Midsummer plant stress

Friday, July 29, 2011

A weird summer weather pattern has landscape plants really feeling the heat in gardens near the coast, where rain has been irregular and sparse.

For orchid lovers, be sure to water your vandas twice a day, using a light mist in mid-afternoon if it’s not raining. Fertilize weekly, adding extra potassium and magnesium sulfate or Epsom salt (1 teaspoon each per gallon of water) to improve cell health.

At the 5th symposium of the Coalition for Orchid Species held recently at Fairchild, Hawaiian grower Roy Tokunaga emphasized the need of orchids for calcium as the real blossom boosting mineral element. He highly recommended 15-5-15 every week during the summer, “unless plants are under stress, it’s raining or humidity is very high. Then the calcium requirement doubles or triples at these times.” Which means you could be applying the 15-5-15 fertilizer twice a week now for superior plants and flowering. (If doing so, you can skip the addition of Epsom salts and potassium.)

Broad yellow bands on lower
fronds of this Phoenix palms are
signs of magnesium deficiency.

For heat stress generally, you can spray the foliage of your palms and other plants with 1 to 2 tablespoons each Epsom salt and potassium per gallon of water.

Magnesium deficiency is apparent in many Canary Island date palms around South Florida. Look for the yellow bands along the edges of the lower fronds. This is a telltale sign that you’re not using palm special fertilizer (8-2-12) containing extra potassium and magnesium.

The Institute for Food and Agriculture Services of the University of Florida recommends using kieserite four to six times a year on severely affected Phoenix palms. Kieserite is a soluble form of magnesium. The application rate is 2 to 5 pounds per large tree, 4 to 6 times a year for two years. Scatter the product under the canopy.

Regular palm fertilizer should be applied at a rate of 1½ pounds per 100 square feet of canopy or planting bed. August is a good time for a light application of fertilizer if you have been receiving rain regularly.