Lilies – with valuable reserves of strength in their robust storage bulbs – are naturally healthy. These simple tips will help them thrive for many years:
- Water them while they’re growing if it’s dry
- Make sure they’re never waterlogged, especially when they’re dormant
- Give them plenty of fresh air – as a rule of thumb if there are other lilies nearby their leaves shouldn’t touch, and in the garden they are much happier scattered among other plants than being segregated in a “lily bed”.
Like all plants, they do have enemies, though. These are the main ones:
Lily beetles
From May on, keep a watch for these bright red invaders, the only really serious pest of lilies. They’re easily spotted near the tops of lilies, and easy to catch. A morning patrol is best, while they’re still a bit dozy. Without shaking the plant, carefully hold one cupped hand, a small bowl or a spoon, below the beetle, and pick it off with your other hand (if it drops off, the bowl will catch it – otherwise it falls to the earth, staying upside down, and seems invisible). If it has laid eggs on your lilies, the eventual larvae, covered with their own excrement so that they look like very small dark bird droppings, eat the leaves. Keep a careful eye out for this damage – remove any affected leaves with the larvae, and destroy. The most effective chemical control, imidacloprid, is no longer available in the UK, but pesticide sprays claiming lily beetle action can be helpful. There are signs too that one or two tiny native species of parasitic wasps, getting a taste for the larvae, are becoming a natural ecological control in some areas.
Snails and slugs
can bite out the flower-holding heads of new lily shoots emerging in spring, or even gobble up a whole potful of tender new lily seedlings. Springtime bait is the defence.
Vine weevils
make similar notches in lily leaf edges to those made by adult lily beetles. Their underground larvae, little off-white maggots with brown heads, can kill lilies by eating the roots and bulb base-plates. A torchlight night patrol can pick off the dull-coloured adults, easily silhouetted on leaf edges, and is worth repeating until the coast is clear. If you get a bad infestation, water with a commercial predator nematode such as Nemasys in spring and autumn.
Botrytis
starts as small brown spots on leaves which in humid weather can spread very quickly, killing that and other leaves and ending the growing season too early. Removing affected leaves as soon as spots show is some help, as are fungicidal sprays alternating different types; but keeping each lily clear of its neighbours, with plenty of airflow, is the best prevention. Clear up dead leaves and stems quickly to remove spores of the fungus, which would overwinter.
Virus
Disease usually shows as streaky leaves, distorted leaves and flowers, and perhaps rather stunted growth. It’s usually spread by aphids, so it’s well worth controlling these even though they don’t often damage lilies very badly themselves.