter in the soil, making nutrients available to other plants. These mushrooms usually are harmless to grasses, but some people consider them unsightly or want to get rid of them because young children play in the area. Remove mushrooms growing from buried wood or roots by picking them as they appear or by digging out the wood. Many of these mushrooms are associated with overirrigation or poor drainage. Removing excess thatch and aerating the soil to improve water penetration may help in some cases.”
The website further suggests adding nitrogen fertilizer, but bear in mind that excessive fertilizer contributes to urban runoff pollution.

As for sweetening the soil with lime(making it less acidic), it is best to do a soil test before attempting to amend for soil pH. The City of Seattle’s Natural Lawn Care information says that you would only need to “apply lime in the spring or fall if a soil test shows a calcium deficiency or acid soil conditions (pH less than 5).”