Why did my plant suddenly collapse and die?

There is a real difference between decline and collapse. A plant that faded over a month has a cultural problem. A plant that was fine on Sunday and lying flat on Wednesday has had something cut through — its roots, its stem base, or the vessels inside it — and that is a much shorter list to work through.

Step by step

1. Pull gently on the plant.A plant that lifts out of the soil or compost with almost no roots at all has had them eaten, and in a container that means vine weevil grubs. Look in the compost for fat, creamy, C-shaped grubs with brown heads.
2. Look at the stem where it meets the soil.Soft, black, sunken tissue right round the stem means the plant has been girdled at the collar by basal rot, and everything above it is cut off. Clear the soil back and check the whole circumference.
3. Check for a severed stem.A young plant lying on its side with a chewed stem at ground level is cutworm or slug damage. A woody plant with a ring of bark missing around the base has been ring-barked by rabbits, deer, voles or a strimmer, and once the ring is complete nothing above it can survive.
4. Check the compost for a nest or a void.An ant nest in a pot fills the rootball with air tunnels so water runs straight through, and a plant can collapse abruptly in hot weather as a result. Soak the pot in a tray of water and see what emerges.
5. Consider whether it simply dried out.A pot that dried right through in a hot spell collapses fast and looks dramatic. Lift it — a bone-dry rootball is startlingly light. A thorough soak from below within a few hours often brings it back.
6. Cut a stem across and look inside for vascular wilt.Fusarium and verticillium wilts block the water-conducting vessels inside the stem, which shows as a brown or dark ring or streaks in the cut surface just under the bark. Wilting often starts on one side or one branch. Both live in the soil, both persist, and neither can be treated — the plant goes, and susceptible species should not be replanted in that spot.
7. Check clematis specifically.A clematis that wilts from the top down, suddenly, in early summer is the classic case of clematis wilt. The plant usually survives if it was planted deep — cut the affected stems right down to ground level and it reshoots from below the soil.
8. Look for honey fungus on woody plants.Several woody plants dying in the same area over a few years, sudden collapse in full leaf, creamy-white sheets of fungal growth under the bark at the base smelling strongly of mushroom, and flat black bootlace strands in the soil. This changes the whole plan for that part of the garden.
9. Consider heat and root temperature in containers.A dark pot in full sun on a paved surface can reach temperatures that kill roots outright, and the plant collapses within a day or two. Move pots off hot paving, shade the pots rather than the plants, and use light-coloured or larger containers in a sunny spot.
10. Decide what to do with the space.For rot, grubs, drought and mechanical damage, replanting the same thing after correcting the cause is fine. For vascular wilt, clubroot, white rot or honey fungus, the ground is committed for years and the answer is a different, unaffected plant or a container.

Tips

• Photograph a collapsed plant before removing it, including the stem base and the roots. If it happens again in the same spot you will want the comparison.
• A plant that collapses in full flower or with a heavy crop is often one whose roots were already marginal — flowering and fruiting are the peak demand.
• Do not compost a plant that collapsed from an unidentified cause. Green waste is the safe destination.
• In a heatwave, water containers early in the morning and move vulnerable ones into shade. Sudden collapse in July is very often simply heat and drought in a pot.

Common mistakes

• Watering a collapsed plant without checking anything — Half the causes are wet-related and adding water makes them worse. Lift it, look at the roots and the stem base first — it takes a minute.
• Replanting the same thing immediately — If the cause was soil-borne, the replacement follows. Identify first, then choose.
• Assuming a woody plant that collapsed in leaf was struck by disease from outside — Sudden collapse in full leaf on a shrub or tree is the classic honey fungus presentation, and it needs checking under the bark at the base.

If it doesn't work

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