Question from Joan:

Every year my honeysuckle grows full with lots of blooms but after that most of the leaves turn yellow and fall off. Why

Answer from Pat:

Let’s begin with a blanket answer: The first thing that comes to mind with any plant, not just honeysuckle, having yellow leaves that drop off and fall to the ground is lack of nitrogen. The cure is to feed it. Seasonal leaf drop is another thing. Leaves do drop, after all, even from evergreen plants. So that too might be the problem. You might even be growing a honeysuckle that is not well adapted to your climate. In that case, weather extremes can cause leaves to go yellow and drop off. Also, make sure the plant is getting adequate moisture and not too much and adequate nutrition (Nitrogen, phosphorus, potassium and trace minerals.) A product called John and Bob’s Soil Optimizer can provide trace minerals and often gives sick plants a shot in the arm if the problems derive from insufficiency in plant minerals or bio-organisms. Additionally, if the ground is too wet or too dry, either of these things can lead to yellow leaves that drop off. (I will discuss this in more detail below.

Now to your specific question regarding honeysuckle: there are at least 200 honeysuckle species and even more if you count all the named varieties. About 20 species and varieties are commonly grown in the Western states of the United States of America. All are members of the Lonicera (honeysuckle) genus. Some are shrubs, some are climbers, and some come close to being trees. They are adapted to a wide variety of climates, ranging from those that are adapted to living in Siberia to those that would be happiest in a steamy tropical jungle. At least one type bears edible berries. Additionally, people often write to me with questions about Cape honeysuckle (Tecoma capensis) that is not a honeysuckle at all. (If this is what you are growing, please see the other sections in this blog on that subject.) Thus, you can see that without telling me where you live or which honeysuckle species you are growing or whether it’s in a container or the ground, it’s virtually impossible for me to give you a specific answer. That said, I will hazard a guess or several guesses on what might be the problem and you will have to figure it out and take your pick.

S now let’s discuss some possibilities. First, I should tell you that honeysuckles are usually easy to grow and have few problems. In Southern California where I live, common or Japanese honeysuckle (Lonicera japonica) is an invasive ground cover plant whose seeds are spread by birds. Seldom is there a problem with leaves falling off. Almost nothing ever goes wrong with it and that combined with its vigor and invasiveness makes it a terrible pest. Fertilizing it is a bad idea since it will become even more bad mannered than it already is. (I hasten to say this since I am going to mention fertilizer below, but I would not normally recommend you use it if you are dealing with a bank covered with honeysuckle in Southern California.)

There is another honeysuckle, however, that is a tropical type, the giant Burmese honeysuckle (Lonicera hildebrandiana). This is a vigorous, fast- growing vine that in time can grow a thick woody trunk and cover a very large structure. (Perhaps this is what you have?) The leaves of this plant are evergreen and quite large and so are the flowers. The leaves often go bright yellow and fall off year round. If giant Burmese honeysuckle is flowering and then goes dry, the leaves are likely to turn bright yellow and fall off. If stressed by heavy bloom, it may drop all its leaves after bloom and then grow new ones. If it doesn’t have enough nitrogen the new leaves will be too small. The solution is to fertilize with ample balance fertilizer and keep the plant well watered so that it can quickly grow leaves to replace those that naturally fall. (You cannot stop them from falling; it’s the nature of the plant, but good cultural practices will stop them from falling off all at once.) In short, Burmese honeysuckle is not a drought-resistant plant. It needs lots of water. Keep it well-fed, well-watered, and well-mulched. Train it on a trellis or arbor, and prune it to encourage branching and to keep it in bounds. It is not an appropriate plant for pot culture.

With any plant, including honeysuckle, leaf drop after massive bloom might occur it it’s growing in soil with ample quantities of phosphorus and potassium and insufficient nitrogen. Also, if a plant is doing well in winter at lower temperatures, then the weather warms up and the soil is too wet, root rot can set in. This can cause yellow leaves that drop off. (Usually, however, this is fatal and you tell me this happens every year. Thus I don’t think root rot is your problem.) It is true that wet soils combined with lack of nitrogen can cause leaves to go yellow and fall off which can be a sign of root rot and wet soils, but leaf drop can also occur from transplant shock or even from soil suddenly going too dry. For example, a frequent garden scenario, in Mediterranean climates is that plants do fine in the rains of winter, then dry weather hits, and the plant has insufficient nitrogen to keep growing so the leaves go yellow from lack of nitrogen and fall off from drought. Sometimes plants flower massively and put on a lot of fruit when they think they are going to die. They want to make sure they at least leave a few babies behind to take their place after their own tragic demise.

Here’s an example: I once was called in by an elderly neighbor to look at her Meyer lemon that had been growing fine for several years in a half-barrel. Then suddenly without warning all the leaves fell off but the tree still had loads of flowers and even many little fruits—more than usual my neighbor said. She was afraid the tree had died and was convinced a disease or pest had done it in. Her gardener wanted to spray it with Malathion. I said, “Whatever you do, don’t let him do that! I’ll come right over!” Knowing him well, a dashed over there right away and my neighbor showed the tree to me. It was alive, that was obvious. Its twigs and tip wood were still bright green and when I pushed my thumb nail in them sap came out, and there was not a pest in sight. Any pests, if there were any, had dropped off with the leaves. My neighbor said her gardener was watering the tree twice or three times a week. (He was standing right there sprayer in hand, staring at the tree and at me.) I took one look and saw the whole container was chock full of roots—no soil at all—, and there was a space about half an inch wide all around the inside edge of the half-barrel where the water flowed right away with none of it ever reaching the plant.

I told the gardener to bring the hose and pour water onto the roots. Both my neighbor and her gardener could see when he did that the water flowed right off the roots and out the bottom of the tub and not one drop was penetrating the roots. I shoved a trowel into the root ball to show them the roots were dry as a bone. The tree had dropped its leaves to try to save its own life. In more scientific terms, it wanted to prevent loss through transpiration of the last little bit of moisture it still contained. You might have a situation like this with your honey suckle if it’s growing on a bank so all the irrigation water is running away instead of getting to the roots. Or the same thing might be happening in a pot, if that’s how you’re growing it. In the case of the Meyer lemon tree, I told the lady to have her gardener dig a hole in the ground and take the tree out of the tub, loosen up its roots, and plant it in the ground, then build a watering basin around it and keep it watered. He put the sprayer away and began digging a hole. After it was planted in the ground and had leafed out I told her to feed it. Her gardener did all this. The little tree breathed a sigh of relief, drank in the water, and almost immediately sprouted new leaves.

After reading all these possibilities I suggest you first read up on honeysuckles to find out which one you have, then dig into the soil where it grows and find out if the soil is too wet or too dry. If too dry, fertilize, water, and mulch the ground to encourage growth. If too wet, reduce irrigation. If your plant is in clay soil that is compacted due to alkalinity, spread gypsum to increase drainage. Add mulch to improve the soil. If you have never fertilized, begin fertilizing and from now on prune after bloom to encourage re-growth. Also from now on (except in the case mentioned in paragraph one above) fertilize at regular intervals at least once a year early in the growing season with an all-purpose organic fertilizer to provide adequate nitrogen for growth. Chicken manure should work well. Apply to the ground, cover with mulch, and water it in.