By: Mary H. Dyer, Credentialed Garden Writer
Mountain laurel is a broad-leaved evergreen shrub, native to the United States where it is much beloved. Mountain laurel usually remains green year round, so brown leaves on mountain laurels can be a sign of trouble. The following information may help.
Below are the top reasons for brown leaves on mountain laurels:
Desiccation/winter burn – Brown leaves on mountain laurels can be caused by desiccation, which occurs when winter wind draws moisture from the tissues. If the plant is unable to pull moisture from the soil, the water in the cells isn’t replaced and leaves turn brown. To prevent desiccation, ensure the tree is properly watered during dry periods.
Cold temperatures – Damage can occur when winter temperatures are unusually cold, but it is most likely to occur in trees planted in the northern borders of their USDA hardiness range. An organic mulch will help during the winter. If necessary, protect mountain laurel trees with a burlap windbreak.
Improper watering – Brown mountain laurel leaves, primarily when browning shows up at leaf tips, may be due to improper watering or excessively dry soil. Always water the tree deeply every seven to 10 during absence of rain by allowing a hose or soaker to soak the ground for at least 45 minutes. A layer of mulch will keep the soil evenly moist but be sure to leave a span of bare ground around the stem.
Fertilizer burn – Strong chemical fertilizer may be the reason for mountain laurel leaves turning brown, especially if discoloration affects the tips and edges. The tree may be absorbing too much fertilizer without your realization if it’s planted close to a heavily fertilized lawn. Follow fertilizer manufacturer recommendations closely. Never fertilize dry soil or a thirsty tree.
Sunburn – When mountain laurel leaves are browning, it may be because the tree is exposed to too much intense, direct sunlight. Mountain laurel shrubs prefer plenty of morning sunlight but should be in shade during the afternoon.
Drought – Established mountain laurel trees are relatively drought tolerant, but they aren’t likely to tolerate long periods of extreme drought. Mulch is critical to help mountain laurel trees survive drought and summer heat.
Disease – While not often an issue, mountain laurel shrubs do suffer from occasional fungal problems, especially in areas with abundant humidity and moisture. Leaf spot is the most common of these and will cause browning of the leaves. Fungicides can help.
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Leaves Turn Yellow means Soil Too Alkaline
When acid loving plants are in soil that is too alkaline they develop a condition called chlorosis. The yellowing of their foliage is a signal that they need more acid in their soil. This sometimes happens when shrubs are planted near masonry walls and over time the rain leaches lime from the mortar into the soil. To acidify soil, add peat moss or aluminum sulfate to it. Do not use lime near mountain laurels.
Leaves Turn Brown in Winter Shows Winter Burn.
Mountain laurels that are exposed to bright winter sunlight and harsh winds often develop winter burn on their foliage. Their leaves dry out, turn brown, and will eventually drop. Minimize this danger by siting shrubs carefully when planting them. Spray foliage with anti-transpirant just before cold weather sets in and shield exposed shrubs with a burlap windscreen.
Foliage Turns Pale Or Mottled indicates Lace Bug.
Adult rhododendron lace bugs are small square-shaped bugs, 3/16 inch long or less, with elaborately reticulated wings that resemble lacework. They suck sap from the undersides of mountain laurel leaves, causing them to turn pale or mottled. This sucking insect appears in late June and in the summer on the undersides of the leaves of broadleaf evergreens like azalea, rhododendron and mountain laurel. Control light infestations by crushing the bugs. Pinch the leaves on which they are feeding between your thumb and forefinger. Treat heavier infestations by spraying the bugs on leaf undersides with insecticide.
For more information see the file on Dealing With Lace Bugs
Branches Wilted Stems With Borer Holes means Rhododendron Borer.
The borer is a yellowish larva (worm), about 1/2 inch long. They over winter as partly grown larvae in burrows in mountain laurel stems. Adults emerge in June, and lay eggs on leaves, new twigs, or rough bark of the main stem. They sometimes girdle branches when laying their eggs, causing tips to die back and break off. They enter into the tips of stems and bore out some of the twigs soon after blooming time. As they get larger, these larvae bore into the woody part of the laurel shrub, pushing out fine sawdust as they go. When its main stems are bored, ugly scars remain and sometimes-large branches die.
To control borers examine the mountain laurel before the spring season arrives and cut and burn any dying stems below visible borer holes. In June, crush any eggs that you can find. During the summer season, check to see if fine boring dust is being pushed from small borer holes. Cut out these holes with a sharp knife. If the tunnels are fairly straight, probe in them with a flexible wire to kill the worm inside, or pull it out by means of a hooked wire to make certain it is destroyed. Borers can also be killed with nicotine sulfate. Dip a piece of cotton or soft cloth into a solution 1 part nicotine sulfate to 4 parts water, and stuff it into the borer's hole or try injecting nicotine paste into the holes.
Another approach is to introduce BT (Bacillus thuringiensis) into each hole at ten-day intervals until no more telltale sawdust appears. A special hypodermic needle for injecting BT is commercially available. Coat or seal wounds with tree paint, putty, paraffin, or chewing gum. A black light trap may prove effective against the adult borers, if used in May or June when the insect is in the moth stage. Practice garden hygiene and burn all weeds, stems and plant remains likely to harbor over wintering eggs.
For more information see file on Dealing With Borers
Leaves Turn Yellow Weak, Dying Branches appears to be Weevil.
Black vine weevil adults are brown beetles with long snouts. They have tear-shaped and hard-shelled bodies, averaging 3/8 inch long. They feed on foliage and bark, leaving characteristic notches along the edges of mountain laurel leaves. Weevil larvae, white grubs with brown heads, also feed on laurel roots deep in the soil. These pests are hard to spot because they feed at night, living under tree bark and debris on the ground by day.
Because these weevils "play dead" when disturbed, folding their legs and dropping off plants to the ground, they can be trapped. Gently beat the branches of the infested shrub and catch the startled insects when they fall onto a cloth spread beneath the shrub. Apply tanglefoot to the trunks of the shrub to prevent the adults from climbing up and eating the leaves. As soon as weevils appear, begin spraying weekly with a pyrethroid insecticide which is a synthetic insecticide.
For more information see file on Controlling Weevils
Dead Blotches on Leaves means Leaf Spot.
Various leaf spot fungi cause yellow, brown or black dead blotches on mountain laurel leaves. These blotches frequently run together, causing heavily infected leaves to turn yellow or brown and fall prematurely. Cool, moist weather encourages these diseases, especially when new leaves are developing. Shake out all fallen and diseased leaves from the center of each laurel shrub and destroy them. Remove all dead branches in the center of individual plants or hedges to allow better aeration. Mulching helps prevent the disease from splashing up from the ground and infecting plants. Spray at weekly to 10-day intervals with sulfur or copper fungicide, particularly in rainy weather. Dig up and discard seriously infected shrubs together with the root system and soil ball.
For more information see file on Controlling Fungal Disease.
Do you have a gardening question? Ask Nancy
Yellowing is a sign of stress and on Laurel is is normally either mineral deficiency or over or under watering or a mix (over watering causes minerals to wash away). I would add a good feed around the plant - use liquid and pellet versions. If it is getting water logged then you need to fork around the area to imporve drainage.
Hello John - I agree with blairs regarding mineral deficiency - possibly magnesium needed (your local garden centre can advise you) . Also check your soil type is not too chalky as the laurel will not thrive. To make it bushier, prune the leading shoots by about one third- cut them cleanly just above a leaf joint.
There are so many commercial preparations available that my advise to you would be to go to a good garden centre where you will find products - usually containing magnesium or manganese sulphate - which will say ' for yellowing of the leaves'.They will have instructions on how to use. Also, if you take one of the leaves with you a member of staff should be able to help you further. Do bear in mind though, that you may have to keep the treatment up continually throughout the lifetime of the plant and you may wish to consider an alternative - I landed up getting rid of several large laurels because they were never going to look good and were continually loosing the older leaves that they just looked unsightly. Good luck!
I too have planted new laurels, I removed some previous yellowing plants and replaced them, but it's still happening It is a hedge I have and only part of it has gone yellow, we put in bonemeal and soil improver before planting, magnesium.
Linda in Switzerland (ex Brighton girl. now aging gardener)
Such a relief to hear that my laurel hedge, which had, after 9 years now reached maturity, may only need magnesium (have been taking that myself..should have given it to the laurel.) The hedge has been losing its leaves copiously over the last 2 months and they turn yellow before dropping. The hedge now looks like a doily with all the foliage disappearing. Here in southern CH we had a very hot summer (35° most of the time) and now we have had about 2 months with almost no rainfall.
I also find that, when new foliage starts to sprout in the spring the new leaves are fine for a while and then, every year, they get a mold and start curling at the edges. Any suggestions? What can one do during the winter months to ensure healthy growth in the spring?
Hi, hopefully I've found a site that can offer some advice on my Laurel hedge. I have around 90 plants that are forming a barrier between my home and a public footpath. They were planted by a professional around 18 months ago and were approximately 6' from root to tip. During this time they have been fed, and trimmed 3 times. They now stand around 8' but dont seem to be thickening out which is why I chose this plant in the first place. It seems that every day I look at them they appear different in colour, thickness, amount of foliage. They have lost quite a lot of leaves in the last 2 months which then makes them look very sparse. I also have a climbing weed that flowers at ether top in the shape of a white horn. My question is, how can I get them to thicken out and what sort of care should I apply to keep them healthy And is this weed affecting them?
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Over time, soil surrounding the tree's roots can be tamped down by the elements or by people walking over the area. This interferes with proper drainage, and mescal bean trees hate wet feet. Try checking the soil drainage as described, and working in some organic matter if the soil is workable. Mulch the root zone with hardwood shavings, but don't allow the mulch to touch the tree's trunk. The mulch keeps the roots cooler, and improves drainage and soil quality as it decomposes.
Dear Neil: My mountain laurel’s leaves turned brown in a matter of weeks. How did the fungus take hold? The small tree had been healthy for years. If I replant, what preventive measures should I take for a young plant?
Your e-mail pre-dates the extreme cold by a couple of days, so I can discount that as a cause. I don’t want to jump to the browned leaves and leaf spots as being the original cause of this problem (although I don’t have any better idea just yet). I would be more likely to suspect a trunk or root problem. I’m grasping at straws, but it appears that the walk is water-stained adjacent to the plant in your photo. Is there any chance that this plant has had water dripping around it for a prolonged period of time from the hose hanging on the wall? That could have caused it to die by killing its roots due to lack of oxygen. If you feel the plant has been lost (it appears that that’s the case), you might want to send a portion of the base of the trunk and a major root and some of the smaller roots to the Texas Plant Clinic at Texas A&M University in College Station and ask them to look at it. There is a charge for their analysis, but then you would know for sure. All the details are at their website. As for replanting, I would probably choose another type of plant just to be on the safe side.
Dear Neil: You often recommend eastern redcedar and other junipers for landscape screens. Are those the same plants as the “mountain cedars” we hear in the allergy reports?
In many cases, yes. Eastern redcedar (Juniperus virginiana) is the native conifer that grows over huge parts of Central and East Texas. There are thousands of acres that are covered with it and other species of junipers. They turn bronze and produce pollen from mid-winter into early spring and warm south winds push the pollen across the state. But lest you grab you grab your chainsaw and start taking out all your junipers, let me share a personal opinion. My wife suffers this seasonal allergy. Sprays help her immensely, and so I have left the 40 or 50 mature trees we have on our rural property in place. I even planted several more years ago to act as a critical privacy screen since I knew they would blend in and maintain the natural look. I figured the pollen those 15 trees would produce wouldn’t add much to the overall pollen count produced by the millions of other trees in the hundreds of miles around us. (That’s how far wind-borne pollen will travel.)
Dear Neil: I’ve been reading about ajuga as a flowering groundcover for the shade. Have you grown it, and would you recommend it in Texas?
Yes, I’ve grown it for 50 years, and yes, I’d recommend it, but with one very major precaution. It is a lovely low-growing groundcover for heavily shaded areas. That alone makes it really special. We don’t have that many good groundcovers for shade. The fact that it blooms makes it all the more special. The flowers, on most varieties, are stunning rich blue, one of the least common colors in the Plant Kingdom. And it spreads quickly, at least most selections do. But the problem is that it’s also highly susceptible to crown rot, a water mold fungus that can wipe out an entire planting in just a couple of weeks. I know, because my planting of bronze ajuga that I had propagated myself was struck by it and killed out completely in a 5-day period. I couldn’t get to the store, buy a fungicide and get it applied fast enough. I was out of the ajuga business before I knew it. I still grow ajuga, but I’m careful to plant it in perfectly draining soil, and I limit my plantings to small areas such as rock retaining walls and between stepping stones in little-used garden paths. It has thrived in those settings for 25 years.
Dear Neil: How soon will we be able to assess the damage the cold did to our landscape plants? What should we do to the ones that have turned brown?
Don’t rush to a judgment. If they have browned leaves, it’s possible that new leaves will be produced to replace them. You might have only minor dieback on some of the twigs with just a little pruning and reshaping to do. On the other hand, some shrubs will have been killed completely to the ground. That’s going to happen to oleanders in big parts of Texas, for example. Their twigs will turn brown along with the leaves, so you’ll have quick indication of the magnitude of your problems. With those plants, folks will have to cut them back completely to the ground. They will come back with robust growth from their roots. Other plants that are killed to the ground may not come back at all. Pittosporums in many parts of Texas fall into that category. So will star jasmine and loquats where they are grown. So, my suggestion at this point, because Texas is such a big state and because so many plants are involved, is that you just sit tight for a couple of weeks. As stem tissues turn brown and brittle, you’ll know they can be pruned off, but don’t rush to bad decisions.