How to cure yellowing rhododendrons

The way to healthy azaleas, camellias and rhododendrons: glossy green leaves and bountiful blooms

Rhododendrons, azaleas, and camellias are amongst our most spectacular flowering shrubs. However these, and several others, need acid soil to thrive. They will not tolerate alkaline soil conditions: their leaves go yellow, growth is stunted and they eventually fail. When grown on the right soil, or in pots using the right compost they can suffer from yellowing leaves if watered with hard tap water, or just when the right nutrients are exhausted. Is there a solution?

Why can’t these plants grow on alkaline soil?

These plants are unable to access certain plant nutrients, particularly iron, when soil conditions are alkaline. They need iron to thrive; lack of it causes the leaves to yellow, particularly between the veins. Adding just any fertiliser cannot help; these plants are light feeders and need specific slow-release fertilisers and iron that can be easily absorbed.

Which plants are susceptible?

In addition to those already mentioned all ericaceous plants are lime haters. These include pieris, leucothoe, enkianthus, andromeda, calluna, vaccinium (blueberries) and gaultheria. Hydrangeas are not ericaceous, but they can suffer from the same yellowing foliage on alkaline soil, due to iron deficiency. Raspberries are also happiest on acid soil and can display similar foliage discolouration.

The cure?

When lime hating plants start to display yellowing leaves Vitax Seaweed plus Sequestered Iron applied as a drench over the foliage and the ground around the plant will often help to restore the foliage. Seaweed is a growth stimulant and the sequestered iron supplies the nutrient in just the way the plant needs it.

In addition lime hating plants need an annual feed with Vitax Azalea, Rhododendron and Shrub Fertiliser. This is an organic fertiliser which breaks down slowly in the soil releasing all the nutrients your lime hating plants need. Keeping the soil moist when the plants are in growth is essential.

This treatment is ideal after flowering. The plants use a lot of nutrients to produce a spectacular floral display. If you give it a tonic and feed after flowering, new growth will be healthy and vigorous, ready for next year’s flowers.

Does this work on any soil?

Vitax Seaweed plus Sequestered Iron in conjunction with Vitax Azalea, Rhododendron and Shrub Fertiliser will cure the yellowing foliage of rhododendrons on neutral and acidic soils. It will also correct the condition on plants in pots that are suffering from the effects of hard water. Often the supply of essential nutrients is simply exhausted; this tonic and fertiliser will put things right.

However, even regular use will not enable the successful cultivation of lime-hating plants on alkaline soils. In these conditions it is far better to grow lime-hating plants in containers using Ericaceous Compost.

Andy McIndoe for Vitax