Young trees need a lot of water in the first few years after they are planted in order to grow properly and develop their roots. And as a result of climate change and the associated more frequent and longer dry periods, even older trees should be supported in their water supply from time to time to avoid damage caused by drought. For this purpose, special systems and tools for tree irrigation are offered. I will then introduce these and also explain what alternatives can be done at no extra cost.

Especially with trees, the need for additional irrigation seems illogical at first glance: After all, trees in the forest survive without being watered by humans. However, these have very different conditions than trees standing alone, as the forest provides shade on the one hand and the plants in the forest are connected to one another via a fine network of fungal threads and exchange water and nutrients via this. This network compensates for deficiencies and supports young trees in their growth. Trees outside of a forest, on the other hand, are on their own and are more often exposed to drought stress. This can manifest itself in deficiency symptoms or poor growth of the tree, but in the worst case it can also lead to the death of the tree.

Newly planted trees should be watered thoroughly once or twice a week in the first year after planting. As they get older and the roots reach deeper, the tree only needs additional water less often, e.g. only once a month, until the need for additional watering is finally limited to longer periods of heat and drought. Exceptions to the rule can be very close plantings or plantings on heavily compacted soil. In these cases, permanent watering may be necessary.

As with lawns and hedges, the same applies to trees: do not water a little every day, but water less frequently and a lot of water at once so that it can seep deep into the root area and the layer of soil remains moist for a longer period. An amount of water of at least 20 gallons or more is ideal here.

Below is an introduction to the most popular methods for watering trees:

Irrigation with tree watering bag

These are the large sacks that you can see attached to almost every tree if you walk carefully through a city. You might assume that the sack protects the tree trunk from cold or damage, but in fact it is used for watering. The name for this is not always consistent, and the terms irrigation sack or irrigation bag are sometimes used.

Installing such a bag is very simple: depending on the model, the bag is simply wrapped around the tree trunk and then closed with a zip or tied to the tree trunk. This way, the empty bag cannot fly away and it cannot fall over when full. For larger trees, several tree watering bags can be lined up next to one another.

The tree watering bag is wrapped around the tree trunk and then the zipper is closed

The tree watering bag is double-coated so that there is a hollow space between the two layers. The water is filled into this hollow space through a filling opening; a standard tree watering bag holds 20 gallons of water. The easiest way to fill it is with a garden hose.

Filling is done through an opening in the inside pocket of the bag

Once filled, the water is slowly and evenly released into the ground. This is ensured by small irrigation holes in the bottom of the bag, through which the water drips onto the soil and flows into the root area beneath the tree watering bag. Depending on the manufacturer and the size of the irrigation holes, it takes 6 to 11 hours for the tree watering bag to be completely empty. The bag also reduces evaporation because it covers the area of ​​the ground where the water is released.

A tree watering bag can be removed from the tree at any time and used elsewhere, e.g. when the tree is old enough and no longer needs additional water.

Why are tree watering bags used?

And why not just water the tree directly with a hose instead? If you were to water such a large amount of water at once, the soil around the tree would not be able to absorb it so abruptly and a large part of the water would run past the tree’s root area. So you would have to spread the amount of water over a longer period of time, which is cumbersome and time-consuming, or accept that a lot of water would be wasted unnecessarily. The tree watering bag, on the other hand, can be filled quickly, saving time, and micro-irrigation spread over many hours is particularly effective because the root area has enough time to completely absorb the water.

You can buy a tree watering bag for around $15 to $20.

Irrigation with drainage pipe

With this form of irrigation, a sufficiently long drainage pipe ending at the surface of the earth is installed next to the newly planted tree in order to be able to supply the root area with water directly from above. To ensure that the water is not only released at the end of the pipe but over the entire length of the pipe, the pipe must have holes on the side. In this way, it is also very easy to bring fertilizer directly to the roots.

Unlike the tree watering bag described above, the drainage pipe remains permanently in the ground. For older trees, it can still be used for occasional watering during dry periods.

Fully automatic root zone irrigation

Irrigation with a root zone watering system is a further development of the previously described method. Compared to the two previously described methods, this has the advantage that irrigation is possible even when you are away, e.g. on vacation, because it can be fully automated.

Root zone irrigation system pipes in different sizes (photo courtesy of Hunter Industries Incorporated)

Such a root zone watering system is in principle very similar to a drainage pipe, but consists of a straight cylinder made of solid, non-bendable material. The cylinder is perforated throughout, like a sieve. It is open on the underside and a lid with ventilation slots is placed on top. This allows the system to be easily accessed from above and also serves to protect the technology from vandalism or accidental damage. The ventilation slots in the lid are intended to allow air to reach the roots from above, which also has a positive effect on the tree.

Root zone irrigation system installed (photo courtesy of Hunter Industries Incorporated)

Unlike with drainage pipes, the water supply to the root zone watering system is not from above by pouring water into the pipe, but the water is fed underground, virtually invisible from above, to the system using an irrigation pipeline. For this purpose, a swing joint connector is attached to the dylinder of the root zone irrigation system, which can be used to connect it to a pipeline very flexibly. I explain in detail how to build such a pipeline on the planning and on the installing page of this website.

Inside the root zone irrigation cylinder there is usually a pressure-regulating bubbler that reduces the water pressure to the required level and from which the water flows out slowly in 360 degrees. The water runs along the sieve on all sides and reaches the root area through the sieve holes.

The RZWS root zone watering system from Hunter, for example, releases between 15 and 30 gallons of water per hour, depending on the model. The bubbler in the cylinder can be exchanged, i.e. replaced with a bubbler with more or less gallon output per hour if required. This can be done very easily from above by removing the lid. The Hunter RZWS is fitted with Hunter PCB bubblers, which are available in 15 and 30 gallons, as well as 60 and 120 gallons per hour. However, faster irrigation usually makes no sense in practice, as slow, gentle irrigation is ideal for the tree. This is also a significant advantage over the drainage pipe method described above, in which the water is poured into the pipe in large quantities in one go.

For each tree, one root zone watering system is buried in the ground to the left and right of the tree. For larger trees, more may be useful. For new plantings, the cylinders are placed adjacent to the tree’s root ball; for existing trees, they are placed halfway between the tree trunk and the outermost edge of the tree crown.

Root zone watering systems are available in lengths from 10 to 35 inches. As an alternative to the Hunter RZWS system, the Rain Bird RWS system is also available, which works in almost the same way. I couldn’t find any other suppliers in my research.

Below are the root zone watering systems from Hunter and Rain Bird on Amazon
(Be careful when buying: some sales offers only include the pipe without any technical internals)

Rain Bird RWS Hunter RZWS

Watering ring/watering rim

This is usually a ring-shaped enclosure that is mounted around the tree trunk. High-quality watering rings hold up to 30 or more gallons of water and are made of sturdy material to prevent the relatively high ring (up to 12 inches high and more) from deforming due to the water pushing outwards.

The application is simple: the watering ring is filled with water, the water cannot flow away through the border and thus flows into the soil in the root area. And this happens relatively abruptly; a slow, continuous release like with a tree bag or root zone irrigation system cannot be achieved with this method. Some watering rings show the water level in the ring using markings for better orientation.

You can of course also build such a watering ring yourself, but you should ensure that it is sufficiently stable – especially if the ring is to contain larger amounts of water and is free-standing. Conventional lawn edging or other softer materials can only be used if the watering ring is sunk into the ground and is thus supported laterally by the soil.

Free tree watering methods

Without spending any money, you can help yourself with a watering rim made of piled up earth or a watering trough:

Watering rim made of earth

Instead of buying a ready-made watering ring, you simply pile up an earthen wall around the tree. This won’t last forever, but it does serve its purpose of preventing the water from running out of the root area.

How to make a watering rim out of soil

Watering trough

In principle the same as before, only now no side border is built up, but instead the circle around the root area is dug out a few inches deep so that the water remains in this trough when watering.