Growing Roses in the Tropics

Roses indeed are associated with cool climates like San Francisco, Portland and even London. They will, however, flourish in a variety of climates in Hawaii. The early missionaries brought the older type of roses, not hybrids, to the Islands.  

In Hawaii, roses can flower throughout the year in the warmer, sea level climates. They can also be in continuous bloom in the cooler mauka (mountain) communities.

In order to reap the benefit of these beautiful flowers, some care must be taken when growing and maintaining the plants. Here are a few essential points to consider:
 

• Roses require at least six hours of sun each day,
•  a well-drained soil  and
• adequate protection from strong continuous winds                                             

Rose bushes grown with less sunlight than six hours will tend to be tall and leggy with fewer blossoms.

Roses will benefit from mulch 4-6 inches. This reduces the temperature of the root environment, helps to control weeds, supplies nutrients to the ground and improves the physical characteristics of the soil. 

A fertilization program should be guided by a soil analysis. For further information on nutrition, and other rose topics, including specific cultivar recommendations, the UH CTAHR (College of Tropical Ag & Human Resources) website has an old, but good publication entitled, Rose Growing in Hawaii.

Roses are seldom free of pest. This is especially true in the tropics. Chinese Rose beetles are frequent and serious pests which come out after sunset and chew on the leaves. Tiny spider mites, aphids, thrips and grasshoppers will also attack the plants. Diseases like powdery mildew, black spot and rust are common. The rust appears on the underside of the leave as powdery pustules of bright orange spores. Diseases are particularly difficult to control when rainfall is high.

Nematodes

 Nematodes are microscopic roundworms. There are both good and bad nematodes. Many nematodes live in our soils and are beneficial.  But there are a number of harmful species that attack plants. These nematodes insert their stylet mouth-part, much like a  hypodermic needle, into the  tissue and suck out the plant juices.  

Plants which are infested with nematodes may exhibit symptoms of stunting, yellowing and wilting. Further symptoms may be smaller and fewer leaves, and smaller fruit.  Also, due to this feeding, the root knot nematode, in particular, will cause the plant cells to rapidly enlarge, thus developing characteristic bumps or knots on the roots. 

What to do?  If root knot nematodes are in your garden, take it seriously. Eradicating the garden of nematode pests is highly unlikely, but they can be managed with good sanitary procedures. Here are some measures:

·      Apply organic matter (OM) to the soil.  OM will encourage the growth of beneficial organisms, fungi, bacteria and good nematodes. They, in turn, will ‘attack’ the plant parasitic nematodes and deplete their numbers. A note of interest, there is one species of fungus that forms loops with its fungal threads. Nematodes will become stuck in these loops, which will actually tighten, and eventually the nematode dies. 

·      Crop rotation  Do not replant the same crop or any susceptible crop into infested soil.  For instance, if you discover root knot nematodes on your cucumbers, plant a resistant crop, like garlic or corn, in place of the cucumbers. For best results, do not plant with a susceptible crop for 3 years.

·      Keep the soil fallow. A more drastic form of crop rotation is simply keeping the infested area fallow. This starves the nematodes. Do not allow any crop, even weeds to grow there. But do add organic matter. Again, 3 years is best.

·      Soil sterilization  This involves covering the infested area with a piece of clear plastic for at least one month and preferably two. This should be done during the hottest part of the year.  In hot climates with clear skies, enough heat can be produced underneath this tarp to kill most of the nematodes. 

·      Plan resistant varieties. The best control against nematodes is to use resistant varieties. You may notice on a tomato seed package the letters VFN.  This means that the variety is resistant to the fungus, Verticillium and Fusarium and to the root knot nematode.  Such varieties include Celebrity and Better Boy. Asparagus, corn, garlic, onion, strawberry, zinnia, salvia and marigolds are also resistant to root knot nematode.  

Most Important: DO NOT SPREAD CONTAMINATED SOIL

Perhaps the most important aspect of controlling nematodes is to stop them from spreading throughout the garden.  If your tomato patch is newly infested with nematodes, keep those nematodes there. Nematodes will slowly spread in the soil by themselves. Don’t help them by carrying soil from the infested area to other areas, or by carrying around contaminated dirt clinging to garden tools and shoes. Work in an infested area last. Always clean tools and shoes.  Be cautious when receiving potted plants from other gardens or even from a nursery that has non-sterilized soil.    

Marigolds have been reported for many years as a way of reducing the nemotode populations. The French marigolds are most effective; varieties include Nemagold, Petite Blanc, Queen Sophia, and Tangerine. Unfortunately, planting a few marigolds next to each susceptible plant will NOT eliminate the problem. To be effective, the entire infested area needs to be planted in marigolds, each plant about 7 inches apart. The flowers must be planted for a minimum of two months and then turned under. The area also needs to be kept free of weeds. Then, root knot sensitive plants can be planted back into that area the following planting season. Replanting marigolds every other year will almost certainly be necessary.   

Growing Corn in the Tropics

In Hawaii, as well as other tropical areas of the world, corn can be planted year round. This will give gardeners three and possibly four crops a year.  

A major complaint from backyard  growers, however, is that the individual ears of corn produce few kernels. Poor pollination is the most common cause. Since corn is wind pollinated, it needs to be densely planted in order to achieve good pollination. Planting a compact square or a dense circle will ensure better pollination than a few plants or long rows. The best recommendation is to plant a minimum of 4 rows about 8 feet long rather than 1 or 2 long rows.

Weather patterns can adversely affect the corn crop.  Too much wind or heavy rains during the pollination period, or very dry weather will impede pollination. In addition, from pollination to harvest, corn plants need adequate water to insure full kernel development.

Corn varieties are classified into two groups, tropical and temperate. The tropical supersweet corns are bred in Hawaii. Popular ones include Supersweet #9 and #10. If residing in the tropics, growers should be aware that many seed company catalogs list only the temperate hybrids: Bantam, Golden Cross and Jubilee. Some of these seed packets are also found in local stores. These temperate varieties have, in general, been very disappointing when grown in Hawaii and presumably in other tropical regions.