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Q. We've had some super hot and dry weather this summer. We get an occasional hit and miss shower, but some of my plants still look rough.  Will the plants in most landscapes survive the dry spells without supplemental watering?
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A. Yes, it has been a doozy this summer, so I am not surprised that your plants are showing symptoms.  Also, the problem has only been compounded by the fact that we had an unusually cool, wet spring before summer so the heat effect is exaggerated.  Plants became accustomed to just the right amount of rain, at just the right time.  With hot, dry weather, they have trouble acclimating themselves. Trees and shrubs that have been planted a year or less are the most vulnerable. However, plants that are well established and healthy can withstand much more drought stress. Of course there are exceptions to all generalities.

 

For instance, very well established Azaleas and Hydrangeas easily show drought symptoms. These plants have relatively shallow root systems adapted to semi-shady light conditions and moist (not wet) soil environments. Many times these plants are located in less than optimal landscape conditions and they suffer as a result from the heat of full sun. There are numerous other examples and plant needs must be looked on in a case by case basis. Therefore, it pays you to learn a little about specific plant needs prior to planting.

 

In the western part of the country many people have adopted a gardening practice called xeriscaping. I don’t really like the word for our region because it implies you must grow cactus or succulent plants only. Actually, the priciple is much more balanced and involves grouping plants by water needs and limiting heavy water use areas. It also involves implementing some very common sense water use practices. I have a few of these tips listed below and I encourage you to put them into practice.

 
  • Only water the plants – not the street or sidewalk. If you see water running down the street, your irrigation system needs to be adjusted. It could mean the water is being applied too rapidly for the soil to absorb or the sprinklers are not properly located and are simply aimed wrong.
  • Water plants according to their needs.  This means you need to know something about the specific plants in your landscape. Plants will be healthier and you'll have a lower water bill. Water no more than twice a week in any garden area, including established lawns, and only in the absence of rain. Set watering priorities - which plants will suffer first, and which are hardest to replace? Established herbaceous plants, like flowers, need water once per week, but established large trees can go much longer.
  • Warm season turf is tougher than you think.  Well established turf can be weaned off frequent irrigation by slightly raising the mowing height, reducing fertilization and reducing irrigation frequency while increasing irrigation depth. Zoysia and Bermuda grasses can be allowed to go dormant if you wean them off the heavy fertilization and irrigation regime that so many people have adopted. Centipede and St. Augustine are less drought tolerant and may need more irrigation to survive. Regardless of the type of grass you have, if we continue in a prolonged dry period, even dormant grass may need some supplemental water, but it does not need to stay green to survive.
  • Water during the coolest part of the day.  Water between 4 a.m. and 10 a.m. to decrease disease problems and water lost to evaporation. Some municipalities may regulate watering times. Set your timer to water during permissible time periods.
  • Use soaker hoses or trickle irrigation systems for vegetable garden plants. Drip irrigation and soakers put water where it is needed – the roots. Spray irrigation sprinklers lose lots of water output to evaporation and wind. Drip systems and soakers have the added benefit of applying the water slowly enough so that it all soaks in rather than running off the targeted area. This method is actually more efficient than hand watering.
  • Don't over water. However, make sure the water soaks into the top 8 to 12 inches of the soil, where most shrub and tree roots are concentrated. For turf, flowers, and other small plants, the water need only soak about 4 to 6 inches deep. Avoid frequent and brief, shallow watering which encourages shallow roots. This actually increases the chance of drought stress later should water become less available. 
  • Water based on the weather, not the clock. Use rain sensors to prevent your clock-based controller from watering during a rain. Check the soil periodically to determine moisture depth. Consider collecting rain water using rain barrels or a cistern.
  • Mulch!  A two to four inch mulch layer helps plants through weather extremes by moderating moisture loss and soil temperatures. Mulch as large an area as possible around trees and shrubs. Mulch is especially important to shallow rooted ornamentals like dogwoods and azaleas. But, don’t add too much.  Excessive mulch may have the reverse effect because the roots will grow up into thick mulch and die when it finally dries out during drought times.
  • Minimize gardening activities.  Avoid pruning (other than removing dead wood) and fertilizing in droughty weather. Pruning and fertilizing both stimulate growth, which can additionally stress plants. Also avoid planting and transplanting in dry weather. New plants thrive best with natural rainfall and mildconditions. Transplants require extra water for establishing newroots. Fall is still the best time to plant. Hold off until more suitable weather for any landscape improvements that involve setting out new plants.

All in all, this summer has actually been luxurious considering we had at least some rainfall in each month. In past summers, we've missed seeing rain for a month or longer. For more tips and information on drought tolerant plants visit the following link:
http://www.aces.edu/pubs/docs/A/ANR-1336/ANR-1336.pdf or call the Master Gardener Helpline toll free at 877-252-GROW.

Written by Bethany A. O’Rear of the Alabama Cooperative Extension System (ACES). She is housed at the C. Beaty Hanna Horticultural and Environmental Center, which is based at the Birmingham Botanical Gardens.


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