Plant Doctor Archive

Yellowing gardenias

BOTH my Gardenia radicans and Gardenia jasminoides var. veitchii have yellow leaves and no flowers. I've tried fertilising them, but they're still not doing well. They're in a relatively new garden between the house and a new path, with a watering system and bark mulch so they don't dry out. All the other plants in the same garden are doing well. Can you help?

THEY'RE almost certainly suffering from lack of iron. Gardenias are acid-loving plants and if the soil is slightly alkaline they can't take up iron from the soil.

It's quite common for lime seeping from new concrete to affect soil in nearby gardens, raising the pH, so acid-loving plants like gardenias and azaleas are adversely affected.

But there's an easy solution. Simply water your gardenias with a solution of iron sulphate and water - around 150g in half a bucket of water. Give them a good soaking. The change should be quite dramatic. New growth of deep green leaves with flower buds should occur within a few weeks during summer.

You can buy iron sulphate from most garden centres, or use iron chelate fertiliser - there are several brands available - which specifically alleviates iron deficiency in acid-loving plants.

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