In the cultivation of plants and trees, the provision of adequate water and in some cases supplemental drainage is of utmost importance. While most people associate irrigation and drainage issues with the cultivation of lush green turf lawns, trees are no less dependent upon these two critical factors for proper growth and development.
Too little water and a drought condition ensues too much as under flooded conditions, and oxygen levels within the soil become deficient, thereby suffocating roots and increasing the rate of respiration (process by which trees convert sugars and carbohydrates into energy for life functions).
After just a few hours under flooded conditions photosynthesis stops (process by which trees use sunlight, carbon dioxide and water to manufacture sugars and carbohydrates), transpiration slows (water vapor loss through leaf stomata ). Also some micro-organisms are inevitably lost. After several days most species will sustain some root loss.
Flooding is not the only cause of overly saturated conditions. These can also be attributed to applying too much water at too frequent intervals, the overall grade of the land (trees growing in low lying areas ), grade changes due to construction and poor soil quality (heavy clay based soils). Soil compaction can be a factor as well. Trees that have endured flooded conditions are prone to toppling due to root loss and overly wet soils. They also suffer a higher incidence of root rot as a result of reduced oxygen availability
Water requirements of trees vary by species and age, as well as by numerous environmental factors ( temperature, relative humidity, light and wind). Newly planted or transplanted trees (of any species) require frequent watering, especially within the rootball. Watering mature trees with the same frequency however can lead to problems. It is important to remember that frequent shallow waterings encourage surface rooting (those pesky roots you keep tripping over). This also makes the tree more suceptible to desiccation (drying out) during extended periods of drought. It is a much better idea to provide infrequent deep soakings to encourage the development of a deeper, more productive root system (more drought tolerant trees). If soil is allowed to dry between waterings, the natural swelling and shrinking of roots serves to improve soil structure. On the other hand, frequent shallow watering tend to compact soil surfaces thereby reducing the rate of water infiltration.
The best time to irrigate is usually in the early morning, or late at night, but morning is best, as night time watering can sometimes create conditions favorable for fungal infections. There are many forms of irrigation, sprinkler irrigation being the most common. One disadvantage of this type of irrigation however is soil surface compaction, which is created by water hitting the soil surface and dispersing soil aggregates, which can lead to problems.The use of mulch can minimize erosion and soil crusting from this type of irrigation. Also, less frequent waterings of longer intervals will lessen the chance of salt build up.
High pressure water injection is another method, and as mentioned in our section on fertilization can be used in conjunction with liquid or granular fertilizers to provide a long interval feeding to tree roots.
Drip irrigation is another fine method which reduces water consumption and allows more water to be absorbed by roots with less water loss through evaporation or run off. Any drip emitters should be spread evenly over the entire root zone, and in no wise be placed near the tree trunk. These should ideally be moved outward each sucsessive growing season as tree roots expand and grow.
Interestingly enough the symptoms of drought closely mimic the effects of flooding or over saturation. These can be wilting, reduced growth, and twig and stem die-back among others.
( Charts displaying photosynthesis and water loss through transpiration )
In this condition the tree uses energy faster, and is inevitably weakened. If conditions persist the tree will begin to decline and eventually die.
(The growth rate of these trees has been reduced as a result of prolonged water depravation typical of many trees in and around parking lots and other developed areas. In these areas the heat island effect created when heat that has been absorbed from sunlight is radiated back to space from black top and other hardscape surfaces. This condition will only serve to increase the trees water demands.
( Willting leaves are a sure indication of water stress )
( Branch dieback can also be a symptom of chronic water stress )
(This tree is in a severe water defecit if remediation is not made soon this tree will not survive.)
Soaker hoses are another good method but if these are used water should be applied at a slow trickle. Basin irrigation and temporary portable drip systems used for the establishment of young trees are other good methods but these are usually used for single trees or in small landscape areas.
Most irrigation systems are installed as you might have expected, primarily in turf areas. Too often the irrigation needs of trees are not given proper consideration and as such, these systems are often insufficient, regarding application techniques and rates.
In our resource conscious world, the principles of minimal irrigation are important to consider. These techniques are designed to maintain water provision for plants and trees during periods of drought, or reduced rainfall. As stated, this can vary from species to species. Using plants and trees adapted to a particular environment (native species) is advised. Mulches can serve to greatly reduce water loss from soil due to evaporation. Grouping plantings with similar water requirements is also a good idea.
Charts of average evapotranspiration rates (plant and soil water loss) can often be obtained from cooperative extension or the agricultural department. These are used in many states to monitor the irrigation needs of agricultural crops.
(Mulching around trees is a great way to reduce water loss through evaporation, as well as introduce quality organic matter into the soil)
The use of tensiometers (instruments that measure soil moisture) are another tool used to determine water requirements for minimal irrigation programs.
A few methods have even been employed to attempt to increase the water holding capacity of soils especially sandy soils or container soils, by the addition of organic matter but, the effects are short lived because of decomposition. Science continues to explore the use of other soil additives for increasing water holding capacity, but none has gained wide spread use in arboricultural practices. There is also the use of anti-transpirant sprays, which are chemicals applied to the foliage of plants and trees to reduce water loss through the stomata of leaves (transpiration). Studies have shown however that they can sometimes be phytotoxic ( poisonous) to plants and trees.
( Pictured examples of a tensiometer and soil moisture meter )
As mentioned earlier, adequate drainage is an important consideration for successful tree growth. A poorly drained planting site can cause decline of most tree species. There are techniques and methods to assist in the extraction of excess water from the root zone of trees. For instance, of first consideration should be examining and understanding the grade and drainage flow pattern. If the planting site is not yet developed then making adjustments to the grade is the first modification that should be made. Attempts should also be made to avoid the creation of low sunken areas.
( An example of anti transparent chemicals )
( Land grade is an important consideration when planning a landscape ).
( Pictured examples of soaker hoses and a basin irrigation set up )
( Florida red maple tree (Acer saccharum )
( Pond apple tree (Annona glabra ))
( Sweet gum tree( Liquidambar styraciflua )
( Sweetbay magnolia tree (Magnolia virginiana ))
( Bald cypress tree(Taxodium distichum )
( Overcup oak tree(Quercus lyrata )
That aside, the installation of a drainage system should be considered in order to usher excess water from the root zone of plants and trees. These systems consist of what are known as drainage tiles, which are basically large perforated catch basins normally made of plastic, although sometimes concrete or terracotta clay is used. These are connected via a system of pipe work, and can be very effective in transporting excess water and directing it to lower lying areas where it is not a concern.
The pipes should slope away from the planting area at approximately 1/4 inch of fall per linear foot of distance. These systems are normally buried about 3ft deep, but should not be placed below the hard pan level.
Care should be taken to ensure that tree roots are not excessively damaged during installation. If you have questions or concerns regarding irrigation or drainage issues on your property, please feel free to call us. We can assist you in properly reading the landscape, and can determine the best course of action if any to be taken. We can also design and install the most practical, long term irrigation or drainage system to adequately meet your growing needs, and ensure the continued health of all the plants and trees on your property both now and in the future.
( Diagram showing a basic tile drainage system) (i.e. a tree well )
( Picture showing drainage tile installation. )
( Another diagram showing a more complex drainage tile system. )
( American sycamore tree (Platanus occidentalus )
( Bottle brush tree in this case (Callistemon rigidus )
Irrigation and Drainage Solutions
If working on an already developed site, there are limitations to the effectiveness of maintenance practices in controlling drainage. Careful selection is of utmost importance when choosing trees for the adaptation to wet soil conditions. Some good tree choices to consider are; Red maple, (Acer saccharum, Pond apple (Annona glabra), Sweet gum (Liquidambar styraciflua), Sweetbay (Magnolia virginiana), Bald cypress (Taxodium distitchum) and Overcup oak (Quercus lyrata). Other good choices are the american sycamore (Platanus occidentalis) and the bottle brush tree (Callistemon rigidus) (shown). Before purchasing any of these trees however it is important to make sure that they were grown in a low land nursery or setting. It is an interesting fact that trees of the same species perform differently depending on what environment the parent stock originally came from, hence the powerful effect of environment upon genetics.