Once the other essential requirements of air, sunlight and soil have been met, water is the single most important aspect of a tree’s life.
Let’s talk about watering. Once the other essential requirements of air, sunlight and soil have been met, water is the single most important aspect of a tree’s life. Controlling all aspects of growth, defence and energy production, water is literally the water of life.
Now to get a handle on how water moves in your garden. We need to consider the highly complicated relationship between the lay of the land, soils, rain, downspouts from roofs, additional water and sun exposure. These factors strongly affect how you will need to water in order to maintain vigorous trees. Why? Simply because healthy well-watered trees are usually trouble free. Able to defend themselves from their predators, they look good, and need minimal pruning. What is more important when it comes to care, water is much cheaper and healthier than fertilizers, chemical spraying and injections, and expensive arborist services, all common practices used by many people who don’t maintain the natural vigor of their trees by meeting those trees’ water requirements.
The lay of your land determines how water moves through your garden. If you have a steep section with trees planted near the top, the only way to water properly is from the top down. Usually a soaker hose, a flat hose with evenly spaced pin holes is the best tool. Water is gravity’s slave, and always flows downhill, underground.
Be wary of low lying areas. Look for natural plant growth and use the presence of these plants as indicators of soil moisture levels. In order, moss, horsetails and cattails show wet and progressively wetter soil. These areas that never dry out are not good places for trees.
I have already said a lot about soils; here is the water perspective. Different soil constituents move water at highly variable rates. If the soil has a high content of sand or rocks and cobble, water moves very quickly through it. If the soil is well tilled, loamy, with a healthy percentage of organic material, water will move slower and at about the optimum rate. Heavy clay soils tend to become saturated and move water very slowly. The clay takes up a lot of water and just holds it. Trees planted in clay-based soils, especially in low spots, are easy to drown. These are significant factors in watering.
Rain is a blessing, and in naturally dry areas is the major factor in plant growth. As they say in New Mexico, sky determines. It is a good idea to measure the amount of rain you get and keep a record in a yearly log. Rain water is the best and absorbs nutrients suspended in the atmosphere. It has no chlorine and is free. Whenever possible, downspouts from house and garage should be aimed at trees, probably doubling the amount of rain water they receive
Hand watering, the practice of using a hose and various sprinkler devises, is a guaranteed way to get the water trees need, where and when they need it. You water as required, skipping over rainy times and concentrating on being generous during hot spells. If you have shallow soil, and the temperatures are in the mid to high 20's, the soil can become dry in a week. I like watering tools that simulate the flow of a good steady, soaking rain, not with so much flow that it will cause run-off rather than penetrate the soil. This is why watering with only the hose can be wasteful. A good way to use the hose only is with the flow of the diameter of a pencil, good for deep soaking a specific area.
Irrigation systems can be handy, but they do introduce a level of disconnection from the garden and its soil. Irrigation systems are often set up for many short 20-minute sessions a week. This will keep the turf happy, but little will be left over for the tree roots below. When watering a tree, think of the soil zone you have identified as a water reservoir. With longer, deeper, infrequent watering you fill up the tank and let the trees draw it down for weeks before you fill it up again with the next 3-4 hour watering session.
I have three groups of mature white spruce in my garden. When it has been dry for about three weeks I water each group with a small watering tool that creates a 25-foot circle of rain. I have the tap wide open and let the water soak in for four hours. I do this for each of the three groups, moving the sprinkler into the most advantageous spot. I have followed this practice for years; my trees are healthy, with good annual growth and no insect or disease problems.
A significant amount of water loss is caused by direct sunlight. There is always the sun side and the shade side. During a long 2-3 week dry spell a tree in full sun will use a lot of water every day, performing photosynthesis and transpiration. They need this water to survive. The root system on many trees is so powerful at draining water from the soil, that the size of the root system can be outlined in the turf. A dull brownish color is what the turf looks like inside the circle described by the most active water draining area of the trees root system. Anyone with one of these brown circles underneath their tree will not receive their tree lover’s merit badge.
Another serious loss of water is, of course, large trees, especially spruce, and trees in your neighbor’s property. If you have large trees, mature trees, know that under the grass is a complicated woven fish net of roots throughout your property.
Some trees are just more dominant and efficient at drawing water from a given area of soil than others. If you have a smaller struggling tree, growing within this widely cast net, then baby it. Water on the side farthest away from the greedy large spruce. Trees do not need to be watered all the way around their root circumference. As long as a good section receives water the roots will do their work, and all is well. This is normal and what the root system really does, is find the water, wherever it is. The example from my own garden with my groups of spruce rings true. I water approximately 180 of their 360 degree circle.
And now back to our soil test holes. Some time during the growing season, when it is needed, water a given area of the garden that contains a couple of your test holes. Water for 3 hours, creating a good soaking rain. Wait a couple of days and remove the soil or plugs. How deep did that much water penetrate? Replace the soil or plugs. Leave it alone for another week, remove the soil or plugs and reinspect. Your bare hand is sensitive to water concentrations, and you will quickly sense the change in the soil’s moisture content. Repeat this process for up to four weeks. During this time you have also kept a keen eye on the weather, noting that you have, for example, had three weeks of sunny days in the mid-twenties.
All of this digging, packing, digging will give you insight. This is truly how you learn how water moves in your garden; there will be no more mystery about it. You will quickly learn to feel when your trees need a drink and then give them a good one. A thorough soaking, followed by some weeks for the water to move by evaporation and uptake by trees and other plants, and then another good soak is the cycle for success. It requires one key participant, you. But once done, this process and the knowledge gained will inform you as nothing else can. Perhaps as important will be the natural bond formed between you and your land, you belong there, it is your home. And it has happy trees surrounding it. Welcome home.
All of these watering ideas apply strongly to the trees. Establish this cycle of deep watering and time to use that water. Don’t change how you water other plants with smaller, shallower root systems. Water the turf once every 7-10 days to keep it looking green. Water the perennials once a week as needed.