Growing tomatoes in isles requires a bit of legwork

Fresh, ripe-on-the-vine, plump and nutritious tomatoes are tempting to anyone planning a vegetable garden. As many a frustrated gardener has discovered, however, there are numerous challenges to successfully growing tomatoes in the islands.

Choosing a site with good drainage and at least six hours of sunlight is an essential starting point. So is soil fertility. Tomatoes grow best in acidic soil with a pH of 6.0 to 6.8. If you don’t know the pH of your soil, you can have it analyzed through your local extension office or a commercial laboratory. Learning the levels of your soil’s vital nutrients — phosphorus, potassium, calcium and magnesium — also will be most helpful as you provide the best environment for your tomatoes to thrive.

Before planting, amending the soil with good compost and chicken manure will increase yields and provide a healthful environment for the tomato roots.

Selecting tomato varieties that have been specially developed by the University of Hawaii for local growing conditions increases your chance of success. Several hybrids, as well as the varieties Anahu, Healani and Kewalo, are resistant to root-knot nematode and other tomato diseases common in Hawaii.

UH Master Gardeners, trained in integrated pest management, typically suggest nonchemical, environmentally friendly strategies along with organic, soft chemicals as a first line of defense to prevent and combat plant pests and disorders.

Here are some tomato-growing questions fielded by Master Gardeners in West Hawaii:

Question: We first noticed some small white spots on the leaves a while ago that spread to the entire leaf, which withered and died. What can be done?

Answer: From your description and photos it appears to be powdery mildew, which commonly affects tomato plants. The symptoms are whitish powdery growth, distortion and leaf drop. Remove any diseased leaves from the plant and ground, place them in a plastic bag and dispose of them in the rubbish to prevent the spread of fungal spores.

For control, mix one tablespoon baking soda with 2 1/2 tablespoons of vegetable oil in a gallon of water. Spray the plants thoroughly, especially the underside of leaves, in the early morning or late afternoon every seven days for three weeks. If you are using clippers, use a mild bleach solution to sterilize them after each use.

Q: Spider mites have overrun my tomatoes. I tried a neem-concentrate mixture to get rid of them, but it isn’t working. What do you recommend?

A: Try using wettable sulphur, a safe and naturally occurring element, on them. Be sure to read the label and follow the instructions.

Q: I have been trying, without success, to grow tomatoes in our garden and also planted them in containers. The plants grow, and then all of a sudden they just wilt and die. I have been told we have nematodes. What can we do?

A: Given your description and without seeing your plants, here is some general information that may be of help:

» Bring an entire plant that is not completely dead to your nearest UH Cooperative Extension Service Office. Be sure to include the roots so we can check for nematodes.

» If you are going to use containers and suspect nematodes in your garden soil, start with clean containers and use sterile potting soil sold in bags.

» Problems can be minimized by using varieties resistant to or tolerant of diseases, such as cherry tomatoes and those developed by UH.

» If possible, irrigate only the soil and avoid wetting the leaves. Incorporating manure or compost into the soil will increase the microbial activity to suppress nematodes and improve root health.

Find more information about insects and diseases affecting tomatoes on the UH website: www.extento.hawaii.edu/kbase/crop/crops/tomato.htm. To find a Master Gardener Helpline near you, go to www.ctahr.hawaii.edu/uhmg/index.asp.

Celeste Makrevis is a West Hawaii Master Gardener. Ty McDonald is a University of Hawaii extension agent and Master Gardener coordinator at the Kona Extension Office.