Don Gabel is NYBG’s Director of Plant Health. He monitors, diagnoses, and prescribes treatments for all the plants growing on the grounds, as well as in NYBG’s beautiful gardens and glass houses. Don educates and provides horticultural advice to the staff as well as teaching the public about different aspects of horticulture. He lives in Rockland county New York.
The other day, a friend asked me how much he should water his plants. And oh boy was that a loaded question. “Sit down,” I said. “This may take a minute.”
Most plant enthusiasts would agree that this is not always such a cut and dry subject. What comes to mind is the litany of questions I would want to ask before coming to any sort of conclusion.
- • Are we watering to establish the plant, or is it already established?
- • Is the plant container-grown?
- • Is it a tree/shrub or greenhouse potted plant?
- • If it is a potted plant, is it root bound? Or over potted?
- • Is it field-grown?
- • What does the ball soil texture look like?
- • What is the native soil structure like?
- • What is the sun exposure?
- • Is the ground sloped or raised?
Some general rules will help sort this wet and wild subject.
Pay attention to the weather, humidity, and sun exposure (length of time and position). These are critical factors in figuring out how much and how often to water your plant. Too much water excludes oxygen from the soil and promotes disease; too little and the plant is limited in function. Different soils become wet and hold water at different rates. When watering in-ground, remember that water will move laterally in similar soils before it moves downward into a different soil type. As a consequence, short periods of light watering in a landscape setting may not allow the water to move downward in the soil. Factors such as slopes and raised beds will cause the soil to dry more quickly.
When watering to establish a plant in the landscape, you should water the existing root system as well as the surrounding soils to attract roots to grow into the new soil. Allowing the root ball to go a little drier than the surrounding soil will help stimulate the roots to search out water.
Established landscape plants should only need extra water in drier periods of the year. Often that means July and August, but drought could occur at any time. Remember to water deep and over a wide area of the root zone and surrounding soils.
Container grown plants are grown in a “soil-less mix.” These mediums are designed to quickly drain away excess water and retain enough water for the plant to use for a period of time. For the most part, plants in containers come with all their roots. Factors such as soil mix, pot size, root condition, plant size, and sun exposure will all affect the watering needs. Darker colored pots will also heat up tremendously and may fry the roots at the edge of the container.
Plants that are dug out of the ground (balled and burlapped, or “BB”) have a majority of their roots cut, specifically the smaller water/nutrient-absorbing roots. New roots will appear at the cut and you should make sure that this area is irrigated. When planting out containers or BB plants, remember that the soil is most likely to be quite different from your native soil. As a result, they will wet and retain water differently in your planting. Remember to water well enough to wet all soil types, and if surrounding soil is dry, wet a broader area.
At this point, my friend—visibly overwhelmed—said rather unconvincingly, “Okay, I think I got it.”
Another “simple” gardening question with a not-so-simple answer.
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