Get It Growing News For 06/08/08
By Dan Gill
LSU AgCenter Horticulturist
Dry weather and high temperatures often make it necessary to water landscapes occasionally during the summer. Even established trees, shrubs, flowers vegetable gardens and lawns may need irrigation during especially long drought periods.
Still more critical is the need to regularly and properly water new plantings and plants growing in containers.
When it comes to recently planted lawns, ground covers, trees and shrubs, they will not make it through their first summer in the ground without supplemental irrigation. Their roots have not had time to grow out into the soil, and these plants do not yet have well-established root systems. With their root systems still limited to a relatively small area of soil, they are especially vulnerable to drought stress.
Trees
The first summer after planting is the most critical time for newly planted trees, and proper watering plays a major role in whether or not they survive. Here are two ways to properly provide water to newly planted trees during hot, dry weather.
For the first method, turn on a hose to a trickle, lay the end on top of the ground within 6 inches of the trunk, and let the water trickle for about 20 to 30 minutes.
The second method – the best I’ve found – is to use a heated metal skewer or ice pick to pierce 10 holes through the bottom of a plastic five-gallon paint bucket or similar container. Put all the holes on one side. Place the bucket next to the tree trunk with the hole side closest to the trunk. Fill the container with water, and the water will slowly seep through the holes to provide excellent irrigation.
Use either of these techniques during hot, dry weather whenever seven to 10 days pass without substantial rainfall. Then continue to water once or twice a week until you get a good rain of one-half inch or more. Drought-stressed trees may exhibit wilting, leaf drop, yellow or brown leaves, scorched leaf edges or even death.
Shrubs
Generally, newly planted beds of shrubs may be watered with soaker hoses or sprinklers, just as you would established shrubs. They will, however, need to be monitored more carefully and watered more frequently.
Situations can arise where newly planted shrubs are damaged or killed by drought stress despite your best efforts. Remember, all of a newly planted shrub’s roots are in a small area about the size of the pot the shrub was growing in before it was transplanted. This is especially true for shrubs planted after March because they have had little time to grow roots into the surrounding soil.
A shrub can use up all the water in its root ball and become drought stressed even though the soil in the bed outside of the root ball is moist. In this situation, it is best to water each shrub individually, as needed, with a hose trickling water as described for trees. (Leave the hose by each shrub for about 10 minutes.)
Watch new shrub plantings carefully for the same drought symptoms described for trees. Summer-flowering shrubs – such as hibiscus and crape myrtle – may abort and drop their flower buds if they’re drought-stressed.
Lawns
Summer is a great time to lay sod to install a new lawn or repair an established one. Just remember that newly laid sod needs special attention for watering.
Apply one-quarter to one-half inch of water every day for the first seven to 10 days after the sod is laid. Then apply one-half inch of water every other day for another seven to 10 days. Continue to irrigate the lawn with 1 inch of water once a week as needed to encourage the roots to grow deep into the soil. Do not water every day for more than 10 days, or you may encourage fungal diseases.
Containers
Watering plants in containers outdoors is a constant job during the summer. It is typical to water every day – even twice a day when weather is hot and dry.
How often you have to water is influenced by temperature, pot size, the type of potting soil, the drought tolerance of a plant, whether a plant is in sun or shade and how potbound a plant is. Plants need to be watered more frequently when weather is hot, the containers are small, a light soilless potting mix is used, plants are in a sunny location and plants are potbound. Clay pots tend to dry out faster than plastic or glazed ceramic pots.
To reduce how often you have to water outdoor container plants, you can use larger rather than smaller pots, choose a potting mix that retains more water, repot potbound plants into larger containers, use plastic or glazed ceramic pots and, if practical, move the plants into somewhat shadier locations.
Some gardeners have successfully rigged drip irrigation systems, available at nurseries and building supply stores, to water their container plant collections. Set the irrigation to come on with automatic timers, and these systems can greatly reduce the effort of keeping container plants watered. Self-watering pots that include a built in water reservoir also might work in some situations.
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Contact: Dan Gill at (225) 578-2222 or dgill@agcenter.lsu.edu
Editor: Rick Bogren at (225) 578-2263 or rbogren@agcenter.lsu.edu