It’s fascinating how plants can adapt over time to the most difficult and unusual of circumstances. Pneumatophores are plants that produce surface roots capable of absorbing and processing oxygen. These root snorkels look like many small sticks emanating from the ground. Without these specialized roots, these plants could not survive in the places they grow: areas where the soil is constantly saturated with water, such as swamps or mangroves.
Beyond nature, there are also man-made root snorkels. They are vertical tubes, usually made of plastic, that are implemented in the hope of adding oxygen into soil that suffers from an overabundance of water or moisture and poor drainage, and thus anaerobic conditions. These tubes are typically perforated to aid the oxygen transfer into the root zone.
However, nearly all man-made root snorkels are passive. That is, air is not forced down into them nor is water pumped away from them. So, the question is, can these passive man-made root snorkels add significant amounts of air or oxygen to the root system?
Studies done on the use of passive evaporation tubes and their ability to aerate the soil found that there is very little evidence of success. Anyone examining the physics involved would come to this same conclusion.
Water will displace air by pushing it upward. Therefore, in a passive root snorkel situation, the only reduction in water content will be that which evaporates at the bottom of the tube. The rate of this evaporation will be less than surface evaporation as there isn’t any air movement down there.
If there is a need to add root zone oxygen for plants growing in an overly moist or compacted and poorly draining soil, there are other options (for example, raised beds and berms—which are essentially the same except one has border walls and the other has gradual slopes—ensure drainage by creating a soil level higher than the surrounding earth). Passive aeration tubes, however, have fundamentally zero to offer for aeration purposes.
But wait; that’s not the end of the story for passive root snorkels. There is another reason for using these perforated tubes, and it’s pretty much opposite of what they are designed to do. Instead of displacing water, passive root snorkels can accelerate the penetration of water deep into the soil as opposed to surface application alone.
Today, more and more landscapes are being irrigated with drip systems. Residential drip systems will generally have two to six different watering stations or zones, while commercial systems usually have more. All the plants within a zone will have water applied for the same length of time.
Consider an example where small flowers that have shallow roots are in the same zone as large shrubs and trees.
An identical watering time for such different plants can present several problems, one of which is watering too shallow for the tree root system. Deep watering creates a deeper root system. This not only provides a stronger anchoring system, protecting nearby hardscapes or home, but encourages the tree to produce fewer surface roots.
Even if we place 10 drip emitters on the tree and only one on the flower, the run time would remain the same and the depth to which the water penetrates would likely remain the same. The extra water would only run deeper in sandy soil, which has a high percolation rate.
Of course, it would be best to place different plant types on different zones or stations, but this isn’t always possible. The expense to continue to add more zones and hence more PVC irrigation tubing to separate the water cycle from one plant type from the other is expensive and troublesome.
Many a homeowner is looking for some easy way around this issue, and this type of situation that deep watering tubes—the very same perforated plastic tubes used as root snorkels—can be so effective.
Two or three of these tubes, typically placed 12-18 inches deep about three feet from the tree trunk, will produce deeper roots in that area. Simply run irrigation into them or, if installed properly, hand-water directly into the tube.
These tubes also work in desert climates where rainfall is not adequate, and in areas where the soil has a high percentage of clay and water penetration is very slow. In geographical areas where rainfall is plentiful, it is rare that deep watering tubes will be necessary. Here, the slow percolation of rainfall travels deeply and establishes those deep roots that are so important to large shrubs and trees.
Just because man-made root snorkels are useless as soil aerators doesn’t mean the technology is useless. These vertical perforated PVC pipes provide rapid deep watering throughout the soil structure.
Watering at least slightly deeper than the existing roots or at least to the depth of the grow pot is the technique for producing maximum root volume in all grow media applications. Indoors or outdoors, deep watering is the way to go.