Do All Your Plants Receive Sufficient Water When It Rains?

By Richard Flowers, ACCNP-Green Thumb Nursery-Ventura

With many areas getting unprecedented amounts of rain with flooding and mudslides, you need to stop and wonder do you all your plants in your landscape actually receive sufficient amount of water? Just because it may rain it doesn’t mean that all your plants will receive enough water. Thunderstorms can be very sporadic when they occur. Some areas receive an abundance of rain while other areas don’t receive any or very little rainfall. It is important to recognize that some plants in your landscape may actually need water even though it is or was raining. Just because the surrounding soil may appear to be moist doesn’t mean your plants are getting enough water.

Plants that are interplanted, massed or crowded with other plants, can block and deflect rainfall because their canopies can be so thick that water doesn’t actually hit the ground and deliver moisture to the roots. These are the plants you need to pay particular attention to because the plants may be actually on the dry side, even though it has been raining steadily.

Sometimes plants with large leaves might block the rain from getting into the soil. Because of this, the soil can still be dry, even after a period of heavy rain. Be sure to check those areas thoroughly be moving away the leaves and check the soil near the plant for adequate moisture. Just because the leaves are wet doesn’t mean the roots get water. Many areas in the landscape that are heavily mulched, and at such times rain that occurs may not be enough to penetrate the thick mulch layer. For that reason, it is wise to move the mulch away or dig through it and the soil checking both to see if it’s actually getting adequate amounts of moisture.

Moisture needs to be long enough to soak through the layers of mulch and reach the soil and plant roots. Think of mulch as a blanket, if you spill some water on the blanket and if the blanket is thick enough you remain dry. You need to apply more water so the liquid soaks through enough to wet your skin. This same concept can be applied to mulch. Another area of concern you may want to consider are plants that are under the canopy of trees or shrubs. Think of the trees as umbrellas, when you stand under the canopy of dense trees you remain more or less dry. With that being said, the soil underneath the said trees where the plants are remains dry, these areas should not be forgotten.

Certain areas of your landscape may have a rain shadow or microclimate due to the terrain, buildings, structures, shade cloth, canopy, or sheltered areas where these areas are direr or the water is reduced because they are deflected by the covering reducing the amount of water delivered to plants as compared to exposed areas. These drier areas should not be ignored. Potted plants underneath the eaves or overhangs do not get influence of rain water even though the surrounding areas are moist these protected areas need water.

The type of material a landscaping pot is made out of, for example, clay can be very porous and absorb moisture very quickly. These areas may need to be checked to see if it needs additional water during a rain storm. Plants in containers especially if they are crowded with lots of other plants, the leaves, and other plant material block the rain from reaching the soil. All of the leafy foliage covers the soil surface meaning that no rain really reaches the roots. And the bigger, more mature the plants, the more this will be the case. In this case it is wise to water by hand using a watering wand and target the water directly at the roots something the rain does not do efficiently. Most containerized soils need to be rehydrated after the initial watering so the entire soil from top to bottom needs to be uniformly moist.

Before and after watering, I like to do a finger test to check to see if the soil is actually wet. The top of the soil may appear to be moist but what is down below is what matters. So, don’t be fooled by rain! If you think it’s rained and you don’t need to water a container, you’re probably wrong. Remember you do not want sprinkle the leaves, instead you want to water at the root of the plant.

House plants and interior plants need water even when it’s raining. Also plants that are hanging because hanging plants usually dry out faster than other plants. Make sure to double check those individuals. Many times accompanied by a rain storm are strong winds that can dry out plants even during the rain. During this situation watering may need to be put in place. Likewise, when wind is accompanied by rain the rain can blow sideways missing the desired plants entirely. Then, again, you may have so much rain and runoff of the soil that occurs, resulting in plants actually not receive water at the root zone resulting in a dry plant.

After a prolonged period of very little or no rain clay soil can become rock hard and crack. When rain does occur, the water beads and flows off, not absorbing into the soil where the plant roots are. After when the rain subsides the soil is many times softer, you can reapply water, this water penetrates the soil easier. With that being said, it can sometimes be a good idea to  water your garden  after a period of rain. The ground will already be soft. This will allow the water to  penetrate deeper into the soil , so the plant’s roots will find it easier to take up.

Sometimes if a light rain occurs or a quick downpour happens, this type of rain may not provide enough water to soak or penetrate into the ground. You will need to check the moisture in the soil of the plant. If you are not sure, feel around the plant and dig down a few inches. If the soil looks and feels dry, your plants could use a good  watering.

Did you know that in most cases, a 1/4 inch of rain will be enough to avoid needing to water your garden for the day. If the rain is less than 1/4 inch, you might need to give it a little water. If it exceeds this amount, you don’t need to worry about adding more water. But remember to always check the soil beforehand. There are a couple of ways that you can determine the amount of water the rain delivers in the soil. One nifty way is to place equal size containers that hold water throughout your garden. After a rainy period, measure each of the containers. This will tell you how much water is collected in different areas throughout your yard and gives you an average. From there you can determine if the plants in that area actually need water or not. Another method which is more accurate is to use a bamboo stake or screw driver so you can tell how far the moisture penetrates the soil around your plant roots. The probe should penetrate the soil easily. If it doesn’t, the soil is too ry and will need water. When using such a probe it is best to insert the probe 1/2 way down the root ball and use the probe on all sides of the plant. You want uniform moisture on all sides of your plants. When you release the probe from the soil and see soil moisture on it, you are good with water at that time, if the opposite occurs, the plant is in need of water.

An inch of rainfall that infiltrates completely into soil will normally travel to a depth of a few or more inches for clay and clay-loam soils to several inches or even a foot or more in sandy and coarse, rocky soils. In compacted clay soils, 1/10 inch of rainfall may sit at the soil surface and partially evaporate when the sun comes out, or infiltrate to a mere fraction of an inch. Clay soils often absorb only a portion or a fraction of an inch of rainfall per hour, while sandy soils may absorb 2 inches or more per hour.

What does this mean for water availability to plants and plant benefit from rainstorms? Depending on many factors from soil type to runoff, it means that rainstorms providing about 1/10 to 1/2 an inch of water provide short-term water for lawns, small plants, and bedding plants, with some benefit to shrubs and trees but not sufficient water to meet needs for trees and larger plants, to refresh water reserves in soil, to flush salts from upper soil, or even to meet water needs for lawns and small plants for more than a few days to a week.

It is important to monitor the wetness of the soil and irrigate accordingly – it may have rained recently, but the soil may still be dry and in this case you should add additional water. Regularly check soil moisture to avoid under or  overwatering  – you cannot always assume that because it has rained,
your plants have enough water.

I encourage you to visit all areas of your own garden and become familiar and in tune with where the rain falls? , how much?, and whether or not all your plants are getting sufficient water?

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