Gadenin日本語Get the appRot at the base is the failure that kills plants
A celosia that wilts on a hot day and does not recover by morning, with a stem that is soft, dark and pinched right at soil level, has stem rot. This is the one celosia problem that reliably kills, and it is caused by wet soil, cool weather or organic matter piled against the stem. Once the stem is girdled there is no treatment. Pull the plant, take it out of the bed, and look at what made that spot wet.
The seedling version is damping off. A tray of celosia that germinated well and then collapsed overnight, each seedling flopped over with a thread thin brown base, has been kept too wet, too cool or too crowded under a lid. Sowing thinly, taking the cover off at emergence and giving the tray real warmth prevents almost all of it. Watering seedlings from below with clean water rather than splashing from above helps too.
In the ground, the fixes are all about drainage and airflow. Plant slightly proud rather than into a dip, keep mulch pulled back an inch from the stem, water the soil rather than the plant, and space at the distances the form actually needs. A bed that rots one celosia will rot the next one planted in the same spot, so move them if you can.
If several plants in one part of the bed rot in the same week, dig a hole a spade deep there after the next heavy rain and see how long it holds water. That corner needs raising, opening up with grit, or a different crop next year.
Leaf trouble: spots, mildew and mites look different
Brown or reddish spots on the lower leaves that spread upward in wet weather are fungal leaf spot. It needs wet foliage to spread, so switching to watering only the ground stops most of it. Pick the marked leaves off and take them out of the garden rather than dropping them, because the spores overwinter perfectly well on debris lying under the plant.
A white floury dusting on the upper leaf surfaces in late summer is powdery mildew, which comes with warm days, cool nights and heavy dew. It rarely kills celosia but it strips the lower leaves and shrinks the heads. Spacing and airflow beat any spray here: plants at 18 in (45 cm) will show it weeks later than the same plants at 8 in (20 cm).
Fine pale stippling on the upper leaf surface that turns bronze, with faint webbing in the leaf joints, is spider mite, and it is a hot dry weather problem rather than a wet one. Celosia against a warm wall or in a container is prime territory. Hosing the undersides of the leaves hard twice a week breaks the cycle if you catch it at the stippling stage. Once webbing is obvious the plant is usually past saving.
| Symptom | Likely cause | First response |
|---|---|---|
| Stem soft and dark at soil level, plant wilts and stays down | Stem rot from wet soil or mulch against the stem | Pull and remove the plant, improve drainage, pull mulch back |
| Seedlings collapse overnight with thread thin brown bases | Damping off in cold, wet, crowded conditions | Discard the tray, sow thinner, warmer, and uncover at emergence |
| Brown or reddish spots spreading up from the lower leaves | Fungal leaf spot spread by wet foliage | Remove marked leaves from the garden, water the soil only |
| White floury dusting on upper leaf surfaces | Powdery mildew in late summer dew | Strip affected leaves, widen spacing, stop overhead watering |
| Pale stippling turning bronze, fine webbing in leaf joints | Spider mite in hot dry weather | Hose leaf undersides hard twice a week, starting early |
| Head browning from the center after rain | Water trapped in a dense plume or comb | Cut the head off to a leaf joint, water the base from now on |
| Plant stunted, flowers at a few inches tall | A growth check from cold, dryness or a cramped pot | Not a disease. Pinch the head, feed, and sow later next year |
The insects worth watching
Aphids gather on the soft growing tips and around developing heads, distorting them as they expand and leaving sticky honeydew that goes sooty black. On celosia they matter more than the feeding damage suggests, because a head that develops while covered in aphids is misshapen for good. Squash the first colonies between finger and thumb and hose the tips hard, and hoverfly larvae usually finish the job.
Slugs and snails take out young celosia at ground level overnight, and because you plant out small this is the moment of greatest risk. Check with a torch after dark for the first week after planting, clear damp cover from around the stems, and plant a couple of spares so losing one is not a gap in the row.
Leaf miners tunnel pale winding tracks through the leaves, which looks alarming but rarely costs the plant anything. Pick off the worst leaves and ignore the rest. Caterpillars chewing ragged holes in the foliage or into a developing head are worth hand picking in the evening, because a head with a caterpillar inside it will not come good.
| Pest | What you see | What works |
|---|---|---|
| Aphids | Clusters on tips and buds, sticky honeydew, misshapen heads | Squash by hand early, hose the tips, leave predators to finish |
| Spider mites | Stippling and bronzing in hot dry spells, faint webbing | Hose leaf undersides hard twice a week from first stippling |
| Slugs and snails | Young plants gone at ground level, silver trails | Torch check after dark for the first week, clear damp cover |
| Leaf miners | Pale winding tunnels inside the leaf tissue | Pick off the worst leaves. Rarely worth any further action |
| Caterpillars | Ragged holes in leaves or damage inside a developing head | Hand pick in the evening, check inside affected heads |
| Root knot nematodes | Stunted plants, swollen knobbly roots when lifted | Do not replant celosia in that ground, rotate to something else |
Keep a note of which pest turned up and roughly when, along with where in the bed it started. Mildew and mite both begin in the same corner year after year, usually the stillest or the hottest, and knowing that lets you space that corner differently next season.
Knowing when to give up on a plant
Celosia is cheap to raise and grows fast in warmth, so the calculation is different from a shrub. A plant with rot at the base, a plant that has been stunted since it was four inches tall, or a plant fully webbed with spider mite is not worth the weeks of nursing it will take. Pull it, take it out of the garden, and if there is still time in the season sow or plant a replacement into that gap.
The plants worth saving are those with a healthy stem base and a problem confined to the leaves or a single head. Strip the affected foliage, cut the damaged head back to a leaf joint, water the ground and feed lightly, and a celosia in warm weather will push new growth within a fortnight.
At the end of the year, clear the bed rather than composting the plants in place. Leaf spot and mildew both carry over on debris left lying on the soil, and celosia stems are woody enough that they sit there most of the winter holding spores. Pull the plants once frost has killed them and take the material away.