August 2010 Newsletter©

Watering Refresher

The experts say the first six months of this year have been the warmest on record.  Increased heat means increased water demand by your plants so I thought this month we’d do a little review on watering.

Plants move a great deal of water through their systems.   I’ve mentioned before that a mature oak can absorb as much as 400 gallons of water a day when the air temperature nears 100°.  Remember also that the root zone of that oak is approximately 2 ½ times the canopy width, so all your grass, shrubs, perennials and annuals nearby are competing for the same water.  The oak has nearly 625,000 miles of roots and feeder roots filling the soil around it, so is there any doubt about who wins the competition for water?

“How much do I water?”

We’d like to apply 1-2 inches of water per week to keep plants healthy.  Watering should be infrequent, but thorough.   Set up your sprinkler, place a couple of empty soup cans at different distances in the pattern, and let it run for an hour.  This will show you how much water is applied in an hour and if you are getting even coverage.  Try to apply between ½ and 1 inch of water each time. 

Some gardens will require more water because of the soil type.  Mine does.  I have a thin layer of soil on top of 8-12” of sand.  Three days after a 2” summer rain, I have to water.

“When is the best time to water?”

Watering in the day, before 4 PM, allows enough time for the foliage to dry.  That’s important in Memphis because we grow so many plants prone to leaf diseases.  However, if you are like me and work 10+ hours a day, six days (or more) a week,  evening is the only time I have to water.  Mother Nature waters 24/7, so if it needs water…water it, whenever you can!

“But if I water in the middle of the day, won’t the foliage burn?”

Absolutely…not!  No truth in that at all.

“But my Japanese maple has spots on the leaves where the sun burned it!”

The leaves are scorched, but not from water on the leaves.  Japanese maples like cooler soil temperatures than we have here.  When the soil temperature rises above 70°, the plant sort of “shuts down” to retain water.

Moisture is still being sucked from the foliage by sun and wind which causes brown spots and the edges to brown.  Lace leaf varieties are more prone to damage than others, but they all will “burn” to some extent.  It doesn’t hurt them and they will leaf out next year and look fabulous.

“How do you feel about irrigation systems?”

Irrigation systems are a testament to the fortitude of plants. Unless you change it, it puts out the same amount of water regardless of the temperature, whether it’s raining or not and it totally disregards the needs of different types of plants.  Plus, it does not compensate for new plantings.  As we said above, the average root zone on a plant is 2 ½ times the canopy.  If you have an established 3’ wide plant, the root zone is about 44 sq. ft.  If you plant a new 3’ plant from a 5 gallon container, its root zone is less than 1 sq. ft.  There aren’t any roots outside the rootball.  The established plant is receiving 44 times the water that the new plant is getting and they probably need the same amount.  Quite often we have customers that don’t understand why their new plant, under irrigation, dies.  “It’s getting watered!” yes, but not nearly enough!

That said, a properly designed irrigation system does an excellent job as long as it’s programmed to water deeply and the proper spray heads are used based on the needs of the plants.  Watering deeply is critical.  Frequent shallow watering requires more water because of evaporation and it causes roots to stay near the surface where it’s damp.  This makes them more prone to drought stress (which occurs year-round) and   winter-kill.

“So how can I tell if I need to water?”

Nothing beats the finger test.  Pull the mulch back and check the soil about knuckle deep.  If it feels moist, don’t water.  If it’s dry, water.  Pretty simple. 

Some plants will tell you by wilting, but that can be misleading.  Young hydrangeas will wilt in the sun even with moist soil.  They have lots of large leaves and the transpiration rate in hot, windy weather can exceed the absorption rate.  Once they are in the shade, they pump back up.  Once established (which can take several years), that should stop.

Some plants recover quickly from wilting but some do not, so you should avoid letting them wilt repeatedly.  Some don’t wilt, they just shed leaves.  Some drought stressed plants often shed the internal foliage.  This decreases the amount of water it loses. It is just the plant’s way of protecting itself… it doesn’t want to die.  And then some plants show no signs of drought stress until they turn brown.  So waiting for a plant to show stress is not always the best idea.

“Can I ‘over-water’ in this heat?”

Yes indeed you can.  Often we see plants stressed, or die, in the spring from excessive rain in the prior August and September.  In the spring, the air temperature rises quickly and plants flush with new growth.  But the soil temperature is cool and it’s usually wet, so there is minimal root development.  As the summer progresses, the top growth slows down and there is an explosion of root growth in the warm soil.

Many plants will not survive the warm soil being saturated in late summer, especially plants that aren’t native to our area and need better drainage that we typically have anyway…cherries, azaleas, boxwood, conifers, most perennials, etc.

Plants take in water through microscopic roots.  If these roots rot off, the plant can’t take in water and it dries up and dies in wet soil.  If these roots dry up from lack of water, the plant can’t take in water and it dries up and dies in dry soil.  The net result is the same… dead plant.  Dry plants need water to grow new roots.  Wet plants need air to grow new roots, but chances are good, whatever the reason, YOU WILL WATER A WILTED PLANT.   It may need air not water.  So a wilted plant needs water, but it may not need watering.  Is that clear as mud?

Your container plants are going to need more water and more fertilizer if you are relying on just a water soluble fertilizer.  The more you water, the more fertilizer runs out the drain hole.  You should be using a good timed released fertilizer in your containers, supplemented with bi-weekly applications of a water soluble fertilizer for flowering plants.   Foliage plants will not need the additional water soluble.

We have depleted our MSMA inventory. For crabgrass control in this heat, Image is the product to use.  It also helps control nutgrass and many tough broadleaf weeds like wild violets and Virginia buttonweed.  Once the daytime temps fall below 90°, we can use quinclorac/2,4-d/dicamba products to control both crabgrass and broadleaf weeds.

Sometime this month, apply Hi-Yield Weed and Grass Stopper with dimension for pre-emerge weed control in your lawn and flower beds.  Apply again in November to prevent annual bluegrass, chickweed and henbit in the spring.  Applications every 3 months will keep you virtually weed free.

This was last month’s contest.   This pretty little orange flowered plant is a dwarf pomegranate.

August contest:  What are these?

The contest ends on Aug 15^th.  Drop by either store to enter or you can email your entry to

questions@danwestonline.com. One winner, selected from all correct entries, will receive a

$25 Dan West Gift Certificate.

Thanks for shopping with us at Dan West.