Expert: Long Island Gardener - 5/15/2008

Question
I transplanted 2 lovely Dahlias into a large pot.  After 3 weeks the leaves are turning white and the blooms are very dull. I bought them from a garden center.  Also noticed that my Hibiscus and Feather blooms appear dull. Everything else is bright and pretty.  What am I doing wrong?  I live in zone 8 and 4 miles from the ocean as the crow flies. Lousy soil, thus am resorting to pots.

Answer
There is a Dahlia disease called 'White Smut', caused by a Fungus called Entyloma dahliae, that appears from time to time.  It attacks the leaves of Dahlias that are overwatered.  Lower leaves go first, infected by splashing Soil and Water on them.  Then it makes its way up the plant.  Leaf drop follows.

Easy to solve.  Don't use Fungicide.  Simply stop getting the leaves wet.  Try bottom-watering with a tray to soak the moisture up instead.  I know you want to keep the Dahlia watered; these are thirsty plants that do not like to be left waiting for water when they need it.  But your willingness to cooperate with this demand has left the Dahlia, so to speak, in hot water.

Pinch plants to encourage side shoots, and don't fertilize -- it will encourage soft new leaf growth that is vulnerable to this problem.  Instead of Fungicide, which destroys all beneficial organisms in the rhizosphere including "'good' Fungi, try a dose of 'Messenger' Harpin Protein.  Clinical trials indicated it was highly effective in building disease resistance, and it does that without any anti-earth chemicals.  In a few short weeks your Dahlias will be good as new, and ready to bloom.

THE LONG ISLAND GARDENER