Gadenin日本語Get the appRoot and crown rot is the main killer
The classic pattern is a plant that looks fine in autumn and, by spring, has one or more whole branches that are gray, brittle and leafless while the rest looks normal. That is not frost; it is rot at the base of those stems, caused by water sitting around the crown. Over the following season the dead sections spread and the plant collapses.
Confirm it by scraping the bark at the base of a dead branch with a thumbnail. Healthy wood is pale green just under the surface; rotted wood is brown, sometimes soft, and often smells sour. Cut the dead branch out cleanly back to live wood or right to the base, clear everything from around the crown, and improve drainage. On heavy soil the real fix is lifting the plant onto a raised, gritty bed, and that has to be done at the start of a growing season.
There is no spray for this. Fungicides do not fix a drainage problem. If the crown itself is soft all the way round, the plant is finished; take cuttings from any healthy tips immediately and replace it in a better position.
Tell winter damage from rot
Winter cold damages the outer and upper growth first, so frost-injured plants show browning at the tips and on the windward side while the center and base stay green. Rot works the opposite way, killing whole stems from the ground up regardless of their position on the plant.
Wait until new growth starts in spring before deciding. Lavender that looks dead in late winter often breaks from the lower leafy growth once it warms up, and cutting in a panic removes the wood the new shoots would have come from. Once you can see where growth is emerging, trim off dead tips down to just above the highest live leaves, and no further.
| Symptom | Most likely cause | What to do |
|---|---|---|
| Whole branch gray and dead in spring, rest green | Crown or root rot from winter wet | Cut the branch out, clear the crown, improve drainage |
| Brown tips on the outside and top only | Frost or wind damage | Wait for new growth, then trim to just above live leaves |
| Soft, dark, floppy growth with few flowers | Too much feed, water or shade | Stop feeding, open up light and air, shape at the normal time |
| Fine pale mottling on leaves in hot dry spells | Sap-sucking mites or leafhoppers | Usually cosmetic; a hard spray of water and better airflow is enough |
| Frothy white blobs on stems in early summer | Spittlebug nymphs | Harmless to an established plant; wash off or ignore |
| Ragged holes in leaves and flower stalks | Leaf-eating beetles or caterpillars | Pick off by hand; damage is rarely enough to matter |
| Whole plant yellowing and slowly dying, no rot at base | Soil too acid or too rich | Test pH, lime if below 6.5, stop all feeding |
Sudden die-back of scattered shoots
Occasionally a plant loses individual shoots here and there through the season, each wilting and then browning while the rest of the plant grows normally. This is a fungal die-back that gets in through wounds, and it is worst on plants that are already weak from wet feet, crowding or a badly timed hard cut.
Cut affected shoots out well below the damage into clearly healthy wood, and clean your blade between cuts with a wipe. Take the prunings away and do not compost them near the plant. Then deal with the underlying stress: open up the airflow, stop overhead watering, and make sure the late summer shaping cut happens early enough for the cuts to heal in warm weather.
- Cut in dry weather Pruning wounds made in wet conditions are the entry point for die-back. Do all cutting on a dry day and, ideally, with a dry spell forecast.
- Clean the blade Wipe shears between plants when you are cutting out diseased material. It takes seconds and prevents spreading a problem down a whole hedge.
- Remove the prunings Infected stems left lying under the plant keep the base damp and hold the fungus close to fresh wounds. Take them away entirely.
Insects rarely need action
Lavender's oils make it unattractive to most pests, and the plant is one of the strongest nectar sources in a summer garden, so it is usually full of bees and hoverflies. Blanket spraying does far more harm than the pests would. In practice the only insects you will see in numbers are spittlebugs, whose frothy blobs on the stems look alarming and do essentially nothing, and occasional leaf-eating beetles which can be picked off by hand.
In a greenhouse or a crowded, shaded position the picture changes, and you may get gray mold on damp foliage or aphids on soft growth. Both are symptoms of the same underlying problem: not enough light and air. Move the plant, thin its neighbors, and the pests go with the damp.
Record deaths, not just successes
When a branch or a whole plant dies, note the date, which plant it was, where it sat in the bed and what the winter had been like. Rot is a position problem, and positions repeat: the same corner of the same bed will kill lavender every few years until you either raise it or plant something else there.
A note of the first frothy spittle, the first beetle damage and the first dead branch each season builds into the only genuinely useful diagnostic you have. Two years of records will tell you whether your losses follow cold winters or wet ones, and those two problems have completely different solutions.