Monday, August 12, 2013


Gladiolus is relatively easy to grow.  They, gladioli, require well-drained soils in a sunny location. While often classified as bulbs, gladiolus are actually corms, enlarged stems. Corms which have a plump shape with high centers are better than large, flat ones; the thicker the corm is, the higher the quality of bloom will be.  It is best to select corms 1 1/2 to 2 inches in diameter. They will produce full, attractive flower spikes. Small corms produce foliage but may not bloom.

Planting depth varies with the size of the corms. Large corms should be planted 4 to 6 inches deep and 6 inches apart. Small corms should be planted at a depth of 3 inches and about 2 inches apart.   A general rule of thumb is plant deeper in sandy soils and shallower in heavy soils.

Gladiolus may fall over because of the weight of the blossoms if the corm is not planted deep enough. The remedy, of course, is to plant deeper for better support.  If the soil is rocky, and it is difficult to dig a deep enough hole, the plants will require staking. 

The pest that primarily attacks gladioli are called thrips. They are tiny, slender black insects, about 1/25 of an inch long, obviously, difficult to see with the naked eye.  Thrips cause white specks or streaking on the leaves and blooms. Flowers can also be misshapen, discolored and occasionally will fail to open. 

Thrips feed by puncturing the plant tissue and sucking out the cell contents.  Preferring to feed on rapidly growing tissue, thrips often cause stunting.  These insects are the culprits which also cause silvery to brownish scarring on avocado and citrus fruit surface, but this cosmetic damage does not harm the internal fruit quality.

Horticultural oils, azadirachtin (Safer BioNeem), neem oil and insecticidal soaps can be somewhat effective for the temporary reduction of the number of thrips if applied when damage first appears. Sprays must be applied to thoroughly cover susceptible areas of the plant including new leaf growth and buds.  Note: these insecticides only kill newly hatched thrips and recently emerged adults, thus repeat applications are required, usually 5 to 10 days apart depending on the temperature. Moving the location of the gladiolus bed each year will discourage the spread of thrips.

Avoid the use of insecticides such as malathion and carbaryl: 1) they are highly toxic to natural enemies, 2) can cause dramatic increases in spider mite populations, and 3) are generally not effective against most thrips.