Weekend work: Time to plant dahlias

What to do

Plant dahlias, covering the tubers with about 7cm of soil. The bronze-leaved varieties are showy, but all dahlias are difficult to work into the average flower border. They leave large holes until midsummer and then overcompensate by crowding out their neighbours.

Prune osmanthus to shape after it has flowered. They make very attractive domes if you cut back over-ambitious leaders at this time of year. Aim for a well-balanced, roughly rounded shape.

Wise gardeners will stake herbaceous perennials soon, before they actually need it.

Keep sedums compact by cutting back the first shoots and forcing them to re-sprout, or by winding a web of soft string round them, attached to a short stockade of sticks set round each clump.

Continue to deadhead daffodils, leaving stems and leaves intact. This will force them to concentrate on building up next year's bulb.

Attack bindweed, which is already curling its hideous way through clematis and roses. Pull groundsel before it seeds. Heave out creeping buttercup, a pretty weed but a bully.

What to see

250 exhibitors will be gathering next weekend in the gorgeous park at Courson, south of Paris, for the well-established party that is Les Journées des Plantes. Take the Eurostar to Paris and make for the station of Massy-Palaiseau. Free shuttles run from the station to the show; 17 May (12-7pm) and 18-19 May (10am-7pm), admission €17, domaine-de-courson.fr