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Plant Answer Line Question

Keywords: Prunus laurocerasus, Plant diseases--Diagnosis

I am losing leaves on my improved English laurel. They turn bright yellow and fall off. I have heard that some loss is normal, but I have one bush losing at least 15 leaves. They have been in the ground now for 4 weeks.

Second question if I could? When a plant turns yellow from the bottom but the top looks normal and wants to bloom what is the problem. Too much water, etc. It just a small flowering plant and the bottom is getting yellow like it is not happy but the top wants to grow fine.


I will take your second question first: When the oldest leaves turn yellow, but the top of the plant still looks fine, that is usually a symptom of nitrogen deficiency. When nitrogen is deficient in the soil, plants will move nitrogen from the oldest leaves to new leaves, resulting in yellowing, or chlorosis, of the oldest leaves. The Sunset Western Garden Problem Solver recommends using a fertilizer containing nitrogen according to directions on the label for the kind of plant you have. You did not mention what kind of plant it is. The fertilizer will give the plant a quick boost. For longer term health, blood meal or fish meal scratched lightly into soil surface around the plant (follow package directions for amount), topped with a one-inch layer of compost will improve the nitrogen content and overall quality of the soil.

(Adding an inch of compost to planting beds in early spring is a good annual practice for replenishing soil nutrients and keeping plants happy.)

You wondered if too much water could be the problem. Overwatering can produce nitrogen deficiencies in the soil by leaching nitrogen down through the soil and away from plant roots. Different plants have different water requirements. Do you know what kind of plant it is? Without knowing what kind of plant it is, and without seeing it, we can only give possible explanations.

Now back to your first question. There are lots of different patterns of yellowing of leaves and each has a different cause. Is it just the bottom, oldest leaves, or newest leaves, or all leaves, or just the edges of leaves, or just between the veins. I would need to know more before even hazarding a guess. But to get an accurate diagnosis for the problems both of your plants are suffering, we recommend you take samples of each, of good leaves and bad and a little bit of soil from around the root zone of each plant to your local Master Gardener Clinic. You can find a Master Gardener Clinic on the King County Master Gardener website.

Date 2018-04-11
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Plant Answer Line Question

Keywords: Prunus laurocerasus, Fungal diseases of plants, Bacterial diseases of plants

I have some laurel bushes that are developing black or dark brown leaves. It starts at the top and then works down. Trimming them off seems to help but then another bush develops the problem. I want to take care of this before it gets out of control. A neighbor had an entire laurel die--it was probably 15 feet tall.


While I cannot diagnose a plant problem via e-mail, it might be a bacterial or fungal problem, or an environmental disorder. I am assuming your laurels are English laurels (Prunus laurocerasus), not Mountain laurels (Kalmia). According to the Oregon State University Extension's Plant Disease database, English laurel can suffer from leaf spots and shothole. Excerpt:

Cause: Shothole symptoms are commonly observed on Prunus sp. and can be caused by a variety of factors. The bacterium Pseudomonas syringae pv. syringae and several fungi including Cercospora sp., Blumeriella sp., and Wilsonomyces carpophilum (Coryneum blight) can cause leaf spots and shothole on cherry laurel (English laurel, Otto Luyken, or 'Zabeliana'). Copper spray injury and boron toxicity can also cause leaf spotting and shothole. When symptoms are advanced, it is not possible to identify the cause specifically.

Cherry laurels (English laurel, Otto Luyken, or 'Zabeliana'), P. laurocerasus and sometimes other Prunus sp. including cherry and plum, commonly show shothole symptoms resulting from cultural or environmental stress. Research has failed to identify what specific stress is responsible. Both container- and field-grown laurel can develop symptoms.

Symptoms: Necrotic leaf spots with circular to irregular margins. Bacterial spots are brown surrounded by a reddish border with a yellow halo. Abscission layers develop around necrotic leaf spots causing the injured tissue to drop away, leaving holes and tattered areas in the leaf (as if someone fired a shotgun at the leaf-thus the name shothole). After tissues drop, most often it is difficult to determine specifically what caused the initial injury. Observations of early symptom development, signs, and symptoms on other areas of the plant may help make an accurate diagnosis. Note the holes in the leaves.

Cultural control: No management practices have been shown to help reduce physiological shothole. For disease-induced shothole, try the following cultural practices.

  • Avoid overhead irrigation.
  • Remove and destroy fallen leaves.
  • Do not plant near other flowering or fruiting Prunus sp.

If the problem is shothole, this is usually an environmental disorder, and infected parts of the plant should be removed and destroyed.

Here is more information from U.C. Davis Integrated Pest Management on bacterial blight, which in laurels usually affects only the leaves.

If you want to be sure of what the problem is, I suggest bringing samples of the affected leaves to one of the Master Gardener Clinics in our area.

Date 2018-06-27
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Plant Answer Line Question

Keywords: Prunus laurocerasus, Pruning shrubs, Hedges

We have inherited a 25-foot tall English laurel hedge. The former owner never took care of of so most of the 'inside' is just dead branches, but the rest is VERY healthy. Our neighbors would like us to prune it so it's not obstructing their view, and I'd like to reduce its size so I don't need to climb a ladder to prune it in the future. Can I cut it back severely, and regrow it into a more manageable hedge? I don't have the energy to remove it entirely.


I doubt that anyone would ever consider English laurel (Prunus laurocerasus) a manageable hedge plant since what it really wants is to be a tree, but since you want to keep it as a screen, you should be able to cut it back quite hard. It will most likely put on new growth. However, it will look fairly awful while you are waiting for this to happen. According to local Plant Amnesty pruning expert Cass Turnbull (in her Guide to Pruning, Sasquatch Books, 2006), "radical renovations of laurel hedges are common. In the spring, saw the overgrown hedge into the desired shape, except perhaps a foot or two smaller than the final desired size. That's because it will need that room to resprout and be sheared into a thick green coat again. Be sure to cut your hedge narrow as well as short. It should be narrow enough for one gardener to reach across with a hedge shear. I have only seen one laurel hedge that didn't recover from this radical treatment. (...) Please avoid heavy pruning on a hot July or August day, as you might burn up some internal leaves or scald the bark."

Date 2018-07-12
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May 31 2018 13:14:08