Last year, folks were complaining about wet weather in West Hawaii and too little rain in East Hawaii. Now, West Hawaii is getting much more rain than usual. Even the haole koa and kiawe are lush green from makai Kona to Kohala.
Climate warming definitely seems to be affecting us locally, as temperatures have also hit record highs this year. 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.
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.
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.
Some plants are notably resistant to drought. 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 turning the leaf back or edge-on to the sun. Others root deeply to tap water in the ground and have it available for dry periods.
The garden environment is the other critical factor. Water use is a process controlled by energy. The source of that energy is the sun. The amount of energy available and the nature of the conducting medium that is the soil-plant-atmosphere complex determine how much water will be used in a given time.
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 can actually increase rainfall in places such as Hualalai, Kukio and Mauna Kea Beach when we change lava flows into “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.
Plants that are tolerant of salty beach conditions often use less water than many jungle plants because they are streamlined for water conservation. Beach naupaka is a great salt-resistant shrub that is also used in the landscape inland.
Plants such as the Bird of Paradise, Dracaena, Monstera and many Philodendrons give a luxuriant look and are still drought-resistant. Many palms also have this quality. Heritage plants such as noni, hala and kukui are very drought-tolerant but will also grow in our wet humid lowlands.
Relatively new plant introductions such as tropical Vireya rhododendrons have an amazing capacity for adjusting to environmental extremes. In wet areas they can grow as epiphytes. Under drier conditions they will grow as terrestrials.
Irrigate only when the soil water becomes low and plants begin to show evidence of wilt. Understand that we have to irrigate sooner following a previous irrigation than a general rainfall.
And provide soil with good physical and chemical properties for deep rooting of plants. 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 addition of this element is particularly important.
Using mulches will also help conserve soil moisture.
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!