Monday, July 16, 2012

Water those ornamental trees...They are thirsty!

As a not so gentle reminder:  Water your trees and big shrubs, they are very thirsty.

Here in New England we are finally into the heat, and drought, that we typically get at some point during the summer.  Our last significant rainfall was June 26 when we received 1.40 inches of rain.  It was a heavy storm that brought rain quickly therefore not letting it soak in before running off into sewers.

The Blue Hill Observatory in Canton is one of the oldest weather recording stations in America and provides excellent weather statistics.  The graphs provided here are from Blue Hill.

In addition to the constant heat and humidity we have had in July, after an overcast June, we have been running above average temperatures and below average rainfall for the past seven months.  June was slightly above average rainfall, but more than half of that came in two quick storms.

Friends and Clients often say, "Doesn't my irrigation system provide enough water for my shrubs and trees."  The answer to this question is,  NO.

Irrigation systems, when properly utilized are mean't to keep your lawn happy and provide sufficient water for annuals, perennials and small shrubs.   The length and depth of watering are not sufficient for trees and shrubs whose roots extend much deeper than the 6-12" of a lawn.

In fact, it is dangerous to rely on irrigation system to water your trees and shrubs because the shallow watering brings the feeder roots up to find water in drought rather than keeping them deep and less susceptible to drought.

During this drought protect your investment in ornamental trees and your specimen shrubs with a deep watering.  For your Dogwoods, Japanese Maples, other special trees, specimen evergreens, and anything special in your yard, place a hose a foot or two from the base and turn the water on to a slow trickle (about a third of your average kitchen sink full pressure).  For your smaller trees and shrubs about an hour is fine, putting the hose to the other side after 30 minutes.  For your bigger trees, two to three hours is sufficient, also move the hose around the base and further out.

The purpose is to provide water deep in the root zone, several feet down, and out in the feeder root zone which can extend outside of the drip line (breadth of branches).  This area deep down usually will stay moist given normal rain and weather, but in extreme weather will dry out and cause damage to trees.  It cannot be re-hydrated with irrigation or light hand watering.  It takes a long time for water to get down two feet and to saturate the soil.

Stress and damage are not the only problems when trees dry out.  Healthy trees typically can deal with minor insect infestations, but when they are under stress, insects detect the changes and weakness and will attack them.  A good Arborist will allow insect populations to exist, rather than kill everything, but when trees are weak and stressed, the arborist needs to attack the insect populations because the trees cannot defend themselves.  The "apple a day keeps the doctor away" maxim, applies to plants as well.

Take a look around your property and look for the shrubs and trees that need this help and spend several evenings providing water directly to their roots.  Tie some string or colorful ribbon to the trees you want to water and remove when finished, so you won't skip plants because you forget which ones you watered over the days.  Don't rely on stress to determine which trees to water, because when stress appears often it is too late to save some branches.  This is especially important for evergreens that won't show stress or damage unless it is too late.

Big Rhododendrons, Azaleas, Mountain Laurel, Andromeda will also respond to heavy watering, but their roots are much more shallow, and therefore don't require as much deep water.

If we have an exceptionally dry summer , this might be required several times, but often one good deep watering is enough to keep everything happy.  Two years ago, we needed to water even our biggest shade trees and evergreens, but we would need a longer period of drought and heat for this to be necessary.

Spend this week and weekend taking care of your special plants, it is worth the price of having to replace just one special plant or losing the leader on a new growing tree.


  1. Have been checking in on your blog for ideas. Thanks for past postings and will be back. Here along the shores of Lake Michigan gardening is different from yours, but many of the same concerns. Jack

  2. I normally water only newer plants, but this year I am watering lke a lunatic. They had to scrape me off the ceiling after I got the last water bill. I'm especially solicitous of a new flowering dogwood I planted this spring. With this and other favorites, I like to take a soaker hose and make a circle about 12" away from the trunk. Good to know 30 minutes will do the job, I've been watering much longer.

  3. Great advice, but with my large property it is hard to do! I do water those thirsty plants like hydrangeas and also any newly planted specimens. I have found that native plants do better with taking the climate extremes. I dream of an irrigation system, which would certainly help.

    1. Until recently I managed a 33 acre estate in Brookline, a wealthy suburb of Boston, and when we saw drought developing we would triage those that were most susceptible and most valuable.

      Depending upon the size of your water supply, we could put out a dozen hoses trickling water during the day and cover lot of plants efficiently. At home your could get a 4-hose splitter for your spigot and run four hoses at once from each spigot. It becomes an all hands on deck drill, but the loss can be devastating if you don't help during a drought. The key is to get water to the right plants without wasting water.

      Regional native plants will do better in extremes, but it does not mean they are drought-resistant. They still need help in rain-deficient periods.

  4. Reed, Thanks for the advice and explanation. I watered all my flower beds this past week when I saw a number of new plants (like ferns and Actaea) with crispy leaf edges -- but that was a relatively shallow watering (90 minutes of drip from soaker hoses buried under the mulch). Since I live in the woods, I don't have any ornamental trees (kind of like carrying coals to Newcastle to plant trees here) and I think we've had a bit more rain than you've had down your way, but I'm going to give that big rhododendron that has never looked very happy a good long drink. -Jean