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Tree Bubblers – When to Cap Them

A residential irrigation system is commonly used to water turf grass and flower beds. Tree bubblers can also be installed in your sprinkler system to water and establish young trees.

Bubblers are small irrigation heads designed to bubble over and flood the ground surface around the tree. The water sinks down into the tree’s root ball (string of roots, including dirt and soil, at the base of the tree), helping to establish a deep root system.

There are a few different types of bubblers available:

Flood Bubblers

Flood bubblers flood the area around them with water. There are two types of flood bubblers, adjustable and non-adjustable. The most common type is the adjustable flood bubbler, which is basically a small water valve with a screw or knob to adjust the amount of water flowing from it. Adjustable bubblers allow you to vary the flow when there are different tree sizes on the same zone, when water is running off the root ball, or when individual trees need more or less water than others of the same size.

Non-adjustable bubblers are, as the name implies, not adjustable.  The water flows at a fixed rate determined by the manufacturer. Common flow rates include: 1/4 GPM (gallons per minute), 1/2 GPM, 1 GPM, and 2 GPM.

Predicting the coverage area the adjustable and non-adjustable bubblers will water is difficult. It depends on the flow rate, how long the bubbler runs, and the soil type.

Stream Bubblers

Stream bubblers can water a larger area by spraying the water 2 to 5 feet from the bubbler.

Micro Bubblers

Micro bubblers have lower flow rates and are often sold as adjustable flow drip emitters with barbs to allow installation on poly drip tubing. They’re called bubblers because they usually have flows over 4 gallons per hour. Most soils can’t absorb this flow rate, and water will pool on the surface.

Bubbler Nozzles

Some sprinkler manufacturers make “bubbler nozzles” that screw onto a spray head, just like other types of spray nozzles. The classic bubbler screws directly onto the end of a 1/2-inch pipe.

Separate Zones

Bubblers for tree irrigation should be on their own valve circuit and run separately from lawn and flower bed zones. The watering frequency and volume requirements for trees vary greatly from other plants. Lawn irrigation, for example, does not provide adequate water for trees. It waters only a few inches of soil which encourages weak surface roots. Additionally, bubblers flow at higher rates than drip emitters — their flow rate is often measured in gallons per minute rather than per hour.

 Bubblers and Tree Planting

  1. Dig a hole three times as wide, but only as deep as the tree’s root ball.
  2. Loosen the root ball and make sure the roots are extending straight out.
  3. Place the tree in the center of the hole, making sure the root flare (part of the trunk at the base of the tree that thickens and meets the top-most root of the root ball) is 1 to 2 inches above ground level. This zone is also called the root collar, root crown, or trunk flare.
  4. Add or remove soil until the tree is sitting at the correct height. Pack down loose soil at the bottom of the hole to prevent the tree from settling.
  5. Build a firm mound (3 or 4 inches high) around the outside edge of the root ball, creating a watering basin (berm) that will help direct water to the roots. Berms are a good idea when the tree is on the far corner of your property, or in a difficult spot to irrigate.
  6. Make sure the bubbler or bubblers are within the berm. If you’re not using a berm, place the bubblers above the root ball.
  7. Give the tree a thorough watering. Fill the berm with 1-1.5 gallons of water per 1 inch of diameter of the tree trunk.
  8. After the water has soaked in, apply a 1-3 inch layer of organic mulch in a circle that extends 4-6 feet around the tree base. Keep the mulch 2-3 inches away from the trunk and root flare. When piled around the root flare, it keeps the bark excessively wet, causing rot and decay. Also, if the layer of mulch around the tree is too deep, it can cause excessive moisture in the root zone, leading to root rot.

Tree Watering With Bubblers

A newly planted tree needs 1-1.5 gallons per 1 inch of diameter each day for the first 1-2 weeks. From 3-12 weeks, water every 2 to 3 days, and after 12 weeks, water weekly. Most of the tree’s roots are still within the root ball for several months after planting, although some are beginning to grow beyond this area. Make sure the bubblers are applying water directly to the root ball.

As the tree grows, move the bubblers back from the base of the trunk. The root system is developing and expanding, and the watering zone should be extended to cover the entire area under the canopy, or drip line (area directly located under the outer circumference of the tree branches).

When and Why to Cap Your Bubblers

After the first year, when the tree is established, the tree bubblers should be capped. They are no longer providing water to the entire root ball, but instead are watering only a small part of it near the trunk. The tree becomes dependent on the irrigation from the bubbler, and the roots don’t reach outwards in search of water well beyond the planting hole.  This creates a very weak root system.

As well, irrigating with tree bubblers after the first year results in a high concentration of water in the area directly around the trunk. This alone leads to crown rot (a disease caused by a soil-borne fungus) but this in combination with mulch piled around the root flare will create ideal conditions for fungus to take hold.

Without a strong and expansive root system, a tree weakened by crown rot can be uprooted and toppled over in a high wind storm.

Tree Watering After the First Year

The roots of an established tree will usually extend well beyond the edge of the canopy. Most are concentrated in the upper 12 to 18 inches of soil, but some anchor roots may reach deeper. Established trees should be watered deeply (at least 10 inches) not only for the entire area under the canopy, but also several feet beyond. Generally, give them 10 gallons of water per one inch in diameter. Check soil moisture with a long screwdriver (8 inches or more). It should be difficult to push into dry soil, and if you can’t push the screwdriver in at least 6 inches, the tree needs watering. In the hottest months of the year trees should be watered at least 4 times a month.

Your irrigation professional can advise you on the best methods to water both your newly planted and established trees.

For all your sprinkler system repair and maintenance needs, call the irrigation experts at Smart Earth Sprinklers at (512) 694-1147.

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