Extension Report

County Extension Office

302A Byrne Street

Bay Minette, AL  36507

Telephone (251) 937-7176 or

928-0860/943-5061 ext. 2222

FAX (251) 937-7285

Beau Brodbeck

Regional Extension Agent

Forestry, Wildlife & Natural Resources

December 20, 2011

When Winter Is a Dry Time

We’ve finally started seeing some rain in central and coastal Alabama. We need it, but it hasn’t been enough. 2011 was a serious drought year for central and south Alabama and worse for Louisiana and Texas. At this time, the national forecast shows the same patterns of weather likely to return in 2012. This will add to the damage already done by the previous summer and winter drought of 2011. This leaves our trees, particularly our cityscape and small lawn trees, seriously dependent on our good will.

We’re mentioning this because we need you to do something important:  Water your trees this winter. Please.

You might think, “Wait, it just rained and its winter. Who ever heard of watering trees in winter?”

Drought doesn’t depend on heat to happen.  All it takes is a lack of rainfall over time. In Alabama, this is not usually a worry. The coastal regions typically get nearly as much rainfall as Seattle, Washington, and the interior a nearly continuous year-round supply of storms and showers.

Droughts, especially long term droughts, affect trees and other woody plants in serious ways. The effects are not usually immediate and one drought will affect the trees for years to come. Trees may not show the extent of these effects for 2 years or more.

Long term effects include:

• Dieback of branches
• Less foliage
• Increased susceptibility to pests
• Slowed growth
• Become unable to close wounds

Trees are very water dependent. They need a constantly replenished supply just to maintain themselves, even in winter. The trees here in central and coastal Alabama live in a much warmer climate than trees farther north.  The ground never freezes so their roots continue to grow. Many of our tree species retain at least some foliage all winter.  Those species that shed all their leaves still must maintain the tissues that will generate next year’s growth and keep all its water and sap carrying pathways completely filled. Water vapor escapes even thickly barked portions of the tree through special pores called lenticels.  So you see, all year long our trees require a steady supply of water.

Tree water requirements, particularly of large trees are substantial.  A full grown pecan tree can use nearly 200 gallons on a hot summer day, over the course of a year that same pecan tree will use between 3 and 6 thousand gallons. Thankfully, even a bad drought in the winter still means the trees aren’t using anywhere near this amount.  Wintertime water use of trees goes mostly to maintaining foliage for evergreens, keeping the spring growing points alive, and keeping the water carrying vessels of the tree filled and operating.

During a drought, the amount of water available in the soil declines to a point that the tree roots aren’t capable of absorbing it anymore. The soil ‘holds on’ to some moisture that only disappears when the drought becomes extreme. So you may think that the soil you are digging in shows some appearance of moisture, yet may not have any water in it that is available to trees or other plants. Just getting some rainfall doesn’t end a drought. Once the soil has dried, it actually takes repeated soakings for the water to finally percolate through and down, restoring the supply.  We often think of a storm or three as ‘breaking’ a drought, but really, the breaking only occurs after months of normal rainfall and the time it takes for the plant life to return to active, unhindered growth.

As the ground dries out, the root systems of trees begin to die back. Trees get nearly all their water through only the finest parts of their roots, the hair-like fuzz on the root tips.  Nearly all of the rest of the tree’s roots are armored in bark and don’t do much absorbing. The root hairs have to have a 100% humidity environment to live and do their important work of soaking up soil water and nutrients. Once the soil becomes too dry, these root hairs and even the fibrous roots die back to the structural root system. Once root loss has happened it will actually take days to weeks for the trees to re-grow the root hairs necessary to take advantage of rainfall.

So during the winter our best bet to help our trees is to maintain just enough soil moisture to keep our trees’ root systems lively so that they take advantage of any rainfall that comes along. Winter watering is much less intensive than summer. During dry times in winter (i.e. no rain in a week to two weeks), water trees in the morning or evening about twice a month.

Follow these tips for winter watering:

Water the entire growing area of your tree.  This is easy if you have a street side tree or tiny yard. If your tree grows in a large area, water an area roughly twice the size of its canopy. Any water is helpful, but tree roots extend out from the tree much farther than you might think. Covering more area is better.

Water newly planted trees, or trees that have been planted within the past 2 or 3 years more often. If we didn’t receive rain for a week; water them, paying particular attention to the root ball that was planted and the soil immediately around it.

Water deeply; a regular garden hose at municipal system water pressure should deliver

around 4 to 6 gallons per minute. If you aren’t using a sprinkler or a soaker hose, leaving the garden hose on at a trickle will work.  Check on it often. If water is standing on the soil surface, turn the irrigation off. The idea is to have water soak in deeply, maintaining the soil moisture.

Remember, the ideal plan is maintaining soil moisture, not trying to give enough water to sustain all of the tree’s needs. That would be a BIG water bill you don’t need. If you are using mulch around your trees, make sure you are watering enough that the soil beneath the mulch is being soaked. Mulches typically have to be wet all the way through before water can begin to reach the soil beneath them.

This article is co-authored by Jack Rowe, Regional Extension Agent in Forestry, Wildlife and Natural Resources at the Regional Research and Extension Center in Thomasville.

Email address: brodbam@auburn.edu

Phone: 937-7176 or 943-5061, ext. 2222

Baldwin County Extension Programs are supported by the Baldwin County Commission.

The Alabama Cooperative Extension System (Alabama A&M and Auburn Universities) in cooperation with the U.S. Department of Agriculture is an equal opportunity educator and employer.