Question:

In July I planted Suttons Lupin Gallery mix seeds in a cold greenhouse in John Innes fine seed compost and 17 seeds germinated in a seed tray. I transplanted them to three-inch pots and all grew healthily. When large enough I again transplanted them into eight-inch pots to grow on for spring planting, in West's compost mixed with 50pc of my own garden compost. Within two or three weeks the plants were badly attacked leaves all eaten. They were treated with PY insect killer spray but this had no effect. I then sprayed with Provado Ultimate Bug Killer which has had no effect. Can you please advise me? (RA Harris, Sprowston Green)

Answer:

The problem with your lupins is one of those very complex conundrums that starts with the compost. Although the compost you have used may be very suitable for some things, whenever you mix your own ingredients you bring in lots of variables and I think you may have either over- or under-fed your lupins causing them to be vulnerable to pests.

The leaf damage was almost certainly caused by slugs that may have come in with your compost. Slugs and snails love lupins, and the sprays you have used will have little or no effect on them.

The sample you sent in does have some aphids on it so they will also weaken the plant although not to the point that they will cause the amount of damage you are seeing.

Lupins have their own type of aphid first detected in Britain in 1981; the lupin aphid is now widespread throughout Britain. Lupin aphid is a member of the greenfly and blackfly family. It is a sap-sucking insect that feeds on lupins (Lupinus). Keep an eye out for large, greyish-white aphids, up to 4mm long, form dense colonies on the underside of leaves and on the flower spikes of lupins. Lupin aphid is present all year round, small numbers of aphids overwinter on the basal buds and they begin to increase in number in spring.

Although most plants will germinate quickly in a greenhouse and benefit from the additional heat provided, some outdoor perennials do not like to get to hot, this will slow their growth and can kill them. Move your lupin outside and if possible plant them in their flowering position and they should survive much better.

You may want to start again next spring with a new packet of seeds and stick with the John Innes compost and move the plants outside as soon as they are established.

•This article was first published on October 1, 2011.