As the new year dawns, think of the trees in our gardens and on our lanais that provide important shade, shelter and other benefits. Studies have described the financial benefits of trees, due to their abilities to capture pollutants, provide cooling shade, sequester carbon and for their aesthetic beauty. Honolulu’s Mayor Caldwell has announced a commitment to plant 100,000 trees by 2025 and increase tree canopy cover from 25 to 35 percent by 2035.
The first Saturday in November is Arbor Day in Hawaii. At last year’s events throughout the state, many people took home a free tree or shrub to plant. The selections included fruit trees, ornamentals such as tiare gardenia, and native Hawaiian plants such as kou.
Like all living beings, trees will thrive with proper care. Whether planting a new tree in your garden or maintaining an old family heirloom, follow some basic guidelines to care for trees.
IT STARTS WITH THE ROOTS
Trees kept in their containers for too long can become “pot-bound.” When roots circle inside the pot and grow excessively thick, they can lead to poor root systems when the tree grows larger. When you buy plants, don’t buy trees or shrubs that look too large for their containers or like they have been sitting in their pots for too long. If you want to keep the tree in a pot for a while, make sure to transplant the tree into a larger pot as it grows bigger. You may need to inspect the roots and prune or disentangle them when transplanting the tree. If you prune roots, prune back the branches by roughly the same percentage to balance out the demand for water and nutrients.
PLANTING PROPERLY
Give your tree space from the house, walls, pavement, pipes, electric lines, pathways with heavy traffic and other infrastructure. Trees come in all shapes and sizes. Do some research to find the right tree for your space. Trees will always benefit from greater access to uncompacted, healthy soil — try to avoid the typical city street tree practice of planting in a tiny tree-well or narrow strip between pavement. Tree roots do not look like a mirror image of the branches. They tend to grow opportunistically wherever nutrients, water, and air can be found, whether within the tree’s “dripline” (edge of canopy) or much farther away. More tree roots will grow outward in the top several inches of soil, rather than down deep.
Some old tree-planting advice was to dig a deep hole and mix in lots of compost and fertilizer. This can actually cause problems as the compost will decompose over time, possibly leading to subsidence. During heavy rains, the soft, rich soil can also fill up with water before draining into the native soil, drowning the tree. Instead, dig a wide, shallow hole, exactly as deep as the root ball (the soil and roots inside the pot). After placing the tree in the hole, fill it in with the original soil, gently packing the soil in to minimize any large air pockets. Apply about a 3-inch layer of organic mulch such as chipped and shredded green waste. Never pile mulch against the stem or trunk of the tree, as that may lead to disease. HECO has an excellent brochure called “Planting the Right Tree in the Right Place,” which can be found online. Please read this for detailed instructions on tree planting and other considerations.
PROPER PRUNING
Train them from a young age for optimal results. While every tree is different, many fruit trees have some basic guidelines. Typically, pruning is best done after the harvest is over. Cut out dead wood, branches that are crossing and getting tangled inside the canopy, and water sprouts or suckers, which are the fast-growing, green shoots growing straight up from main branches or the trunk.
Pruning takes some knowledge and experience. Learn some of the basics by reading CTAHR’s publication, “Pruning Trees and Shrubs,” available online. If you need help or need to prune large or valuable trees, hire a certified arborist to do the job properly. The Aloha Arborist Association maintains a list of its members who are certified. Online reviews can be found on websites such as Yelp by searching for “tree care” or “tree services.” While these services can be expensive, it’s worth it when you consider the benefits your trees provide.
COMMON MISTAKES
One of the most common errors is injuring the bark with a string trimmer or mower. Avoid driving and excessive foot traffic over the roots, especially close to the trunk. Consider whether the tree has adequate space, light, water and nutrients. Remember that urban trees are often subjected to harsh conditions such as compacted soil, flooding or intense heat from buildings and pavement.
With these considerations, we can take better care of our trees and enjoy their rewards. To learn more about trees contact the University of Hawaii master gardeners on your island by checking our website: ctahr.hawaii.edu/UHMG.
Kalani Matsumura is a junior extension agent with the University of Hawaii’s College of Tropical Agriculture and Human Resources and coordinates the UH Master Gardener Program on Oahu.
