Moss and shady lawns

The shaded strip under a tree is the part of the lawn people fight hardest and lose most often. Extension guidance for turf in shade is specific, and it starts by changing four things about how you manage that area rather than what you apply to it.

Moss first, because it is misunderstood

That is the same logic extension weed guidance applies more broadly: find out the reasons behind the invasion before treating it, because treating without correcting only invites continued and increased invasion. Moss is simply the clearest example.

The four things extension guidance changes in shade

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Matching species to shade level

Penn State separates shade into three levels with a different species answer for each, which is more useful than a single "shade mix" recommendation.

Fine fescues come with a published trade worth planning for: Penn State rates their wear tolerance as poor and notes they are not typically used for sports turf or high-traffic areas. A shaded fine-fescue area is also an area to route foot traffic away from.

They are also the lowest-input species in the table, at a published 1.0 to 2.0 lb of nitrogen per 1,000 sq ft per growing season against 2.0 to 4.0 for Kentucky bluegrass.

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The tree side of the problem

Shade is only half of what a tree does to a lawn. The other half is root competition for water and nutrients in the same soil volume, which is why the watering advice for shade is counter-intuitive.

Penn State's guidance on the trees themselves is direct: remove those trees that are not essential to the beauty, prune tree branches as much as possible without destroying their aesthetic function, and prune shallow tree roots as much as possible.

When to stop growing grass there

The most useful sentence in the shade guidance is the one that gives you permission to stop. Penn State: use other types of ground covers where environmental modifications are difficult, or the cost is prohibitive, naming periwinkle, pachysandra, purple wintercreeper and English ivy as suitable.

• The area has been reseeded twice and thinned out both times
• Canopy thinning is not possible or not wanted
• It is under a mature evergreen, where shade is dense and year-round
• It is a narrow strip that also takes traffic
• You are watering it separately from the rest of the lawn to keep it alive

A mulched bed or a groundcover in that strip is less work, looks deliberate, and stops you buying seed for it every autumn.

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A shaded-area routine

1. Raise the deck about an inch for that area, if the mower can reach it.
2. Water deeply and infrequently, the same as the rest of the lawn.
3. Feed slightly above the species rate, at a 2-1-1 or 1-1-1 ratio with 30% or more slow-release nitrogen.
4. Overseed with fine fescues in the late-summer window rather than in spring.
5. Keep traffic off it, because fine fescues are poor on wear.
6. Thin the canopy if you can, which changes the shade level and therefore the species options.
7. Give it two seasons. If it still fails, plant a groundcover.

What we cannot tell you

Penn State's shade guidance does not state a minimum number of hours of sunlight turf needs, so neither do we. We also will not recommend moss-control products; that is regulated and regional, and the conditions are the actual target anyway.

What is published: mow about an inch higher, never remove more than a third of the leaf surface, water deeply and infrequently, feed slightly above the species rate at 2-1-1 or 1-1-1 with 30% or more slow release, choose fine fescues, and use groundcover where modification is impractical.