There are many things in the garden that you can control, but the weather is not one of them. Even one excessively rainy day can affect plant health. University of Hawaii master gardeners in your area can answer questions relating to stressed plants due to the weather. Here are some issues that may arise in heavy rain.
Oxygen plays a vital role in plant health. Excessive rain can deplete oxygen in soil. When oxygen is depleted, root systems that take up water and nutrients to sustain plant life suffocate. Plant roots thrive in loose soil, rich in organic matter and alive with microorganisms. In healthy soil, organic matter decays and breaks down, a process in which oxygen is a key player. It is also needed for a thriving microorganism population. Without oxygen, plants become stressed and may die.
In flooding rain, plant leaves and stems can be submerged, and the vital process of photosynthesis, which requires light and oxygen, is impeded and causes additional stress to the plant. Plants that suffer from excessive water stress are also more susceptible to fungal and bacterial infection. Root rot and crown rot are common in wet soil. Even after the rain has stopped and water has receded, it can take weeks for the soil to dry out. Stress from excessive moisture can cause a plant to die, but it may take weeks or months to see the first signs of decline.
Soil and rocks can be shifted onto plants, thereby damaging them. Runoff can cause the roots to be exposed to the air. Preventative measures include mulching established landscape beds and rerouting water to drain off the property, or better yet, to a rain garden.
Some plants are more tolerant of flooding during winter months, when trees and shrubs aren’t growing as actively as in peak flowering or fruiting stages in Hawaii.
Starting a garden log or diary of weather events and plant health is essential to understanding your garden. Some elements of a garden log might be time of planting, soil amendments, insect identification and a regular monitoring schedule, notes on signs of disease or decline and any weather events.
Regular garden notes will very clearly lead the gardener to the cause of the decline, and then steps can be taken to avoid a future problem or repeat a success. UH master gardeners are trained to ask investigative questions to help gardeners find the cause of plant decline. A garden log ensures that you have the answer to their questions.
Mulch has the capability to balance soil moisture — it can both wick excess moisture from the soil and ensure adequate levels of moisture remain within the soil.
Keep track if your plants are declining in one area, especially a low-lying area where water collects after rainfall.
Time and Hawaiian sunshine may be your best solution.
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Jayme Grzebik is an Urban Horticulturist with the UH CTAHR Cooperative Extension Service and Statewide Coordinator for the UH Master Gardener Program. She can be reached by emailing grzebik@hawaii.edu
