Plant Propagation: Division Method
Division is the simplest and most obvious method of increase, particularly when it is not possible or wise to propagate by seeds, because it is only necessary to have a shoot or young growth with roots attached in order to form another plant that will be exactly the same as the parent. The method requires a number or mass of shoots or buds growing together which can be pulled apart or severed with a knife to form individual portions, with roots or rudiments and a crown, that will grow on into complete new plants. Plants which grow from a single stem or crown cannot be propagated in this way. Most plants which have a fibrous root stock, such as Michaelmas daisies, phlox, heleniums and solidago (golden rod), are readily increased by division. But the method is not always so easy with other plants.
The division of most plants is carried out during early spring when growth is active, and it is only necessary to retain sufficient rhizome or underground stem to supply the immediate needs of the divided portion until it has rooted and is established.
Shrubby plants can be divided only if they have a compact habit and produce new growth by branching or making suckers from below ground. Examples of such shrubs are Kerria japonica,(St. John’s wort), Rhus typhina (sumach), vinca (periwinkle), ericas or heaths and some spiraeas.
Other classes of plants can be increased by division, although more skill may be required for success. They are:
Plants with underground stems or rhizomatous roots that grow on or just below the surface of the, such as German irises, Solomon’s seal, obedient plant (physostegia), cape gooseberry or Chinese lantern (physalis) and the bee balm (monarda). When of this type, select the strong-growing portions from the outside of the clump or group and discard the central portions which are old and worn out. Divide and replant soon after the flowering is over — July is generally the best time. In this class of iris, the new growth is formed at the end of the rhizome, or swollen, creeping stem. It should be removed from the parent plant by cutting with a strong knife about 2 or 3 in. back from the growth. This will provide a section of rhizome with roots attached which, when planted horizontally and just below soil level, will allow for the quick establishment of the new plant. The modern varieties of the bearded and German irises are divided every second year so that strong growth and fine flowers are maintained.
PLANTS WITH WOODY CROWNS AND GROWTH BUDS
Of thewith a compact semi-woody crown from which numerous growth buds arise, the lupin and are perhaps the best-known examples. Division needs to be done carefully in the early spring if it is to be successful.
Lift the parent crown and shake it clear of the soil, if necessary removing the soil by washing the crown in a bucket of water. It is then easier to divide sections from the crown, with buds or shoots attached. Plant the divided portions separately, or first establish them in pots, and then plant out later after a good root action has been formed.
Although division of this class of herbaceous plant can be successful, modern varieties of lupins andare more often propagated by made from individual shoots and inserted during spring. If the shoots are taken off when they are about 3 in. long they will root easily in pots or boxes of sandy soil placed in a frame. They will also root in the open ground in a semi-shaded spot, but it is better and quicker to give them the protection of a frame or cloche.
Tuberous-rooted plants, such as paeonies, need special treatment and careful handling when being divided.
Divide paeonies during the early autumn. The eyes or growth buds can easily be seen on the tubers, and each division should consist of an eye and a tuber. If large numbers of a certain variety are needed, plant them out in well-prepared soil in a nursery bed with the eye about 2 in. below the soil level. But if only a doubling or trebling of stock is required, lift an established crown and divide it into several portions by using two hand forks back to back pushed well between the roots. Then gently lever them apart to avoid snapping too many rootlets.
Paeonies unfortunately dislike root disturbance and several years will often elapse before the divided crowns will flower freely, so do not dig them up unless it is necessary and new or increased stock is required.
The potato is another example of a tuberous plant which can be divided by being cut into pieces with an eye or bud attached.
Few beginners propagate tuberous-rootedby division of the tuber, although the method is simple if the tubers are placed in a greenhouse or warm frame to start them into growth before dividing them. Put them in shallow boxes, barely cover them with peat-moss or sandy leaf-soil, and growth buds will appear, producing stout, strong shoots. It is then easy to see where to cut the tuber into portions, each with growth buds attached. Dip the portions into powdered charcoal to dry up the cut surfaces, and then either pot them singly or space them out in boxes to grow on. The multiflora class of tuberous , popular as a summer bedding plant, forms large irregularly shaped tubers that will produce many growing shoots, so that many plants can be obtained by dividing the tubers.
Another large and varied group of plants, which includes, , crocuses, and the bulbous irises, produce their annual growth and flowers from a bulb or corm. These plants do produce seeds and can be propagated by them, but often three to five years elapse before the reach flowering size. This group has, however, an alternative means of increase by the production of offsets. These are complete but smaller new plants that are produced alongside and attached to the parent bulb, the number of offsets produced varying with different species. Daffodils have what is termed a ‘mother bulb’; this is one large bulb with two or three offsets which produce a number of shoots and flowers. The offsets on daffodils, tulips and other bulbs can be removed and planted separately to form larger bulbs, but only the larger of them will flower in the first year.
Suckers are shoots that grow from the roots of some plants and usually appear round the base of the plant. In some cases they are a nuisance: for instance, roses and grafted trees of lilac, plum and apple. And, amongst large trees, the poplar and elm, are notorious for producing unwanted suckers. But in some other plants sucker growths provide a quick and sure means of reproduction. A good example is the raspberry, which produces sucker growths that often appear several feet away from the parent plant. The growths can be severed in the autumn and lifted with roots attached.
The stag’s horn sumach (Rhus typhina), spiraeas and some roses, such as Rosa rugosa, the Japanese rose, are easily increased by suckers.
The use of suckers for increasing stock should be exercised with discretion, because certain grafted trees produce sucker growth from the root stock and these suckers ultimately produce plants like the stock. Suckers of the peach, for example, which are often grafted on to a plum rootstock, would produce plum, and suckers of pears which are grafted on to the quince would produce quince.