Thorny problems: Is my rhubarb poisonous? Montbretia: friend or foe? Geoff and June Ward have had a fantastic show of montbretia this year and want to know where they can buy more. It is a funny thing, but I have not seen ordinary montbretia (Crocosmia x crocosmiiflora) for sale for years, since it seems to have been superseded in our affections by less invasive, larger-flowered and generally more interesting crocosmia varieties (such as the spectacularly scarlet and lanky 'Lucifer"). Lists of these varieties, with the names of suppliers, take up more than three pages in the RHS Plant Finder (which can be accessed online at rhs.org.uk). So vigorous is old-style montbretia that in certain parts of the country it has escaped from gardens (or was it chucked over hedges?) and now brightens up the August grass verges rather splendidly. Nan Miller also loves this plant and its late blaze of colour, but has a different problem since acquiring some crocosmia three years ago (she doesn't specify the variety). In its first year it flowered rather well, the clump of foliage quickly expanding to take over one corner of her garden - but after that first year it failed to produce a single flower. She has dug up half of the patch and put it in the compost heap. She wonders if the rest should follow. First, the possible reasons for lack of flowers: crocosmia grows from corms. Annually, in addition to producing cormlets (that won't flower for a couple of years), each older corm throws up a new one on top of the previous one. What eventually lies under the ground, therefore, in addition to a mass of developing cormlets, is a series of stacked mature corms, the top one being plump and active. Eventually a crocosmia patch will become congested and lose its vigour. The mature corms will, when dormant, need to be separated and replanted. The top corm of each stack should be retained, along with the best cormlets, while the rest of each old stack should be jettisoned. I have to say that after only three years, Nan's patch is unlikely to be too crowded to flower. In this case, the area could simply be too dry, and possibly shady, the first year's successful flowering in her garden being the result of previous growing conditions and treatment. Whatever Nan decides to do, I should add a rather dour word of warning: getting rid of crocosmia is no mean feat. Disturbed tiny cormlets from former clumps may throw up flowerless shoots for ages. And older crocosmia corms dumped in the compost heap seem to inevitably find their way back into the garden somehow - and they won't flower, either. Rhubarb, rhubarb I have been growing rhubarb for many years, but a friend told me recently that it should not be pulled in or beyond August (something I have probably been doing for years). This is because, she said, the sap is no longer rising and poison from the leaves starts to drain into the stems. Is there any truth in this? We have never appeared to suffer, but with a four-year-old grandson who loves rhubarb and custard, I don't want to take any risks. Barbara Cooper, via email Don't worry; this is an old wives" tale. You should indeed stop pulling rhubarb around July to allow the plant to recover during the remainder of the summer and develop a strong root system to support similar constant pulling the following year. The leaves (which should be cut off as soon as the stems are pulled) are indeed poisonous, containing oxalates (also present in smaller quantities in spinach, potatoes and other veg). But you would have to eat an awful lot of rhubarb leaves to do you serious harm - and who would want to? Rhubarb leaves are, incidentally, a completely harmless addition to the compost heap. My friend Esther also tells me that her hens gobble at them with great relish, with no ill effects.