September 15, 2017
When we talk about the importance of newly planted trees and shrubs becoming “established” in the garden, we are referring to the development of a healthy root system. This root system is the basis for the plant’s top growth and long term health. And water is the key ingredient in developing that root system. For the first two years of its life in your garden, the tree and its roots are particularly sensitive to water deficits. As the tree matures, its roots reach deeper into the ground and are able to tap water sources there.
New shrubs and trees will require supplemental watering throughout the first growing season, right up to the onset of winter, and again in the second growing season. Water needs to be applied in the form of a gentle and deep soaking, down to the bottom and around the entire circumference of the root ball. Importantly, plants will require this watering at least once a week, and oftentimes twice a week in order to prevent any part of the root system from drying out.
How much water a plant needs depends on its size. A small shrub will need 2-3 gallons of water each time it is watered. A larger shrub, 3-5 gallons. A small tree will need 5-8 gallons. Mid-sized and larger trees, correspondingly more.
Water can be delivered in several different ways:
- A garden hose turned on at a slow trickle and set near the base of the tree or shrub should be moved around the tree so that the circumference is equally watered.
- If you enjoy the peace and quiet of the garden, holding a watering wand attached to the end of a hose is a pleasant and effective way to water plant material. Allow the water to form a large puddle under the first tree or shrub. Move to a second tree or shrub and form a puddle there. As you are working with the second tree or shrub, the first puddle will be soaking into the soil. Move back and forth between these trees and shrubs 3 or 4 times to ensure a deep soaking.
- Soaker hoses can be placed around the base of trees and shrubs in concentric circles to cover the root mass circumference, or wound in a serpentine pattern up and down a row of newly planted trees and shrubs. They can be set on a timer and left to run for several hours depending on the size of the plant material.
- Traditional sprinkler systems are intended for watering lawns or beds with annuals and perennials. They are not the best way to water new trees and shrubs because they do not allow for sufficiently deep watering. It is recommended that you supplement with any of the methods described above. It is worth noting that systems are available that utilize special drip lines and emitters that allow for longer watering cycles.
Two watering strategies that will not serve your plants well:
- Watering frequently but lightly does not benefit the tree or shrub as it encourages root development at the surface, making the roots particularly vulnerable to drying out in times of water deficit.
- Keeping a plant in soaking wet conditions day after day will deplete the oxygen in the soil, not a good thing for any life form! Hence the need for deep watering followed by a period in which the soil is allowed to dry out.
New England experienced drought conditions in 2015 and 2016. The spring rains of 2017 were certainly welcome and while the official drought designation has been lifted, our trees and shrubs, even established ones, may still be feeling the effects of the drought. Parts of their root systems may have died back and it can take some time for the effect of that to be seen in the top growth. By providing supplemental watering we can encourage new root growth and mitigate the long-term drought damage.
Even as night time temperatures cool and the grass is moist with dew in the morning, it is important to keep up your program of supplemental watering. Scientific data indicates that plants need one inch of rainfall per week throughout their lifetime. While we can hope for a soaking rain every week, it is not something we can rely on, so it falls to us to be good stewards of our landscapes.