Dear Orchid Doc:

I have some Dendrobiums outside, and since the rainy weather I have noticed something looking like soot on them. What’s causing this, and what should I do?

— Merville

Dear Merville

This soot did not just happen; it has been building up for some time.

Sooty mould is actually the excretion of sucking insects called aphids.

Aphids usually multiply during the dry season. Like humans, plants are susceptible to disease (fungus) when they are not watered or fed properly.

As you don’t seem to have a great many orchids, I am suggesting you use some dishwashing liquid with a little cooking oil and wipe the leaves (the way they grow).

Sooty mould might not kill the plants right away, but leaving them untreated will prevent them from breathing properly, or from absorbing the chemicals. After a while, if left untreated, the mould will in fact start to affect the blooms.

If you wish to use a fungicide, you will need to also use an insecticide to get rid of the insects that bring the sooty mould. The most effective fungicide has copper, but in the sun the copper will burn the orchids. Therefore, you would need to protect them from direct sunshine. CHAMPION and Caprid will work wonders.

This you will need to apply once per week for four to six weeks.

Dear Orchid Doc:

I received an orchid as a gift for my birthday recently. It has a tag with the name Epidendrum. As I know nothing about orchids, can you give me any info as to the care?

— Wain

Dear Wain,

Epidendrum orchids prefer the cooler areas of your garden.

They like a lot of water and fertiliser.

Most of them do not like soil. Whenever they are planted in soil they tend to ‘walk out’. Please try a mixture of charcoal, tree fern bark and pebbles.

Always have Osmocote at the root (a time- release fertiliser).

They will reward you during the cooler months , usually from October to spring.

Good luck!