Air pruning is a rather nebulous term . How would a plant be pruned by air anyway ? Well , first off , the term doesn ’ t refer to clipping leaves . It actually refers to a controlled drying out of root tips to encourage lateral growth in the root zone , resulting in improved growth up top . Perhaps a better term would be “ air-assisted root pruning ”, although , admittedly , it doesn ’ t sound as catchy . That said , the principle of air pruning is a lot like what happens with the green shoots above ground . If you pinch off the growing tip of a plant , it will respond by making all the lower growth bush and branch out considerably more . Usually , two or more fresh growing tips appear at the site where you cut off the original sacrificial shoot . The same thing happens with roots . If you cut the tips off , it stimulates lateral growth further up the root shaft , thus filling the space with lustrous dense roots . ( Quick note : cutting root tips off with a blade can introduce infection to the wound . Air pruning , on the other hand , avoids this .) Left to fend for themselves in a pot , roots don ’ t usually reach full potential . The plant will send out one main tap root , which will hit bottom and circle round endlessly at the bottom of the pot — the wettest place in the rhizosphere with the least available oxygen . This can lead to all kinds of problems in the root zone that will be reflected up top . It ’ s also an inefficient use of space as most of the grow media is unused and takes a long time to fill up . Roots that have been air pruned will fill the entire container , giving the plant maximum efficiency and an enormous surface area to absorb all those yummy nutrients . Drainage will also improve , increasing the amount of oxygen in the root zone and reducing the pooling of water , which in turn reduces the risk of root rot . You will notice faster growth up top , healthier plants , and significantly increased yields . After all , massive roots equal massive blooms . To air prune , you must go against the pervading wisdom about roots — that is , keep ‘ em dark and keep ‘ em moist — and expose their tips . Again , just the tips ; roots don ’ t ever appreciate bright light on them . My favorite method of air pruning is to start early . When a cutting or seedling has rooted , you can transplant it into a three-inch rockwool cube . I prefer the smaller three-inch size as roots can fill the space quicker than the four-inch size , and you will soon transplant the roots to a larger space anyway .
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Perhaps a better term would be “ AIr-assisted root pruning ”,
although , admittedly , it doesn ’ t sound as catchy .”
Then , sit the cube on a metal grill , allowing the air to circulate underneath . You can either make a bench for the grill to sit on or just rest it on top of your planting tray . Top-feed as usual and allow the nutrients to drain freely through the base of the cube . After a few days , you ’ ll see some white roots poke out of the bottom . At this point , some people might panic and race to re-pot the plant to avoid the roots drying out . Don ’ t panic ! Let those roots dangle . They will dry out and die back — which exactly what you want .
Give it a few days and you will see many little root clumps burst through instead of one or two stragglers . Hang tight and let these ones die back , too . Before you know it , the whole base of the cube will be a monstrous carpet of luxuriant white roots . Do not even think about transplanting the cube into a bigger pot until the roots are bursting out of the sides like crazy . Bear in mind that more roots you have in the cube , the faster it will dry out , so adjust your watering schedule accordingly . If you are using soil , it ’ s the same principle . Put your rooted cuttings and soil mix in a cheap cloth or plastic pot that
will allow the roots to grow through and die back . When the roots are totally filling the small pot , it ’ s the perfect time to re-pot into the larger container that the plant will spend the rest of its life in . The roots will colonize the new space vigorously and the plant will grow at an enhanced rate . You can keep this principle going with the larger pot , too , thus maximizing the root growth all the way to harvest .
Personally , I use air pruning on every plant I grow and have only seen beneficial results . Try it yourself ; you won ’ t be disappointed . grow cycle 115