Easter and spring remind us that our gardens burst with new life even in the tropics. It brings out the best in our nature. However, it is important to know how to keep our landscapes happy.
Last year, parts of the island were suffering from too little rain. Now West Hawaii is getting greener. Even the Koa Haole and Kiawe are lush green from makai Kona to Kohala. East Hawaii was having a dry spell but this spring it received almost too much. Climate warming definitely seems to be affecting us locally as temperatures have also hit record highs in the last few years. How does this affect our gardening practices and our state of mind?
We should remember that a healthy green landscape helps minimize the extremes of hot and cold. Vegetation helps reduce noise and pollution, and produces oxygen that makes us feel better. Also the color green is a very restful color.
The urbanization of Oahu is impacting the climate as more concrete and asphalt create desert-like conditions. On Hawaii Island we have vast areas that are covered with lava as well as pasture lands that were once forest. Reforestation can help increase precipitation as several studies show.
With water rates on the increase, some folks might consider concrete lawns! But don’t be hasty. You can have a beautiful garden even if you live in a drier area. It’s just a matter of planning and proper planting.
A garden planted with no thought given to dry spells will do well in rainy periods but deteriorates without irrigation in dry periods. Even in East Hawaii, we need to use plants that will tolerate extremes of wet to dry conditions. Fortunately, many garden plants in Hawaii are fairly hardy when it comes to short water supply, so we have a long list from which to draw. It’s important to vegetate these areas so that our islands don’t look like Arizona in years to come. A good reference to help you select the right plants is “Sunset’s National Garden Book”
There are two factors that make plants able to survive moisture stress.
First, some plants are notably resistant to drought. This quality is centered largely in the cellular structure and has a bearing on the economy with which the plant functions. Some plants have the ability to carry through extended dry periods because of a happy faculty of closing the pores of the leaf against transpiration, or they can turn their leaves back or edge-on to the sun. Others root deeply into subsoil to tap accumulated moisture and make use of it during the day.
The garden environment is the other critical factor. Water use is a process controlled by energy. The source of that energy is the sun. To move water out of the soil directly or through the plant and away into the atmosphere requires energy. The amount of energy available and the nature of the conducting medium that is the soil, plant and atmosphere complex, determine how much water will be used in a given time.
This is why the more shade and wind protection from trees we have in our gardens, the less water is required to keep moisture levels up. And conversely, the more asphalt and concrete to heat up, the more rapidly our planted area dries up, even in normally high rainfall areas like Hilo. Our lava lands are unusually prone to moisture loss, so when we develop these areas and plant trees, shrubs and grass, we actually create a cooler more comfortable environment. We may increase the rainfall in places like Hualalai, Kukio, and Mauna Kea Beach when we change lava flows to develop urban forests, parks and gardens.
Besides the moisture of the soil, the nature of the plant itself has considerable effect on the amount of water lost into the air. The height of the plant and the roughness of the surface have an effect on the wind movement and mixing of air across the surface of the vegetation. A rough surface will cause more water loss than a smooth surface.
What can we do in managing the soil to take advantage of our knowledge of the factors affecting water use rates? First of all, we can irrigate only when the soil moisture becomes low and plants begin to show evidence of wilt during the hottest part of the day. This forces deep rooting. Daily watering tends to promote shallow roots.
Proper fertilization will help accomplish this. Also, poor soils should be improved with the necessary amendments to help the plants develop good root systems. Addition of well-rotted organic matter or compost often helps increase moisture and nutrient holding capacity. In many Hawaiian soils, available phosphorus is lacking. This is essential to root growth, so the addition of this element is particularly important. The use if mulches will also help conserve soil moisture.
Proper planning and maintenance of your garden will help in the short run, but we must do something about the overall future of the islands as well.
For our mental and physical health, we need to focus on our own gardens and at the same time, work with our local politicians and planners to keep Hawaii the green paradise it is meant to be!
