Plant Doctor Archive

Ailing junipers

I have some junipers, both as bonsai and as potplants. A number of them are showing some serious dieback for unexplained reasons. They get watered properly, yet branches slowly go a dull colour and die off. Light feeding doesn't help either. Is there a soil disease that might cause this and how would I treat it?

Has this plant just started showing signs of dieback or has it been gradual? Junipers do not like hot, humid weather, so if you live in Auckland, that could be (part of) the problem. It is also possible the plant could be affected by a root disorder such as Phytophthora. The most common cause of this is plants going through a period of drought and then being watered.

Cut back the infected foliage and dispose of it in the rubbish bin or burn it to stop the disease spreading.

There is a spray to control root disorders called Ridomil — but I do not know of it being available in small quantities for the home gardener.

Once the plant is infected, there isn't a lot that can be done, other than cutting it back and hoping it recovers.

Junipers do not need regular feeding. Feed in spring with a controlled release fertiliser such as Osmocote. A quality potting mix will have enough fertiliser in it to feed the plant for up to three months, then feed again the following spring. An occasional liquid feed with Nitrosol will benefit the plant.

Junipers require full sun and a well-drained potting mix or soil.

I would suggest a sample of the dieback be taken to your local garden centre for identification — they should be able to assist in identifying the problem.

Advice by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor of Resource Management.

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