You know, I hate to sound ungrateful. We always need rain in New Mexico, if not to water all of the grass, trees and native plants, then to replace our valuable water tables. But in a climate of extremes, especially this summer, we’ve had several weeks of too much water and cool temperatures.
Typically, New Mexico and many Southwestern states receive monsoon rain in the summer, and it accounts for at least half of the rain we receive in New Mexico and Arizona. Monsoons can start around mid-June and end late in September. Ours typically begin around the 4th of July. Monsoons consist of short but strong bursts of rain, usually in the afternoon. They’re fueled by the sun’s warming of Southwest land and nearby oceans at different rates. Water evaporation creates humidity over land, forming the clouds that then depend on temperature, atmospheric pressure, winds and mountain slopes to turn into storms.
Typical is key here, however. This year, we had few to no monsoon storms. Instead, we had unseasonably hot and dry, followed by weeks of unseasonably cool and wet. The first rains did wonders at greening up our native grasses and plants. But then in August, the rain and clouds just kept coming. We just had a break, but now Hurricane Newton has struck Mexico and its remnant moisture is headed for southern Arizona and New Mexico.
If arid areas need rain, why is so much rain bad? Flash flooding is a big problem in desert and mountain areas. But how does heavy rain affect xeric lawns and gardens?
First, plant roots need more than water to survive and thrive; they also need air. When you place a new plant in the ground, for example, you should press the soil around it lightly and avoid compacting it to the point that air can’t reach the roots. When excessive rain falls, the water replaces air in spaces around soil particles. As the water drains through the soil, air can again enter the spaces. But if the water keeps flowing from the surface, or especially pools, the spaces fail to open. Eventually, roots can be damaged and fail to even take up the water that surrounds them.
The second danger of too much water is disease. Any fungal organisms in the soil can more easily attack wet plant roots and cause root rot. Xeric plants are not used to so much water on their leaves and roots. Even leaves are affected by too much water falling and sitting on them, especially without sun and heat to dry them again. Plants are more susceptible to leaf diseases such as leaf spot or blight and have less chlorophyll, which affects appearance and photosynthesis. Eventually, poor leaf health can lead to the breakdown of most of the processes that keep a plant healthy and send energy to fruit and flowers.
Many xeric plants also like sun and a little heat. Native plants have adapted to the Southwest monsoon patterns that usually rule their growing season: A gradual, sunny warm-up in the morning, followed by scattered building clouds. They get a nice drink in the heat of the afternoon, and then the sun comes back out and the air and ground warm up again. This pattern helps dry the plant and soil, and gives the plant plenty of heat and sun. Although nights can be cool in many areas of the high desert and intermountain regions, mornings warm up again after sunrise. Extended periods of cloudy, cool weather lead to too little sun for plants, along with too little heat than they need to thrive and flower.
Even edibles can have problems from too much water. They’re susceptible to root rot, depending on lots of other factors such as soil quality. Leafy vegetables and herbs flower early. Tomato fruit tastes better with moderate water. Too much water, especially inconsistent amounts, can cause fruit to crack.
Keeping Xeric Plants Alive During High Rain Periods
Make sure all plants, and especially those susceptible to root rot, are in soil that drains well. Raised beds, mounds or berms, and suitable containers can help drain soil around plants much better than compacted soil. If you’re not sure how well your soil drains, you can typically tell when it pools or soaks in hours after heavy rains. Or you can try the test in this handout from TreePeople that times water drainage.
Provide air circulation. We all have a tendency to place new plants and seedlings too close together. You might as well get as many cucumbers as possible in the limited space you have, right? But lack of air circulation in crowded plants hides bugs, causes the leaves to maintain moisture, and even can shade ground around roots. Wet conditions harbor new problems that native plants in particular can’t take.
Another problem with extended periods of rain is weed control. Although mostly native, the darn weeds seem to love excess moisture. And before you know it, they crowd and wrap around important garden plants or shading grasses. It’s hard to control them if the ground is too wet to mow or you can’t even get outside.
Build raised beds or transplant susceptible plants to higher ground. We’ve had some drainage problems near our patio and are working on a dry river bed to divert water away from the house foundation and down into a grassy area, where it can soak grass and eventually add to groundwater. One step we took was to divide a blue mist spirea (Caryopteris clandonensis) and move the portion near the patio onto a small burm. The xeric plant is so much happier now.
Whatever you do, don’t water! Turn off drip or sprinkler systems during and after periods of rain; it’s just the responsible thing to do. And don’t assume that yellowing leaves indicate the need to water. With too much water, the leaves look sort of floppy, but too little water usually causes dry, brittle foliage.
Finally, don’t stress. You can’t control weather, so simply keeping your plants as healthy as possible within time and weather constraints is all a gardener can do!