We’ve had a lot of rain recently. Our orchards may be thriving but plants that prefer not to have constantly “wet feet” may be looking stressed. You can help your plants through rainy seasons by being sure your soil drains well. Add some cinder soil next time you plant and be sure to remove any soggy material that is in the root zone of your plants if it continues to rain.
Despite our fears about changing weather patterns related to what might be described as climate confusion, we will most likely get a few months of dry weather this winter. It seems that extremes might be the new normal. Lots of rain and flooding will likely be followed by periods of drought. What we do know, however, is that Kona is currently in a long period of declining moisture. Less rain overall and increasing temperatures do add up to a drier climate.
Dealing with excess rain and flooding today will probably not translate into a long-term issue for gardeners and farmers in West Hawaii. We are much more likely to experience hot, dry weather in the future. Add to the mix increasing development and a growing population and we may soon be experiencing water shortages.
More than half of the water used in Hawaii goes into our landscapes. This includes homes, parks, golf courses, school campuses, hotels and resorts. We could considerably reduce the amount of water we put into our landscapes with a few simple practices, as well as planting wisely. It may be time to consider changes in our gardens that reduce water use without altering the beauty of our landscapes as weather patterns change.
Xeriscape gardening is a way of describing practices that account for water shortages. The word xeriscape was coined by the water department in Denver in 1981 to describe gardening techniques designed to conserve water. Naturally, part of any xeriscape gardening practice includes installing drought tolerant plants. The Denver water department followed up by publishing the “Xeriscape Plant Guide,” which includes more than 100 plants that are colorful, beautiful and useful in the landscape. Most of these plants are not tropical, but many can be grown successfully here. Other books and website lists followed. Perhaps the best and most up- to-date resource is the new book “Plants for the Tropical Xeriscape” by Hawaii horticulturalists Fred Rauch and Paul Weissich. The book contains more than 1,300 photos as well as descriptions of plants that grow well here and require very little water.
In addition to choosing less thirsty plants, xeriscape gardening requires evaluating your current watering system and changing it to address the reduced water needs of drought-tolerant plants. Probably the most efficient way to water is to use drip irrigation. This means water is released directly into the root zone of your plants. Water is not wasted in spray evaporation or in sprinklers that hit hardscapes or otherwise miss their target. Once you have installed plants that require less water, changing to water-saving irrigation methods to reach them should be easily accomplished, especially with the help of a qualified irrigation specialist.
You may also find that a lot of your existing plants can survive and do well with less water. Changing to drip irrigation on individual plants can wean them from the overwatering that is standard practice among gardeners in Kona. Consider replacing some or all of your thirsty lawns with drought-tolerant ground covers or beds of attractive succulents or cacti.
Conserving the water you apply to your plants is another way of saving this valuable resource. Mulching is an excellent water conservation practice. Applying a minimum of three inches of organic material in the root zone of your vegetable garden, shrubs and trees offers many benefits in addition to water conservation. The mulch will keep the roots cooler while maintaining moisture and encouraging microbial activity. All this will result in healthier soil and healthier plants, able to deal with the changes in climate we might experience.
tropical gardening helpline
Doug asks: Many of the greens growing in my garden have white spots on them. I have never seen this before. I think it might be white rust brought on by our very rainy summer. What can I do about it?
Answer: White rust, Albugo candida, is a water mold or oomycete that causes chalky white spore masses that first appear on the underside of leaves. These blister-like masses are under the epidermis of the leaf and can’t be scraped off without damaging the leaf. The spores of the pathogen are released when the blister ruptures and they are then carried throughout the garden by wind or splashing water.
Plants susceptible to white rust include members of the Brassica, or mustard, family including cole crops and cruciferous vegetables. The stems, flowers and seeds of host plants can also be affected. White rust disease can cause vegetables like broccoli and cauliflower to produce deformed heads and sterile seeds. Cool and damp nights and warm days are idea conditions for white rust. These are also ideal growing conditions for the greens and vegetables that host this disease.
If you have white rust disease in your garden, you should remove all infected plants and try to find resistant species for future plantings. Plowing or disking diseased plants and plant parts into the soil causes rapid decomposition of infected tissues and can help reduce future white rust infection. Removing garden debris and weedy areas that may harbor spores can also lower spore counts. Solarizing the soil between plantings is one way to kill most of the white rust spores in the soil. Remaining spores can lie dormant in the soil for years, however, and “bloom” again when ideal conditions occur. Crop rotation can also be helpful at controlling white rust. Infected beds should not be replanted with cruciferous vegetables for at least three years. Starve the disease by planting crops that are not susceptible to it.
Fungicides used to treat downy mildew are sometimes effective against white rust, particularly on leafy crops. Copper is an effective organic treatment as is a product containing Bacillus subtilis called Serenade. Applications of oils, like neem, can also help. Begin treatment at the first signs of infection.
Email plant questions to konamg@ctahr.hawaii.edu for answers by certified master gardeners. Some questions will be chosen for inclusion in this column.
Diana Duff is a plant adviser, educator and consultant living on an organic farm in Captain Cook.
Farmers markets
Wednesday: Hooulu Farmers Market, 9 a.m. to 2 p.m. at the Sheraton Kona Resort and Spa at Keauhou Bay
Wednesday: Sunset Farmers Market, 2 p.m. to sunset at the north makai corner of the Kmart parking lot
Saturday: Keauhou Farmers Market, 8 a.m. to noon at Keauhou Shopping Center
Saturday: Kamuela Farmers Market, from 7 a.m. to noon at Pukalani Stables in Waimea
Sunday: South Kona Green Market, 9 a.m. to 2 p.m. at Amy B. H. Greenwell Ethnobotanical Garden in Captain Cook
Monday to Saturday: U-Pick greens and produce, 10 a.m. to 4 p.m. Tropical Edibles Nursery in Captain Cook
Plant advice lines
Anytime: konamg@ctahr.hawaii.edu
Thursday: 9 a.m. to noon at the University of Hawaii Cooperative Extension Service in Kainaliu, 322-4892.
Monday, Tuesday and Friday: 9 a.m. to noon at UH CES at Komohana in Hilo, 981-5199 or himga@hawaii.edu.
