Air Layering

Making air layers on woody plants toinduce rooting is a practice that is centuries old.Generations of Chinese did it, and undoubtedlyit was introduced into America by the earliersettlers. Until comparatively recently themethod has been used chiefly in the greenhouse.It consisted of scarifying the stem of a plantand wrapping moist moss (or soil) around thatinjured plant part. If the wrapping material waskept moist continually, rooting often occurred.The difficulty came in keeping the wrappingmaterial moist. Rubber or paper wrappings didnot prove satisfactory, and watering of thewrapping would frequently have to be donedaily and even several times a day in a hotgreenhouse. This continual care was frequentlymore bother than it was worth.

Now, with the use of polyethylene film, airlayering is a method which every home ownercan use to increase his plants. The propertiesof this film are such that it is indispensable formany horticultural purposes. Although it allowsample gaseous exchange, it does not permit thefree transmission of water or water vapor, whichis the reason why it has so many uses in keepingplant materials alive.

The making of the air layer itself is verysimple. A longitudinal cut of about 2 in. is madeon the young twig, the cut going nearly to thecenter of the twig. (An adaptation of this is toremove a complete circle of bark 4 in. widearound the stem.) Then both cut surfaces aredusted with some hormone rooting powderwhich may (or may not) aid in the rooting.Hormodin #3 has been used, but undoubtedlyother materials are just as good. Moist sphag-num moss‚Äîabout a handful‚Äîis packedbetween the cut surfaces and then all aroundthe entire cut, fully covering it, then tied in place.Polyethylene film is wrapped carefully andtightly about it, then tied top and bottom.Rubber bands used in grafting have notproved satisfactory for tying, but ScotchElectrical Tape # 33 has proved most satis-factory.

The wrapping and tying of the film should be done in such a way that the moss is wellcontained and that no opening in the film is leftfor the evaporation of the moisture from themoss.

The overlap of the film wrapping should beon the underside of the air layer so that rain-water will not seep in. Also, in taping the topend of the wrap, the tape should be started onthe bare twig and gradually spiral down tocompletely close the top end of the wrap inorder that rainwater will not seep down thetwig and into the moss inside. Many air layersmay have failed to root because this was notdone, since water seeping into the moss packingwill push out much of the air and create a soggycondition decidedly unfavorable to rooting. Ifproperly done, the air layer will remain moistfor months (some remain moist for a year) androoting may take place in a few months’ time.This is all there is to the operation. The timeof year when it is done, the size of twig used,the amount of hormone powder, the amount ofmoisture in the moss and the rooting tendenciesof the species used are variables with which oneworks to achieve proper rooting. Air layersmay be made in early spring on wood that isdormant, and again in June and July on twigsthat grew during the current year. Many plantsare propagated from both “hardwood” ordormant cuttings and “softwood” cuttingsmade of wood grown the current year; othersmay root better from just one of these types ofcuttings. Consequently one would expect thatthe time when these layers are applied with bestresults might well vary with the species.

Twigs have been rooted that were ftc. india., although usually one might expectnormal rooting from the twigs about the size ofa lead pencil. Because so very little moisturepasses through the film, one should be extremely careful not to have too much moisturein the sphagnum moss at the time it is appliedabout the cut. The moss should be squeezedprior to application so that it will be moist‚Äînotwet.

Certain plants, such as forsythias, privets,dogwoods and yew, root easily and for theseair layering is one method which can be used.In addition, certain of the plants which are hardto root respond to this teethed. Some years agoexperiments in rooting plants by air layeringwere carried out at the Arnold Arboretum.These experiments showed that in many casesair layering, applied early in the spring to plantsgrowing out-of-doors, is an excellent andversatile method of plant propagation whichmay be used by persons who do not haveproper greenhouse facilities for the more com-mon methods of grafting or budding indoors.It must be admitted, however, that an equalnumber of plants used in the experiments failedto root. Hence the process apparently cannotbe applied with t00% success to all woodyplants. Also, the matter of cutting off therooted layer and establishing it in soil as anindependent plant is not always a successfuloperation. Many times roots are formed by theair layer process, but when the layered branchis cut from the parent plant the roots fail tobecome established in the soil and the youngplant dies. To overcome this, the severingoperation might be done over a period of time,or soil might be packed around the rootedlayer, delaying the cutting from the parent plantuntil after the feeding roots have permeated thesoil.

In any event, air layering is a simple andpractical process, offering to the interestedgardener a means by which he can asexuallypropagate a few woody plants without the useof a hot bed or greenhouse.

Some plants which rooted successfully by theair layer method are: