Too much rain stresses plants
RAIN, RAIN, go away – or at least don’t stick around the entire day. News flash: Be careful of what you wish for as it may come true.
It seems that, while rainfall generally has not lasted for a whole day on most recent occurrences, we have been receiving an overabundance of showers.
Yes, it has been a really wet spring but I figure I would rather have a spring that’s a bit overly wet than one that’s a bit overly dry. The memory of 2011, with its record-breaking 100-plus-degree temperatures and drought conditions is still too vivid for me to complain about.
I attended a cookout over the past weekend and I was asked by several folks if the overabundance of rain will harm plants in landscapes and gardens.
Heavy rains, particularly when they persist over an extended period, place stresses on plants in our landscapes. Plants native to drier climates are particularly vulnerable to this type of weather.
As plants need water, what’s the issue with too much rain?
Although soil may seem rather solid, there are lots of spaces between the particles. Depending on soil type – clay versus sandy – and organic matter level, the amount of open or air space in a soil will range from 25 to 50 per cent.
These spaces hold air and water and the roots of plants need both. Roots absorb oxygen from the air spaces in the soil.
When it rains or you water a plant growing in a container, the air spaces in the soil begin to fill with water and the air is displaced. Gravity pulls on the water and it moves downward. As it does, air moves back into the soil spaces.
If rain occurs frequently over an extended period, the air spaces in the soil are kept filled with water. This deprives the roots of the oxygen they need.
If these conditions continue long enough, the roots stop functioning properly and may even begin to die. Although the soil is filled with water, the roots will not absorb it. This can cause plants to wilt, even though the soil is wet.
At this point, the roots are also more vulnerable to attack by fungal organisms in the soil that cause root rot and other diseases. Rot infections are highly damaging to the roots and are often fatal.
Our major defense against this is to make sure our landscape plants are well drained. Whether we are planting shrubs, bedding plants, perennials, vegetables or ground covers, the beds we prepare for them should be six inches or more higher than the surrounding soil. Our primary tool to achieve this is planting in raised beds.
Raised beds drain faster and dry out more quickly than ground-level beds. I hear gardeners complain during dry periods that raised beds may need to be watered more often – and this is often true. Still, we can irrigate and make sure plants have adequate water.
Adding organic matter to clay soils on an annual basis will facilitate soil drainage in clay soils.
By the way, if you have an in-ground irrigation system, turn it off. Turn it on manually to water plants if necessary. This recommendation may sound too much like common sense but I have seen so many landscapes being irrigated while it was raining that I feel it necessary to point this out.
So, what have we learned? We must not forget to consider drainage when designing beds and choosing plants. Drainage issues are best addressed during the installation of the beds. There’s not much we can do to improve drainage once the planting is done.
Raised beds are the best way to ensure good drainage. If you have a low area that tends to stay wet and you don’t want to put in a raised bed, you can certainly landscape the area with plants that tolerate wet soils. It is often better to choose plants adapted to the drainage in an area rather than try to change it radically.
Sometimes you might need to install a drainage system. The best time to evaluate the movement of water from your property is during heavy rain after it has been raining for a while.
Put on your rubber boots and grab an umbrella and head outside. You will be able to clearly see how the water is flowing across your property, where it is exiting and what might be done to improve its movement away from the property.
Given the frequency of showers lately, you should be afforded an opportunity to inspect rainwater flow in the very near future.