[Alice]

I grew two Eucalyptus erythrocorys from seed a few years ago. The trees are now at least 2.5 m high but this year the leaves on the lower branches (below 1.5 m) have started to turn yellow. Is this normal or are they suffering from something?

[Trevor Australis]

Eucalyptus erythrocorys the Red-Cap mallee is a semi-desert plant. It grow where the soils are alkaline, thin red sand over sheet limestone. It resents fertiliser. How do these conditions compare with yours. Too much water or food could be the cause.

[Alice]

Our Eucalyptus erythrocorys receive no fertiliser, just the occasional handful of manure. The soil is alkaline, similar to what you describe, Trevor, but we did improve it when we planted them originally. We water them by drip irrigation once a week from May to September, as we don't normally get any rain during the warmer 6 months of the year. Do your think we should stop or drastically reduce this, considering the size of the trees? By the way, the growing tips look green and healthy and the trees have flowered and set seed.

[Trevor Australis]

if your Euc. erythrocorys is flowering and setting seed you must be doing something right. The tree is obviously happy in your conditions. I think I would be inclined to cut back on the water though. Incidentally, this species is not all that long lived - about 12-15 yrs, by which time it is very ugly  and tends to collapse.