Gadenin日本語Get the appFlowering comes in flushes, and the gaps are normal
Verbena does not flower evenly the way some bedding plants do. It opens a wave of flat flower heads, holds them for a week to ten days, lets them fade, and then spends two or three weeks building the next wave on new shoots. A plant with almost no open flowers for a fortnight in the middle of summer is not failing; it is between flushes, and the shoots it is making now carry the next set.
The practical consequence is that you should judge a verbena over six weeks, not over one. If in six weeks you have had two clear waves of flower, the plant is doing what it does. If you have had one thin wave and then nothing but leaf, something is genuinely wrong, and the sections below cover the three causes worth checking in order.
Too much nitrogen is the most common cause
Verbena flowers hardest when it is slightly hungry. Rich compost, a fresh dose of general purpose fertilizer, or a spring feed intended for the lawn drifting into the bed will all push it into leaf. The signature is unmistakable once you know it: large soft dark green leaves, long spaces between the leaf joints, a plant that looks healthy and vigorous, and almost no flower heads.
The correction is to stop, not to switch products. Give it nothing for four weeks, shear the plant back by a third to take off the soft growth, and let it rebuild on what is in the soil. Flowering usually resumes within a month. In containers, where you cannot simply wait for the nutrients to run out, flush the pot through with plain water two or three times to wash the excess out of the compost, then resume feeding at half strength only once flowering has returned.
| What you see | Most likely cause | What to do |
|---|---|---|
| Lush leaf, long stems, very few heads | Too much nitrogen | Stop feeding for four weeks and shear back by a third |
| Compact plant, small pale leaves, few heads | Underfed in a container | Half strength high potassium feed every two weeks |
| Flowers only on the sunny side | Uneven light | Turn the container a quarter turn every few days |
| Whole plant flowering less as summer peaks | Heat above 90F (32C) | Wait; flowering resumes as nights cool, keep watering steady |
| Bare middle, flowers only at the tips | Plant has outgrown light shearing | Cut back hard by a third, all over |
| Gray dust on leaves and flowering stalled | Powdery mildew | Improve spacing and airflow, remove worst foliage |
Sun and heat set the ceiling
Below six hours of direct sun verbena will not flower properly no matter how well you treat it in every other respect. This is the one variable you cannot compensate for. A plant on a wall that gets morning sun and then goes into shade at noon will make plenty of foliage and a thin scatter of heads, and moving it is the only real fix.
Heat works differently. Verbena flowers best between about 70F and 85F (21C and 29C). Above roughly 95F (35C) it keeps its leaves but slows bud production sharply, and the heads that do open are smaller and fade faster. That midsummer lull is temporary and passes as the nights cool. Do not respond to it by feeding harder, which only pushes leaf; keep watering steady, keep the plant shaded from the very worst of the afternoon if you can move it, and wait.
A verbena that flowered well in early summer and then stopped in the hottest weeks will almost always come back strongly in early autumn, often with the best flush of the whole year. Do not pull it out in the lull.
By midsummer, light shearing stops being enough
There is a point most trailing verbena reaches partway through summer where the center of the plant has gone bare and woody, and all the flowering has migrated to the last few inches of each trailing stem. At that stage taking an inch off the tips achieves nothing, because you are trimming the only part still producing.
The answer is a proper cut back: reduce the whole plant by about a third, cutting into the leafy part of the stems rather than into bare wood, and accept two to three weeks with very little to look at. New shoots break from the leaf joints along the shortened stems, the bare middle fills in, and the plant carries a full flush again into autumn. Done in the first half of summer this reliably buys a second half of the season; left until the weather is already cooling, the plant may not have time to rebuild.
Record when the flushes came
Write down the date each flush opened and the date you sheared. After one season you will see your own plant rhythm: the number of weeks between shearing and the next wave, which is usually two to three but varies with your climate and light. After two seasons you can plan around it, timing a shear so a full flush lands when you want the display at its best.
It is also worth noting which plants ran to leaf and how much you had fed them. That is the fastest way to find the feeding level your own soil actually needs, which is very often less than any label suggests.