At the edge of the lawn the grass stands thick and deep green. Two metres further in, under the old apple tree, it thins out, then goes patchy, and then there is nothing left but moss and bare soil with a few tufts of grass in it. And every spring somebody scatters another handful of seed over it, hoping that this time it will take.
It will not take, because the seed is not the problem. Under a tree canopy several things come together, and any one of them would be enough on its own: too little light, a mat of roots that takes the water and the nutrients before the grass gets a turn, and the throughfall from the leaves, which compacts the soil and flattens the blades. On top of that comes the blanket of leaves in autumn, covering whatever is still alive.
So let us take it in order: why the light is so short, which grasses can live with that at all, how you mow and feed so they stay, and where the honest limit sits beyond which a lawn is simply the wrong surface.
At a glance
- Supina bluegrass is the real shade grass. Poa supina still holds on at around three hours of light a day, where perennial ryegrass gave up long ago. Red fescue goes with it to carry the surface.
- Mow higher, not shorter. 7 to 8 cm instead of 4. Every centimetre of blade is surface for photosynthesis, and in shade that is the bottleneck.
- Feed less than you would in the sun. Little light means little growth. Too much nitrogen makes soft blades that fungi love.
- Clear the leaves at once. Two weeks under wet leaves is enough to lose a whole corner.
- Thinning the canopy often does more than any overseeding. And under roughly three hours of light a lawn is the wrong answer. That is when you plant instead.
Why so little grows under trees
Grasses are plants of the light. They come from open steppe and from grazed land, not from woodland. Under a closed leaf canopy only a fraction of the daylight reaches the ground in summer, and what does reach it is shifted in its spectrum: the leaves above the lawn filter out precisely the wavelengths the grass uses best for photosynthesis. The grass responds the way plants in half darkness always respond. It stretches, the blades go thin, it barely puts out runners, and it stops closing bare patches by itself.
Then there are the roots. Under beech and Norway maple the bulk of the fine roots sits in the top 20 to 30 cm of soil, which is exactly where the sward roots too. On a hot summer day a large tree pulls several hundred litres of water through itself. The grass gets what is left over, and in July and August that is often nothing.
The point that usually gets missed is throughfall. A dense canopy intercepts light rain completely, so the ground below stays dry. A thunderstorm, on the other hand, collects on the leaves and comes down in heavy drops from ten metres up. That compacts the soil surface, cakes it over and presses young blades flat. Anyone who has stood under an old lime tree in the rain knows the feeling: nothing at all, then everything at once.
And then there is the special class. The horse chestnut combines a dense canopy with shallow roots and large leaves that rot slowly. The walnut roots deeply by contrast, but it casts heavy shade, and its fallen leaves contain juglone, which many neighbouring plants react badly to. Grasses take that better than vegetables do, but neither tree makes life easy.
Moss is the diagnosis, not the illness
Moss needs no strong light, no reserve of nutrients and no aerated soil. It grows exactly where the grass leaves a gap. So when a patch under trees goes mossy, the moss is only telling you that the grasses cannot compete there.
That is why scarifying in tree shade so rarely achieves anything lasting. You tear the moss out, the light stays the same, and by the next damp autumn it is back. What helps instead is in scarifying against moss.
The mixture decides: supina bluegrass and red fescue
In the garden centre there is a bag with "shade lawn" on the label and a birch tree on the picture. What is actually inside is printed small on the back, and that is exactly the difference between a patch that holds for years and one that disappears again in the first dry summer.
The real shade grass is supina bluegrass, Poa supina. In the wild it grows on alpine cattle resting grounds, it takes foot traffic, it recovers from creeping runners, and it manages on around three hours of daylight. It is expensive, because the seed is laborious to produce, and it germinates slowly, often only after ten to 21 days. Both are the reason cheap mixtures contain it in homeopathic amounts or leave it out altogether. Cultivars such as supina bluegrass ‚Supranova‘ have been proven on sports pitches for years.
One point the copy on the bag leaves out: supina is the most demanding component of the mixture. It has a high demand for water and nutrients, it reacts badly to drought, and in winter it is prone to snow mould. If you sow it, you have to water in dry spells and feed regularly but in small portions. Otherwise the most expensive ingredient is the first to disappear, and after two summers the mixture looks worse than your care actually was.
The second important partner is red fescue, Festuca rubra, in its subspecies. It is modest about nutrients, roots deeply and carries the surface while the supina closes the gaps. Wood meadow-grass, Poa nemoralis, is added in landscape mixtures for partial shade, but it takes almost no foot traffic.
How to spot a shade mixture worth buying
- Supina bluegrass is on the listWithout supina (Poa supina) it is not a real shade mixture. The German standard mixture RSM 2.3, officially "utility lawn, play lawn with Poa supina", contains only 5 % of it plus around 30 % perennial ryegrass. It is the floor, not the target. Mixtures sold specifically for shade go up to 20 to 30 %.
- Red fescue carries the surface40 to 50 % red fescue across several subspecies is a good sign. It forgives poor soil and dry spells, and it makes a fine sward.
- Little perennial ryegrassLolium perenne germinates fast and looks magnificent in week three. In shade it dies out after the first dry summer and leaves behind exactly the gaps the moss then sits in.
- A mixture code or a list of cultivarsIf there is a standard mixture code on the pack, or the cultivars are named, you know what you are buying. "Various grasses" is not information. For extensively used areas in partial shade there is also RSM 7.4, the landscape mixture for partial shade, built around wood meadow-grass.
Count your hours of light instead of guessing
On a clear day, stand in the same spot and photograph the ground every 30 to 60 minutes, from sunrise to sunset. A time lapse or the interval setting on your phone does the work for you. In the evening the pictures show you how many hours of real sun arrive there. Moving dappled light through the canopy counts as half. The low morning and evening light counts too, and it is precisely the part that lifting the crown gives back. This is the one number everything else hangs on, and it is almost always fewer hours than you would think.
Overseeding: use the late summer window
For shady spots late summer is the better season. The soil is warm, the nights turn damp, evaporation drops, and the leaves have not fallen yet. The window runs from roughly mid August to mid September, so CW 33 to 38. If you want to lay a surface out completely from scratch, you also have the spring window in CW 14 to 20.
Clear the surface
Rake off leaves, windfall fruit and old thatch with a springbok rake until you can see soil in several places. Do not scarify if you are working in the root zone of a tree. The blades cut through the fine roots near the surface, and the tree needs those.Open the soil only at the surface
With a hand rake, scratch the surface open 1 to 2 cm so the seed gets soil contact. Do not dig it over. Nothing more is needed.Add a little substrate
A thin layer of sand and ripe compost, 1 to 2 cm, improves the seedbed. Never heap more than 5 cm of material over tree roots.Sow thickly
20 to 25 g of seed per square metre when overseeding, in two passes at right angles to each other. Then firm it down with a roller, a board or your feet. Do not bury it, grass seed needs light to germinate.Keep it damp for three weeks
This is where most overseeding fails. The surface must not dry out, which in warm weather means a brief spray every day rather than one flooding. Rain hardly gets through a canopy, so do not rely on the sky.Mow only once it reaches 10 cm
Then take it back to 7 cm, with a sharp blade so the soft seedlings are not pulled out of the ground. Keep off the area as much as you can in the first few weeks.
Soil temperature matters more than the date
Supina and red fescue germinate reliably from around 10 °C soil temperature, and briskly from 14 °C. A kitchen thermometer pushed five centimetres into the soil is measurement enough. After CW 38 it gets tight, because the young plants need around six weeks to root before the first frost.
Overseeding rescues a surface that still carries grass over at least half its area. If more than half is moss or bare soil, you are working against the light rather than against the gaps. The general technique is covered in more detail in overseeding a lawn with bare patches.
Care: higher, leaner, free of leaves
A shade lawn does not get better with more effort, it gets better with different effort. The most important adjustment costs nothing beyond a turn of the dial on the mower.
Cutting height 7 to 8 cm. In the sun 4 cm is plenty, in shade that is too short. Every extra centimetre of blade is more leaf area, and here everything hangs on that. During the season you should not take a shady surface below 5 cm, and mixtures dominated by red fescue prefer 7 to 8 cm. Never take more than a third of the blade length per cut, so with a target height of 8 cm you mow at 12 cm at the latest. How that fits together across the year is in mowing a lawn properly.
Less nitrogen, and potassium in autumn. Little light means little growth, and little growth needs little nitrogen. Two nitrogen applications are usually enough in shade, one in April and one at the end of July, each at roughly half the amount you would put on a sunny surface. Because supina is hungrier than red fescue, spread that across small portions rather than one big load. Add a potassium heavy autumn feed in September with almost no nitrogen: potassium raises the cell pressure in the blades, which improves winter hardiness and lowers the risk of snow mould. Red thread, on the other hand, that pink web of threads on the leaf tips with straw coloured patches, is a sign of nitrogen shortage. There a moderate nitrogen application helps, not less fertiliser. The full schedule across the year is in feeding a lawn through the year.
Leaves off straight away. Under wet leaves the grass loses light and air at the same time, and after ten to 14 days the patch underneath is yellow. In October and November that means raking every three to four days, not once at the end of the season. Large flat lying leaves from maple, plane and chestnut are the trickiest. The leaves then go not into the bin but into leaf mould or under the hedge.
Do not forget the water. In summer the soil under a canopy is regularly drier than the open lawn, even though it is cooler there. In long dry spells water deeply and rarely, so the whole root zone gets wet rather than just the top few millimetres, which the tree pulls away immediately.
Heaping soil over tree roots can kill the tree
The idea sounds logical: a layer of good soil over the root plate and then the grass will grow. In practice the fine roots underneath suffocate, because they lose their gas exchange. On sensitive species such as beech 10 to 15 cm is enough to do it, and the damage only shows two or three years later in dying parts of the crown. So no more than 5 cm of fine, free draining material, and never spread right up against the trunk.
Thinning the canopy often does more than any overseeding
Every care trick works at the edge of the problem. The light itself is only changed by pruning in the canopy. A thinning cut takes out branches growing inwards, branches rubbing against each other and dead wood, and it makes the crown permeable. Add to that lifting the lowest tier of branches: that lets the low morning and evening light fall onto the surface. On an old apple tree that is often two hours more light a day, and suddenly the surface sits in a range where supina genuinely performs.
Rule of thumb: no more than about a fifth of the crown volume in one season, otherwise the tree answers with dense watershoots and the second year is shadier than before. For fruit trees the approach is in pruning fruit trees: the basics of the winter cut. For large trees, where you would need a ladder or rope access, this is a job for a tree surgeon and not for a Saturday afternoon.
Keep the nesting season and local tree bylaws in view
In a domestic garden, maintenance and shaping cuts on trees are permitted in the summer half year too; the closed period from 1 March to 30 September under Section 39 of the German Federal Nature Conservation Act does not apply in that form on land used as a garden. That holds for Germany, and only for trees, not for hedges in the garden; in Austria and Switzerland the state and cantonal rules set their own dates. Independently of all that, Section 44 forbids any disturbance of nesting birds, so in the summer half year always look into the crown first and put the saw in afterwards. Many towns and councils also have a tree protection bylaw requiring consent above a certain trunk girth, often from 60 to 100 cm, measured at one metre or at 1.30 m depending on the bylaw. A phone call to the parks department settles both in five minutes.
Under three hours of light a day no grass wins. That is where the lawn ends and the garden begins.
Gartenkern rule of thumb for shady sites
When a lawn is the wrong surface
There are corners you will not win. A north side, a dense group of spruces, two hours of dappled light in June and none in September. Scattering seed there every year is an expensive habit.
Waldsteinia, also sold as golden strawberry, covers such ground permanently with leathery, winter green leaves, flowers yellow in April and needs almost no care once established. It is walkable in the sense that you can cross it once a week. It will never be a five a side pitch.
Alternatives for real shade
Moving from lawn to planting is not a defeat, it is the point at which a corner like that finally looks good. What reliably performs in deep shade under trees:
- Waldsteinia (Waldsteinia ternata), a dense carpet spread by runners, tolerates root pressure. Around eight to ten plants per square metre.
- Barrenwort (Epimedium), the toughest choice directly under trees, because it copes with dry shade. Cultivars such as barrenwort ‚Frohnleiten‘ hold their leaves through winter, and in February you cut them off close to the ground.
- Hostas (Hosta) for the damper, slightly brighter spots. Blue leaved cultivars such as hosta ‚Halcyon‘ are, in practice, less prone to slugs than thin leaved ones. Details in hostas in the shade garden.
- Ivy (Hedera helix) for areas nobody walks on. So robust that it eventually becomes too much of a good thing, so keep an eye on the edge and do not let it run up the trunk on young trees.
- Lesser periwinkle (Vinca minor), bigroot geranium (Geranium macrorrhizum) and foam flower (Tiarella cordifolia) for the mix, plus male fern in dry shade. Ostrich fern and sweet woodruff only where the soil stays reliably moist, because both spread strongly by runners.
- Bark mulch with stepping stones, where people genuinely walk. 5 cm of coarse bark mulch, no more than that over tree roots, tipped on loosely rather than trodden down, and the stones set at a stride of about 60 cm. Scatter a thin dose of horn meal first, because fresh bark mulch locks up nitrogen while it rots. That is the honest solution for the path around the trunk.
One note on the selection: ivy, periwinkle and male fern are poisonous, ivy berries in particular. Where small children play, Waldsteinia, hostas, barrenwort and foam flower are the safer choice.
In practice you go about it like this. Draw the lawn edge not along the drip line of the canopy but a good way further out, in a soft curve. Inside that line goes the planting, outside it the lawn stays, and you can mow it in one pass. That looks intentional rather than like a retreat, and the mower no longer has to steer around the trunk.
When planting between tree roots you do not dig the whole area over, you set each perennial into a pocket between the strong roots. Small root balls are an advantage here, and the big roots stay where they are. Then two or three centimetres of leaf mould as a cover, more on that in mulching: protecting the soil. Water through the first year, after which the species named look after themselves.
What to do in what order
If you start tomorrow, the order matters more than the choice of products. Measure the light first, then deal with the canopy, then buy seed. Turn that around and you buy seed three times and wonder why.
- Count the hours of light, on a clear day with the canopy in full leaf, with photos.
- At four hours and more: thin the canopy if you can, and overseed in late summer with a supina mixture.
- At three to four hours: thinning is compulsory, then overseed with a high proportion of supina, hold the cutting height at 7 to 8 cm permanently, and lower your expectations a notch.
- Under three hours: repurpose the area, either shade perennials or a mulched surface with stepping stones.
The shade under a tree changes over the years. A canopy that cast partial shade five years ago makes full shade today, which is why a surface like that is hard to judge from memory. Put the thinning cut and the seeding window into your garden diary as recurring tasks, and add a photo of the spot every June. After two summers the pictures side by side show you whether it is getting better or whether it is time for hostas.
Common questions about lawns under trees
Which grass mixture works for shade under trees?
One with supina bluegrass (Poa supina) and a high proportion of red fescue (Festuca rubra). The German standard mixture RSM 2.3 contains only 5 % supina plus around 30 % perennial ryegrass, so it is the floor rather than the goal; mixtures sold specifically for shade go up to 20 to 30 %. Always check the back of the pack: if it says only "various grasses", or lists mostly perennial ryegrass (Lolium perenne), the seed germinates fast and is gone again after one summer. Reckon on 20 to 25 g per square metre when overseeding.
How high should I mow a shade lawn?
7 to 8 cm during the season, so almost twice as high as on a sunny surface, and not below 5 cm. A third of the blade length is the upper limit per cut: if the area has gone unmown for two weeks, bring it down in two passes rather than one. The last cut in late October or November goes back to around 5 cm, though, so that the long blades do not fold over and rot under wet and snow. Supina is prone to snow mould, and leftover leaves in a tall sward are exactly the combination it wants.
When should I overseed a shade lawn, spring or autumn?
In shade late summer is better: roughly mid August to mid September, CW 33 to 38. The soil is warm, the nights are damp, the leaves have not fallen. The spring window in CW 14 to 20 works too and has the advantage that the deciduous trees are not yet in full leaf. In tree shade it only becomes usable once the soil holds 10 °C, though, so realistically from late April. And it demands more watering, because the tree gets going in May. Important either way: the seed has to stay damp for three weeks without a break, and supina germinates slowly.
Why does no grass grow under my birch?
Birches have a very dense, shallow net of fine roots and take water and nutrients away from the grass right at the surface. On top of that comes the canopy, which looks airy but moves shade across the surface constantly in wind, and in autumn a fine layer of leaves that mats together. What helps most there: mow higher, water in summer as well, clear the leaves at once. If that is not enough, a planted area with barrenwort and ferns is the lasting and better looking answer.
Does lime help against moss in a shade lawn?
Only if the soil really is too acid, and you only know that from a soil test. The target range depends on the soil type: on sand not below pH 5.5, on medium soils not below 6.0, on loam and clay not below 6.5. The soil test names both, the pH and the soil type. Moss does not grow because of the pH anyway, it grows because the grass leaves a gap: too little light, compacted soil, too short a cut. Spreading lime on a shady surface without changing the cause just moves the problem on by a season.
What can I plant under trees instead of lawn?
For permanent shade, Waldsteinia, barrenwort, lesser periwinkle, bigroot geranium and foam flower work as a covering carpet, with hostas and ferns for structure. Ivy is the most robust option for areas nobody walks on. Where people do walk, a mulched surface with stepping stones is the most practical solution. Plant into pockets between the strong roots rather than digging the whole area over, and water regularly through the first year.
Sources and further reading
- Overseeding a lawn with bare patches
- Mowing a lawn properly
- Feeding a lawn through the year
- Scarifying against moss
- Hostas in the shade garden
- Using autumn leaves: leaf mould
- Mulching: protecting the soil
- Pruning fruit trees: the basics of the winter cut
- Plant profiles: Waldsteinia · Barrenwort · Hosta · Ivy · Lesser periwinkle · Bigroot geranium · Foam flower · Male fern · Ostrich fern · Sweet woodruff
- The RSM standard seed mixtures for lawns published by the German Research Society for Landscape Development and Landscape Design, together with the cultivar recommendations of the German Turfgrass Society
The legal side of tree pruning
Pruning work on trees can require consent. Many councils in Germany, Austria and Switzerland have their own tree protection bylaws with thresholds for trunk girth and crown reduction. In rented property and allotment sites, tenancy and lease agreements apply on top. Clear larger interventions with the responsible authority before the first cut, and for trees beyond ladder height with a tree surgeon.
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