Success with cuttings depends upon many factors, the most important of which are timing, types, hormones, media, propagating cases, and general culture.
Importance of Timing
Timing, which is probably the most important single factor, is as yet relatively little understood except in purely empirical terms.
We know that cuttings of some varieties of common lilac may root quickly and well if taken in late May, just after flowering, while cuttings taken from the same plants in July may root slowly or not at all.
With such species as the Ghent hybrid azaleas, even a few days’ difference in timing may have an important effect on subsequent rooting.
Environmental Conditions
Since environmental conditions differ markedly from year to year, it is usually impossible to secure the best results merely by following the calendar.
One must have some criteria by which to estimate in terms of potential rooting response.
Most professional propagators rely heavily on the breaking strength or firmness of the stems as a guide to correct timing.
Thus cuttings of Rhododendron obtusum kaempferi, and many other azaleas are said to root best if the basal portions of the stems of the current year’s growth will snap when the stem is bent at right angles.
Since such bending will break all but the most immature growth of early spring, one can easily obtain a promising snap at almost any time of the year.
It is, therefore, necessary to begin frequent sampling of the cuttings a few weeks after flowering.
The cuttings should probably be taken when stem elongation has practically ceased, and a few of the more advanced shoots will snap when bent at right angles.
If one must err, it is better to collect cuttings that are too soft than too firm.
Batches of Cuttings
Forsythia, philadelphus, and beauty bush will probably root best while the stock plants are still growing.
If they are really too soft to root, they will probably wilt excessively and die while there is still time to secure suitable, firmer wood in the same season.
Professionals often have to repeat batches of cuttings to secure a good “catch.”
We not only have to repeat, but we plan to include fairly large numbers in each repetition. Twenty cuttings in each batch is a good basic number for the home gardener.
Types Of Cutting
The type of cutting may be an important factor in successful rooting. Some common types are nodal, in which the basal cut is made just below or through a
Intermodal, in which the basal cut is frequently made about one-half inch above or below a bud.
The basal ring is an entire branch, usually of the current season’s growth, cut through its point of origin on an older branch.
Effect Of The Position Of Cut
Professor L. C. Chadwick of Ohio State University has extensively studied the effect of the position of cut about rooting.
His results indicate that a cut made one-half inch below a node is more effective with a wider variety of woody plants than a cut made in the corresponding position above a node.
He reports that a few genera, including weigela, will root better when the cut is made above a node.
Cuts made at a node were more successful for several genera, including six varieties of cotoneasters.
The writer believes that cuttings of the basal ring type have more possibilities with a wider variety of woody plants than the other common types of cuttings.
Use Of Hormones
The initiation and development of roots are believed to be regulated by hormones and hormone-like substances which are produced in buds and leaves.
When a cutting is removed from a plant, naturally occurring hormones are presumed to accumulate food materials at the cut surface.
This accumulation is usually followed by the production of callus tissue, which tends to seal off and protect the wounded base of the stem. Roots may be formed in this callus or emerge along the stem.
Supplementing the naturally occurring hormones by applying synthetic hormones to the cutting base is frequently advantageous.
Synthetic Hormones
If used judiciously, such applications will often lead to quicker rooting, more abundant roots, and better-rooting percentages.
Synthetic Hormones are particularly effective on hollies and rhododendrons, much less effective and less necessary with viburnums and roses, and usually ineffective with very difficult species, such as mountain laurel.
The efficiency of a powdered hormone preparation seems to be vitally affected by the size of its particles.
Dipping The Cuttings
Dipping moistened stems of cuttings into the original container will almost certainly cause lumping.
Since it is only necessary to coat the cut surface of the stem, it is probably better to spread a thin layer of powder on a sheet of waxed paper.
The cuttings may be easily treated by dipping their basal ends in water, shaking off the excess, and then rubbing them lightly over the powdered paper.
The used paper, including any powder adhering to it, should be discarded. In this way, one can maintain one’s basic supply of hormones in good condition.
Rooting Media
Although coarse sand is the most widely used rooting medium, mixtures of sand and peat moss may be superior.
Sand and peat are usually combined in about equal quantities by volume. Such combinations may result in better rooting of many species, especially ericaceous plants.
The addition of peat moss improves the water-holding capacity of the medium. In recent years, vermiculite has been rather widely used as a substitute for sand.
It is readily available in large or small quantities and deserves consideration. In preparing a cutting bed, the medium should be from three to six inches deep, depending upon the size of the cuttings.
Propagating Cases
Cuttings may be successfully rooted in a wide variety of structures. For example, large propagating establishments use both greenhouses and cold frames.
Whenever possible, cold frames should be situated in sheltered, shady locations. It is desirable to have a variety of covers, including glazed sash, slatted lath, and coarse burlap shades.
Cuttings are sometimes planted in the open ground, where they can be protected with inverted glass jars until they are well rooted.
An aquarium makes a useful miniature greenhouse to root a few cuttings. However, even when a cold frame is available, it may be desirable to plant small lots of cuttings separately in pots or boxes.
In this way, both media and general culture can be more easily varied to suit the requirements of the individual species.
General Culture
Softwood cuttings should be collected and planted as quickly as reasonably possible. They should be planted so that the leaves practically touch each other both in and between the rows.
This will require a somewhat different spacing for large leaves than for small-leaved species.
Depending upon the size of the cuttings, from one to three inches of the stem should be inserted in the medium.
Cuttings should be watered heavily after planting, except in very hot weather, the cold frame or other structure should be closed during the first few days.
During this period, the cuttings should be heavily shaded, especially on sunny days. Cold Frames should be covered with a burlap frame (or equivalent shade) on top of a glazed sash.
On hot days, the burlap’s occasional soaking may help keep the frame cool. However, the cuttings will require frequent light watering during hot weather and some ventilation during the day.
It is desirable to water in the morning or early afternoon when the temperature is usually rising.
The cuttings should go into the night superficially dry, with no free water on the foliage.
After roots have begun to appear, or even before, one should increase the ventilation as rapidly as possible without causing the cuttings to wilt.
After a few weeks, it is usually possible to dispense with the sash and use only the burlap frame.
This may later be put aside for the lath shade so that the cuttings are gradually prepared for planting in protected beds or nursery rows in the open ground.
Late-planted cuttings may be left in a cold frame over Winter if they are adequately protected with a suitable mulch and covered with a combination of sash and lath shade.
44659 by Richard H. Fillmore