Plant Doctor Archive

Rhododendron care

I'VE inherited a garden full of rhododendrons. They all flowered wonderfully this year, but I don't know what to do now. Should I break off all the old flowers? And do rhodos need any special fertiliser?

CUT off the old flowers to prevent seed pods forming and to encourage the plant to put energy into new growth which will carry next spring's flowers. You can prune rhododendrons now too, if they're getting big. Old plants can be pruned back severely and will soon regrow. Otherwise just remove any dead or damaged shoots and shape the plant as necessary.

Generally rhododendrons don't need a lot of fertiliser but if they look hungry (pale leaves, perhaps even yellowing leaves, and not much fresh growth) you can feed in spring with a blend specially formulated for acid-loving plants - often sold as azalea, camellia or rhododendron fertiliser.

Rhododendrons have very fine roots that grow close to the soil surface, so they appreciate a mulch of acidic, organic matter like peat or fine bark which keeps the root system cool and conserves soil moisture through the heat of summer. A layer of mulch, 6-8cm deep over the root system (avoid contact with the trunk) can have a greater beneficial effect than an application of fertiliser - but there's no harm in doing both for an extra boost. Make sure to follow the recommended application rate on the fertiliser bag, those fine roots can be damaged if you overdo it. And water the fertiliser in well if it doesn't rain much for the following few days.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.