Snake Plant Problems: Root Rot, Mealybugs, Thrips and Cold Damage

The five things that actually go wrong

A snake plant has a very short list of problems, and four of the five on it are caused by the grower rather than by anything arriving from outside. Learning to name the problem quickly matters more here than with most plants, because root rot moves fast and everything else moves slowly.

Work through this table before you do anything. The single most useful diagnostic is to push a finger into the compost, because damp compost and dry compost point at completely different answers.

Root rot: the one that kills

Root rot is not a disease you catch, it is what happens when the roots sit in wet compost with no oxygen. Cold makes it far worse, which is why most losses happen in late autumn and winter rather than in summer.

The symptom people notice is a leaf that has gone soft, slightly translucent and brown at the base, and then simply falls out of the pot when touched. By that stage the rot is already in the rhizome, so act the same day.

1. Pull the affected leaf out Take hold of the soft leaf near the base and pull it straight out. It should come away easily. Smell the base: a sour, sewage-like smell confirms rot rather than ordinary ageing.
2. Take the whole plant out of the pot Tip the plant out and crumble the compost off the roots by hand. Healthy roots are firm, thick and pale orange or white. Rotted ones are brown, hollow and slide apart between your fingers.
3. Cut back to firm white tissue With clean pruners, cut off every soft root and slice into the rhizome until the cut face is uniformly white and firm. Any brown streak left in it will carry on rotting after you replant.
4. Dry the cut surfaces for two or three days Leave the plant bare on newspaper in bright shade with air moving until the cut faces are dry and corky to the touch. This step is not optional and cannot be shortened.
5. Replant dry, and do not water Pot into fresh, gritty potting mix in a pot no bigger than it needs and leave it completely dry for ten days. Then water once, thoroughly, and go back to the normal long intervals.

Never reuse the old compost and wash the pot before it goes back into service. The organisms that finish off a rotting rhizome are already living in that compost.

Mealybugs and thrips

These are the only two insects that reliably find a snake plant indoors, and both hide rather than sit out in the open. Wiping the leaves once a month with a dry cloth is as much a monthly inspection as it is cleaning, and it is how most people catch them early.

Scale turns up occasionally too, as small brown limpet-like bumps along a leaf. Treat it as you would mealybugs: scrape them off first, then follow up.

Cold damage and leaf spot

Cold damage is unmistakable once you have seen it: a soft, water-soaked, almost transparent patch appears in the middle or lower part of a leaf a day or two after a cold night, and it later dries to a papery brown scar. The damage is permanent, so the marked leaf will never recover its appearance.

Leaf spot is far less common and only appears where water sits on the foliage. Small brown spots with a slightly paler halo spread slowly outward, usually on plants that are misted, stood in rain, or crammed against other plants with no air movement.

1. Move a cold-damaged plant, then leave it alone Get it above 50F (10C) and stop watering completely. Do not cut anything for a fortnight, because a soft patch that dries into a firm scar is finished and a leaf you cut in a panic is one you cannot get back.
2. Remove a leaf only if the damage reaches the base Damage in the middle of a leaf is cosmetic. Damage that runs down into the leaf base, or that stays soft and wet after a week, will turn into rot: pull that leaf out cleanly at the base.
3. For leaf spot, fix the air before the fungus Cut off badly spotted leaves at the base, stop wetting the foliage, and give the plant space so air moves around it. Spacing and dry leaves stop leaf spot more reliably than any spray.

A brown, dry tip on an otherwise healthy leaf is usually a heating draft rather than disease. Trim the dead part just inside the brown, leaving a hairline of it, and move the plant out of the airflow.

When a plant is past saving

There is a point at which cutting further does more harm than good, and knowing it saves you weeks of nursing something that will not come back. The test is simple: is there any firm, white, undamaged rhizome left with at least one healthy leaf attached to it?

If there is, cut everything else away and treat it as a small plant. If there is not, the plant is gone, but a single undamaged leaf can still be cut into sections and rooted, so you rarely have to lose the plant entirely.

What to write down

Snake plant problems repeat on an annual cycle, and a couple of lines in a record turn that repetition into something you can act on before the damage starts.

Note the date you last watered before a problem appeared, the room the plant was standing in, and the date you first saw the symptom. After one year you will be able to see whether your rot always follows the same late-autumn watering, and whether your mealybugs always arrive after the plants come in from outside.

1. Log the last watering date before any symptom For rot, the useful number is how many days of damp compost preceded the first soft leaf. Two seasons of that figure tell you exactly how far to stretch your own intervals.
2. Log the first date you saw a pest Mealybugs and thrips return at roughly the same point each year. Knowing that date means you inspect a fortnight earlier next year and catch them while they are still on one leaf.