The key to gardening success is to install plants that are well-suited to the environment at the planting site. On the Big Island, elevation is a determining factor. Plants that thrive at 1,000 feet may not do well at lower elevations. If you are planting above 2,000 feet, you can often choose from plants that grow happily in temperate climates. Selecting plants that match your growing conditions usually means less stress for the plants and less work for you.
The key to gardening success is to install plants that are well-suited to the environment at the planting site. On the Big Island, elevation is a determining factor. Plants that thrive at 1,000 feet may not do well at lower elevations. If you are planting above 2,000 feet, you can often choose from plants that grow happily in temperate climates. Selecting plants that match your growing conditions usually means less stress for the plants and less work for you.
Your elevation can affect many growing conditions. Elevations below 500 feet in Kona usually have higher temperatures, limited rainfall, more alkaline soil, salty air and hours of hot sun. Mauka locations often have cooler days and colder winter nights. Sites over 1,000 feet get lots of summer rain, have more acid soil and an afternoon cloud cover almost daily.
Location as well as elevation can determine growing conditions. Many West Hawaii properties lack sufficient soil and are mostly rock. If the rock is not solid, new plants might be OK. Test drainage before planting by pouring a 5-gallon bucket of water into the planting hole. If it takes more than five minutes to drain, select another spot or plant a water-loving plant like a fern, ginger or heleconia. Most shrubs and trees will do better in soil that drains well.
Be sure that you consider the amount of sun versus shade in your planting site. A plant that requires full sun needs at least six hours a day of solar exposure. At upper elevations, it may need even more exposure to account for the afternoon cloud cover. Plumeria and bougainvillea prefer hot, dry spots and grow well at lower elevations. Anthuriums, however, need deep shade with plenty of water at lower elevations but can survive with only partial shade at elevations over 1,500 feet.
In the selection process, you might also want to consider disease resistant plants, especially in the case of trees that are vulnerable to anthracnose or the root rots that flourish in wet weather. Many varieties of fruits and vegetables have been cultivated to resist disease through natural breeding. You do not need to buy genetically modified plants to find disease resistance. In fact, many seed catalogs contain information on disease-resistant plants and most knowledgeable nursery folk will know the disease resistance of the plants they sell.
Many plants that you may have enjoyed in other climates may not be happy in the tropics. Plants that grow well in temperate zones often need a winter chill or even a freeze to go into dormancy and come out ready to flower and fruit. Before you purchase a new plant, research its preferences. Planting from seed gives you more varietal choices so you can best match your conditions to the plants’ preferences. Lettuce or herb seeds that are “slow to bolt” will stay in production despite the heat and not go to seed quickly. Knowing the plant’s native habitat can often help you understand its needs. Plants native to Hawaii or other tropical areas will likely do well here as long as you know their dryland versus wetland preferences.
Even though we have little seasonal variation, choosing the right time to plant can also affect your plants. Tomatoes and winter squashes (like kabocha) do best when planted toward the end of our rainy season when the weather is warm and the rain is frequent. When they begin to fruit, the cooler, dryer fall weather helps avoid rotting fruit and diseases that thrive in wet weather.
Be sure to consider the mature size of a plant in your site selection process. This will save you lots of pruning time, later. In coastal areas, below 500 feet elevation, installing drought-tolerant plants and an irrigation system will also help reduce your workload. Covering your soil with ground cover plants or mulch will keep the soil cooler and moister reducing water needs.
Healthy soil means healthy plants. If you suspect that your soil lacks sufficient nutrients, have your soil tested and apply the nutrients suggested in the report before planting. Adding compost in the planting hole and mulching around the root zone of the new plant can have a positive effect on its health.
Pest and disease worries will be greatly reduced if you have done good research. Maintaining your garden can be trouble-free if you’ve selected the right plants for the right place and have planted at a good time.
Tropical gardening helpline
Neil asks: We have a wooded area at the bottom of our property which is seriously infested with coqui frogs. In my hunting, I have noticed very few frogs on kukui, and none at all on silver oaks or Christmas berry. What sort of vegetation is most unfriendly to the frogs?
Answer: Sadly, coqui frogs continue to move into new areas in Kona during the rainy season. They love this wet weather. In drier months, they may retreat but they will return again when it rains. Knowing they like wet environments, it is probably best to simply avoid plants or environments that harbor moisture.
You can find some good advice at https://www.ctahr.hawaii.edu/coqui/eliminate.asp. It notes that frogs are attracted to plants that hold water in their leaf attachments. That would include most palms, ti plants, monstera, bananas, heleconias, all bromeliads and more. Leaf litter and mulch can also harbor frogs.
Kukui trees like a moist environment and thus may be found where frogs are. Kukui are not ideal for frog life unless the foliage is very thick with lots of places for them to hide. Christmas berry and silver oaks may have less frog hiding places, but they are both invasive weed plants. Choose trees or shrubs that have open canopies where frogs cannot hide at night when they are calling. Go to https://plantpono.org/non-invasive-plants.php for an extensive list of non-invasive plants.
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 local organic farmer, plant adviser and consultant.
Farmers markets
Wednesday: Hooulu Farmers Market, 9 a.m. to 2 p.m. at the Sheraton Kona Resort & 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
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 UH 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.