Mountain Laurel Care: Water, Mulch and Leaving the Pruners Alone

What this shrub actually needs

Mountain laurel is one of those plants that is either easy or impossible depending entirely on the ground it is in. Given genuinely acid, moisture-retentive, freely drained soil it grows steadily for decades with almost no attention. Given anything else it sulks, yellows, thins out and dies back over several years while looking, at each individual stage, as though it might be about to recover. It rarely does.

So the care regime divides into two very unequal parts. Getting the conditions right is nearly all of the work, and most of that is done before or at planting. The ongoing routine that follows is genuinely light: water in dry spells, top up the mulch once a year, deadhead after flowering, and otherwise watch it.

It is also extremely slow. Two to six inches (5 to 15 cm) of extension a year on an established plant is normal, and a shrub takes fifteen years or more to reach the six to eight feet (1.8 to 2.4 m) it will eventually hold. That slowness is why intervention is so costly here: everything you remove takes years to come back, and everything you get wrong stays visible for a long time.

Water: the fault line of the whole plant

The root system is a dense mat of very fine roots sitting in the top six to ten inches (15 to 25 cm) of soil. It holds no reserve at all. A fortnight of genuine drought in midsummer is enough to brown the leaf margins, and because that is exactly when the flower buds are being formed at the shoot tips, you also pay for it the following spring with a thin display.

The same fine roots drown easily. A shrub in heavy soil that copes perfectly well through summer can be killed by six weeks of standing water between autumn and spring, when there are no leaves transpiring and the ground never dries. That combination, needing constant moisture but never wet feet, is why the mulched, humus-rich, freely drained root run matters so much and why a bare clay bed almost never works.

Water by volume rather than by habit. A soak that wets the whole root plate to eight inches (20 cm), given whenever the top two inches (5 cm) under the mulch have dried, is worth far more than a daily sprinkle, which only wets the mulch surface and encourages the roots to sit shallower still. On an established plant that usually means one thorough soak a week through a dry spell.

Use rainwater where the mains supply is hard. Dissolved calcium in tap water slowly lifts the pH of the root zone, and on a shrub this fussy about pH that is a real effect over a few seasons rather than a theoretical one.

1. Test under the mulch, not on top Push a finger through the mulch layer into the soil. The mulch surface is always dry and tells you nothing. If the soil two inches (5 cm) down is dry, water.
2. Soak the whole spread slowly Deliver around two gallons (8 liters) per square yard (square meter) of root spread, slowly enough that nothing runs off. Move around the drip line rather than pouring it all at the stem.
3. Keep three inches (8 cm) of mulch on Composted bark, pine needles or leafmould over the whole root area, pulled back an inch or two from the stem. Top it up every spring as it breaks down.
4. Never hoe or fork around it The working roots are in the top few inches and cultivation cuts them. Suppress weeds with mulch and pull by hand anything that comes through.
5. Check winter drainage after heavy rain Walk out during a wet spell and see where water stands. If it lies over the root run for days, the long-term answer is a raised bed rather than more work at ground level.
6. Water once after a dry autumn Evergreen leaves keep losing water all winter. Going into a freeze with dry soil is what browns the foliage. Soak thoroughly before the ground hardens.

Feeding, light and the pruners you should not pick up

This is not a hungry shrub, and overfeeding does more harm than neglect. A single application of slow-release ericaceous fertilizer as the buds begin to move in spring covers a whole year, and on ground that is properly acid and annually mulched you can skip it entirely. Leafmould and composted bark laid on the surface feed it slowly while improving the moisture holding of exactly the layer the roots occupy, which is the more useful contribution. Never use garden lime, mushroom compost or any general fertilizer containing lime anywhere near it.

For light, aim for bright conditions with relief from the strongest sun. In cool-summer climates it takes full sun happily and flowers most heavily there. Where afternoons run above 85F (30C), morning sun with afternoon shade keeps the evergreen leaves from bleaching and scorching. Deep shade is the one setting to avoid outright: the plant survives it but flowers sparsely and grows thin and drawn.

On pruning, the working rule is that you deadhead and you remove dead wood, and that is all. Mountain laurel breaks from old wood reluctantly and slowly, so a hard cut leaves a gap that can take five years or more to close. If a plant genuinely must be reduced, take out no more than a quarter of the oldest stems in any one year, cutting them low, and spread the job over three or four seasons. Do it in the short window straight after flowering, never in autumn or winter, when the shoot tips are carrying next spring's buds.

A plant that is bare at the base and flowering only at the top is usually telling you about shade rather than about age. Renovation will not fix that, and letting light in around it, or moving it while dormant, gives a better shrub far sooner.

The flowers, and what makes them worth going out to watch

The buds are the reason many people grow this plant even before it opens. They stand in tight clusters as deeply ribbed, angular little cones, looking exactly like piped icing on a cake, and they hold that shape for a fortnight or more before anything opens. On a well-set plant the effect at that stage is as good as the bloom itself.

The open flowers are a shallow cup, and each one holds its ten stamens bent back with the anther tips tucked into small pockets in the petal wall, under tension like a set loaded spring. When an insect of the right weight lands on the flower and pushes into it, the anthers snap free and flick a puff of pollen upward onto its back. It is quick, and you can trigger it yourself with a blade of grass or a fine brush, which is worth doing once on a warm morning simply to see it happen. Each flower fires only once, so pick a truss you are not counting on.

Flowering runs for two to three weeks in late spring to early summer, later on plants in shade and shorter in hot weather. Once it is over, the deadheading window opens immediately.

Keep a short annual record: the date the buds first show color, the date the first flowers open, the date the last ones brown, and one line on how heavy the display was. Those dates barely move from year to year in a given garden, and after two seasons they tell you exactly when to be ready with your hands for the deadheading rather than having to check the plant daily.

Every part of this shrub is seriously poisonous, to people, to pets and particularly to livestock, and the toxins survive in dried leaves and clippings. Bag prunings and deadheaded trusses and dispose of them where grazing animals cannot reach them. Do not compost them into a heap that will be spread on a vegetable bed, and do not burn them where the smoke blows over people or animals.