Q. I just read about air pruning of roots in potted
plants using either fabric pots or drilling holes in pots and lining with
landscape fabric. Supposedly, air
pruning keeps the roots in “check” so that they do not outgrow the
pot. The idea sounds logical, but with
our extreme heat and hot winds, could this work in Vegas? I know that pots kept
in the sun will overheat and kill roots.
If the pot is large enough, would it only kill the outer roots, similar
to the action of air pruning?
plants using either fabric pots or drilling holes in pots and lining with
landscape fabric. Supposedly, air
pruning keeps the roots in “check” so that they do not outgrow the
pot. The idea sounds logical, but with
our extreme heat and hot winds, could this work in Vegas? I know that pots kept
in the sun will overheat and kill roots.
If the pot is large enough, would it only kill the outer roots, similar
to the action of air pruning?
I have some large pots and as I get older, it is going to
be very hard pulling the plant, cutting the roots and re-potting with fresh
compost. Any thoughts would be appreciated.
be very hard pulling the plant, cutting the roots and re-potting with fresh
compost. Any thoughts would be appreciated.
A. Air pruning is a form of root pruning. There is nothing new about root pruning. Root pruning is used in growing bonsai to help keep the plants small and reduce the amount of top growth. Root pruning is used in nursery production to restrict the size of the roots and increase the survival of field grown trees that will be harvested and sold as bare root, containerized or balled and burlaped.
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| Machines like these are used in commercial nurseries for root pruning young trees before they are harvested as bare root or transferred into containers. Root pruning concentrates the roots close to the plant so they can be transplanted with a higher percentage of success. |
You can use air pruning in our hot desert with high
light intensities if you regulate the solar radiation heating the soils inside
the containers during summer months.
Container plants should be repotted every 2 to 3 years as
you know. You might be able to skip the part about cutting off some of the
older roots but if you do not replenish about one third of the soil it will
eventually be like growing a plant in sand or hydroponics. You might be able to
use compost tea as a soil drench for the plant in the container. That, and the
addition of a good fertilizer plus micronutrients, might get you by.
you know. You might be able to skip the part about cutting off some of the
older roots but if you do not replenish about one third of the soil it will
eventually be like growing a plant in sand or hydroponics. You might be able to
use compost tea as a soil drench for the plant in the container. That, and the
addition of a good fertilizer plus micronutrients, might get you by.
 |
| Hopefully good management of plant root systems can help prevent girdling or circling roots, a huge problem in the nursery industry and passed on to the homeowner and not discovered for many years later. |
Just as you stated, air pruning is allowing tender roots
to come in contact with dry air thus killing them. This is usually a greenhouse
technique.
to come in contact with dry air thus killing them. This is usually a greenhouse
technique.
In the nursery trade we used to use copper sulfate to
control plant roots. When plant roots in they did a space treated with copper
sulfate, they died back from copper poisoning. Copper did not travel back inside
the plant but stayed localized where it came in contact with roots. This was
sometimes used in what is called pot-in=pot culture or “double potting” where a
plant is grown in a container and that container put inside of another
container that had a shallow layer of gravel at the bottom to prevent the two
of them from lodging.
control plant roots. When plant roots in they did a space treated with copper
sulfate, they died back from copper poisoning. Copper did not travel back inside
the plant but stayed localized where it came in contact with roots. This was
sometimes used in what is called pot-in=pot culture or “double potting” where a
plant is grown in a container and that container put inside of another
container that had a shallow layer of gravel at the bottom to prevent the two
of them from lodging.
 |
| We used pot-in-pot culture when growing ornamental trees for a research project in the 1990s. The container inside of the container that was buried into the ground helped keep the container soil cool. This reduced the risk of high temperatures in the soil surrounding the roots and root damage. |
 |
| Growing plants in black nursery containers in the hot Mojave Desert runs the risk of root damage due to high soil temperatures. |
The outside pot was buried in the ground nearly up to its
rim. The outer pot acted as a “sleeve” for the inner pot and helped
prevent potted plants from blowing over in the wind. This was a big problem in
the nursery trade and required many man-hours to “right” the plant
after a wind. If copper sulfate was not
used on the gravel between plants or the inner pot was not twisted every couple
of weeks during the growing season, the roots from the plant in the inner pot
would grow through the gravel and through the second pot into the ground and
the plant would be ruined.
Air pruning is similar but without the harsh chemicals.
When plants are grown in black nursery containers in full sun, one half to two
thirds of the root system of that plant can be killed during summer months due
to high soil temperatures. Surface temperatures of black nursery containers can
reach 170° F in direct sunlight in just minutes. High temperatures spread
through the container soil on the sides facing the sun. Damage is worse if the
soils are dry.
When plants are grown in black nursery containers in full sun, one half to two
thirds of the root system of that plant can be killed during summer months due
to high soil temperatures. Surface temperatures of black nursery containers can
reach 170° F in direct sunlight in just minutes. High temperatures spread
through the container soil on the sides facing the sun. Damage is worse if the
soils are dry.
What to do?
• Paint
nursery containers white. This helps to lower the surface temperature 6 to 10°
F.
nursery containers white. This helps to lower the surface temperature 6 to 10°
F.
• Keep
nursery containers shaded during summer months by double potting them, placing
a son barrier on the outside of the container on the South and West sides
nursery containers shaded during summer months by double potting them, placing
a son barrier on the outside of the container on the South and West sides
• Grow
nursery plants in partial shade; 30 to 40% shade is best.
nursery plants in partial shade; 30 to 40% shade is best.
• Water
nursery plants just prior to the heat of the day so that soils are moist. Moist
soils do not gain heat as much or as rapidly as drier soils.
nursery plants just prior to the heat of the day so that soils are moist. Moist
soils do not gain heat as much or as rapidly as drier soils.