Turf Culture in Shade

Tom CookOregon State University

2008

Some thoughts on shade:

This series of slides shows the types of problems associated with shaded lawns and offers general advice on growing the best lawn possible in shade. Normally, when I troubleshoot shady lawns, I see extreme cases where people want to grow grass in places where it simply should not be growing. One of my most common recommendations is to redesign the areaand replace the lawn with some other landscape treatment that has a reasonable chance to succeed. You should never have to make Herculean efforts just to have a lawn.

I don’t actually see shade as a major problem in growing nice lawns as long as it is not toodense for too many hours of the day. In fact if the landscape is properly designed and your irrigation system is properly zoned, partial shade can be the easiest place in your landscape to maintain. My idea of a good shady lawn environment for cool season grasses in the Pacific Northwest is a lawn that receives full sun in the morning and significant shade all afternoon. That creates an environment where there is enough sun to grow healthy grass, the dew dries out in the morning, and the shade moderates the heat load during the afternoon. Afternoon shade helps reduce the water requirements of the grass and makes it easier to irrigate effectively. It also creates a nice place to sit in the heat of the day!

MorningShade

Tree root competition

AfternoonShade

Shade poses many challenges

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Morning shade and tree root competition are two of the worst scenarios for shady lawns. The only thing that is worse is full shade all day long. Morning sun and afternoon shade is the bestcase scenario.

Per. Ryegrass in full sun

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In full sun grasses grow vigorously and produce lots of shoots and roots.You can’t see the ground and a healthy thatch layer will be present.

Per. Ryegrass in shade

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Growing in shade, the same grass will thin out because there is not enough photosynthetically active light reaching the foliage.Sugar production decreases and there is not enough fuel to produce enough shoots or roots. Ultimately, the grass thins out.

Full Sun Shade

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Side by side it is easy to see the difference between grass growing infull sun and grass growing in excessive shade.

Reduced tillering in shade

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Once the grass thins out algae and moss tend to colonize the bare ground. This may result in surface sealing and reduced drainage. Often you end up with a slimy mushy surface.

Reduced rooting in shade

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This piece of sod has been on site for at leasta year. Notice that there are no roots growing out

from the original sod. Notice also how thin the turf foliage is. Lack of light means weak shoots and roots.

Deciduous trees screen out most of the photosynthetically active radiation

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Only certain light wavelengths are used for photosynthesis. Light passing through tree leaves is effectively filtered by the tree canopy so that the light reaching the grass contains very little photosynthetically active light wavelengths. In this case the quantity of light may be adequate but the quality is not.

Result is progressive thinning over the summer

As the season progresses turf thins out and may even die.Without enough photosynthetically active light grass simply can not grow.

Debris accumulation under conifer trees also causes thinning

Sometimes light is adequate to grow grass, but the debris from the trees tendsto bury the grass and cause severe thinning. We solve that problem by usinga bagging rotary mower to suck up debris before it can accumulate.

Pine needles build up making it difficult for grass to grow through

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Conifers of all types can drop debris throughout the year, making it very difficultto grow grass. Sometimes the best thing to do is to get rid of the grass and let the needles accumulate to form a natural mulch beneath the tree.

Failure to rake up leaves in fall results in severe turf thinning

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Deciduous trees can cause major problems in fall because most oftheir leaves fall in a short period of time and can completely cover the surface of the ground. Grass can tolerate a thick cover of leaves for only a few days. Prolonged leaf cover excludes light, stimulates disease, and encourages excessive earthworm activity. Together these can nearly wipe out a formerly dense stand of grass.

Mature trees out compete turf for moisture

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Healthy trees in lawns compete severely with the grass for moisture. This can createdry islands of weak turf around the base. Either remove turf in this zone or cut down the tree. Short of isolated watering around the tree base, there is no way to have a nice lawn in this scenario.

Tree root competition for water can be more severe than shade effects

The obvious solution here is to let the ivy spread out to the natural line where the grass is healthy. That didn’t fit with the vision of the lawn ownerso every year the dead area was reseeded, and every year the turf died!

Debris + root competition = thin turf

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Maybe turf isn’t the best ground cover for this site. The area doesn’t warrant trying to remove the needles from these mature Ponderosa pines.

Shade reduces wear tolerance

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When you add wear on top of the stress from shade, this is the result. Reality dictates that this site will never have a strong stand of grass. It isn’t really a grass problem, it is a judgment problem. Being a turf person, I would find a new spot for the picnic benches. Since this is a public park, perhaps nobody really cares one way or the other.

Annual bluegrass moves inas planted turf thins.

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Regardless of what you plant in the shade, something else is going to grow thereeventually. More often than not, it will not be what you planted. In this caseannual bluegrass which grows relatively well in the shade is moving in and replacingthe Kentucky bluegrass that does not grow well in shade. In general, if it is green and it grows in shade, I will accept it gladly.

Moss fills in when grass thins out

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Moss grows wherever other things do not grow. It has a great niche in shaded lawns and during winter often completely takes over the lawn. When summer comes, it goes dormantand grows again when the fall rains begin again. In severe shade, moss may be the only plant thatcan grow. In that case, you need to embrace the beauty of the moss or buy a chainsaw.

Poor air movement increases diseaseT Cook photo

There is more than one way to kill lawns in shade. In this case the shade weakens the turf and the wall of foliage blocks off air movement. The result is increased disease activity and a mid summer lawn failure. More light and more air movement would solve this problem.

Leaf spot

Disease often thins turf in shade

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Leaf spot diseases form lesions that eventually cause grass leaves to fall off. Turf can thin 90% or more in just a coupleof weeks if conditions are right. Shade really brings on leafspot activity. It is often devastating during the first winterafter planting.

Fusarium patch is worsein shade

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Fusarium patch often goes hand in hand with leaf spot and isalso more severe in shade. If you fertilize heavily in shade, you can plan on seeing both of these diseases.

Severe shade makesit impossible to grow functional turf

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Nature solved this problem. The tree canopy was so thick that there was never any grass growing in the entrance to this rose garden. The owner didn’t want to remove the tree so the future did not look good. Then we got a good old fashion PNW wind storm.

Removing tree increased light enough for grass to grow

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Once the tree was gone, presto, there was enough lightto grow grass. Ultimately, it is always about light. Give grass adequate light and water and it will grow every time.

Accept anything that is green in shade

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From a distance this lawn looks great! If you look close you will see lots of grasses and broadleaf plants along with moss. My advice is to enjoy it from a distance and don’t look tooclose.

Shady lawns can look good but are always fragile

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This lawn is nice in spite of the shade. It is mostly bentgrass and annual bluegrass and whilenot very dense it is still very attractive. It is also very fragile and one day of soccer from the grandkids would destroy it. You have to accept shade on its terms.

Sometimes it is wise to eliminate turf in shade

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There are grasses that can grow in partial shade

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Researchers always think they can find grasses that will do better in shade. In some cases they are successful. Our trials at OSU have taught us a great deal about growing grass in the shade.

Col. Bent + Poa trivialis Per. Rye. + Fine Fescue

Poa supina

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In the PNW, the most common shade mixtureis perennial ryegrass + fine fescue. The ryegrass helps get the stand started and the fine fescuefills out the turf over time. As you can see fromthe photo in the lower right portion of the slide,this standard mix doesn’t look very dense. In truththe standard mix fails nearly every time.

On the other hand, the Poa supina or the mix of colonial bentgrass + Poa trivialis look a bit better.None of them look outstanding and never will becausethey are growing in shade!

Better: Supina bluegrass, Poa supinaRough bluegrass, Poa trivialisAnnual bluegrass, Poa annuaColonial bentgrass, Agrostis capillarisCreeping bentgrass, A. stolonifera

Okay: Fine fescues, Festuca sp.Tall fescue, Lolium arundinaceum

Weak: Perennial ryegrass, Lolium perenneKentucky bluegrass, Poa pratensis

Grass performance in shade

Perennial ryegrass 2 lb per 1000Fine fescue 1 lb per 1000Poa supina 1 lb per 1000Poa trivialis 1 lb per 1000Colonial bentgrass 1 lb per 1000

Slice seed into existing turf or flail existing area andthen broadcast or slice seed. Plant in spring–early summer.

A shade mix for Pacific Coastal areas

First of all, this is a mix that doesn’t currently exist and that you can’t buy. Someday seed sellers will put a mix like this together perhaps, but don’t hold your breath. This mix is broad based and adaptable to a variety of shade situations. It will give you a persistent lawn that will look pretty good most of the year. For now you will have to assemble the mix by buying components and putting them together yourself. Talk to your supplier.

1) Ky. bluegrass 2 lb per 1000Fine fescue 4 lb per 1000

2) Poa supina 2 lb per 1000Fine fescue 4 lb per 1000

3) Tall fescue 8 lb per 1000

Slice seed into existing turf or flail existing area andthen broadcast or slice seed. Plant in early summer.

Shade mixes for Cool Arid areas

Shade is a lot easier to work with when you go east of the Cascades. The dry weather and the fact that grass goes dormant in winter means you don’t have as much damage from leaf spot diseases. Mix #1 will work in most shade situations, mix #2 I would use only in heavy shade, and mix # 3 is an alternative to mix # 1. I don’t like to plant tall fescue in mixtures with other grasses because it doesn’t blend well in texture. It has very goodshade tolerance in the eastern parts of the Northwest, so even by itself it is a good choice.

1. Eliminate turf in dense shade2. Remove expendable trees 3. Raise tree crowns, thin canopies

4. Raise mowing height as appropriate5. Bag clippings under messy trees6. Use least amount of N fertilizer possible7. Irrigate as little as possible8. Accept weeds and moss as okay in shade

General strategies for shady lawns

If you really want turf in shade, you need 4 to 6 hours of nearly full sun. This is no time for fantasies. Most of the time you can compromise by removing some trees, thinning others, raising crowns of some trees, and carefully picking the areas where you want to grow grass. If you want to have a dog run in a shaded area, grass is out of the question. If you can’t see the sun during the day, grass is out of the question. Use your best common sense and avoid planting grass where it doesn’t have a chance to thrive.