Pinching Shoots.
All plants grow, and bonsai are no exception. In the height of summer, as little as a week is long enough for a small bonsai to become overgrown and scruffy.
Bonsai shouldn’t just be clipped like a hedge. This will cause over-dense outer foliage and all the valuable inner shoots will die through lack of light. You would then be forced to prune hard and redevelop all the twigs again.
Bonsai must be kept in shape by regular and careful pinching of all the growing tips throughout the growing season – see some examples here in the gallery at bonsai pictures. Pinching is the generic term for this operation, although sometimes you will need to resort to sharp shears, while at other times tweezers will make things easier.
In addition to keeping the tree in shape, regular pinching will achieve three further objectives:
1 It allows light and air to reach the inner parts of the tree, enabling the weak inner shoots to grow more strongly, and stimulating dormant and new adventitious buds to grow. This is crucially important in the long term, because you will eventually need to remove larger areas of congested twigs and replace them with the new growth your pinching has stimulated.
2 It prevents the intern odes (the length of shoot between leaves) becoming too long.
Unless branches are hard-pruned (see page 26), they can only ramify (fork) at an internode. Long internodes mean coarse ramification, which results in a dumpy-looking tree with tufts of foliage at the ends of long branches – not a pleasant sight!
3 Pinching increases ramification. Removing the growing tip of a shoot cuts off the supply of hormones (auxins) produced in the tip.
Deciduous or broadleaved trees.
Each time you pinch the tip of a growing shoot on a deciduous tree, two or more smaller, finer shoots will sprout from axils of remaining leaves – and you have two shoots where there was only one. If you pinch twice in the season, then you will have four. At the end of the second year there will be 16, after three years 64, and so on.
Clearly, this process can’t continue for ever, otherwise the tree would become so dense that it would probably stifle itself if it didn’t take drastic action. This drastic action would consist of shedding branches and throwing out new growth from the base of the trunk.
The increased ramification produced by pinching must be balanced by thinning and rationalisation of the outer areas during maintenance pruning in late winter.
How to pinch deciduous or broadleaved trees.
If you’re still developing branches, wait until the shoots have three or four internodes and then pinch back to the first internode on opposite-leaved trees such as maples, or to the second internode on alternate-leaved trees, such as elms.
If your tree is already well established and has a pleasing shape, you need to be much more disciplined. Watch the buds as they open. The first leaf (or pair of leaves) emerges and at the base of the stem is the tiny bud that contains the next leaf or pair of leaves. The idea is to pluck out this bud as soon as it is big enough to be seen. This is where a pair of tweezers comes in handy.
You don’t have to pinch every shoot at one sitting because the buds don’t all open at once, but always work over the whole tree every time you pinch. Weak shoots, or those you want to develop further, should be allowed to grow longer and should retain more leaves after pinching.
Conifers.
Conifers react rather differently from broadleaved trees, even though the result is the same.
They don’t have buds at every leaf axil – there are so many needles or scales clothing the shoots that it would be ridiculous. Some lateral buds do exist on the shoots, but they are in predetermined locations. Moreover, each conifer species reacts in its own individual way to pinching.
Pines.
Pines are unique insofar as they rarely have preexisting lateral buds on shoots. They are also unique in that they are genetically programmed to have only one flush of growth a year. These two factors share a common cause. Pines are late to begin growth, their shoots take longerto mature, and their buds take a lot longer to become ready to sprout.
When you pinch a pine shoot – or candle as it is known – buds form around the point where the shoot is severed. This is great news, because it means you can shorten a shoot to precisely where you want it to fork. New buds will also appear on the previous year’s growth and, if you’re lucky and the tree is healthy, on even older wood.
How to pinch pines.
Pine buds don’t open in quite the same way as those on other trees. They extend into candles, with the tiny embryonic needles pressed flat to the stem, held in place by a papery sheath. As the candles continue to lengthen, they slowly mature, and the needles begin to pull away from the central shoot. Now is the time to start thinking about pinching.
If you need to induce buds on older growth, you should allow the candles to extend and the needles to peel away until they are standing at an angle of about 45 degrees from the shoot.
Then cut the entire shoot off, leaving just a half dozen or so needles at the base (you will need sharp shears for this). New buds will form on older growth during the autumn and winter, ready for next spring.
If you want to develop ramification, wait until the needles are just beginning to peel away and are standing at about 15 degrees from the shoot. Then pinch back to the point where you want the shoot to fork. New buds will form at the severed end of the shoot.
If your bonsai pine is already established and you want to retain and refme its form, you should attack earlier. The ideal time is just as the papery sheath begins to fall away – the shoots will still be short and soft, and the needles will only just be discernible. Then new buds will form at the severed end of the shoot and around its base. Some will also appear on older wood.
Pinching new growth.
Pines Wait until the developing ‘candles’ are long enough to handle, and break them by bending and twisting at the same time.
Junipers.
Junipers can have either needle or scale foliage, but whichever is the case, about one-third of the leaves will have tiny buds in their axils.
New shoot generation is usually prolific.
Junipers continue growing steadily from spring until well into autumn. If you keep a juniper in a cool greenhouse or conservatory during winter, it will grow all year round.
How to pinch junipers.
Pinching junipers is really easy in one respect. They have such short internodes that the preexisting buds, although few in number compared to the number of leaves, are very close together and itching to sprout.
In another respect junipers are hard work, because they are continuously growing and pinching becomes a weekly routine.
The technique, though, is simple. Just grasp a fan of shoots between thumb and fmger with one hand, and pull off the tips with the other.
Every so often you’ll need to use the point of your shears to cut out the plump, vigorous shoots from the centres of the foliage clusters, so that the younger, fresher shoots have space to grow.
Flat-needle conifers.
Yew, hemlock, larch, some cedars Like junipers, most flat-needle conifers have bUds at about one-third of the leafaxils. Many, though, are capable of generating adventitious bUds on older growth as well in axils that didn’t OGiginally have buds. At one end of the scale, larch almost never bud on old wood, whereas yew do this so prolifically that it can become a realmuisance.
How to pinch flat-needle conifers.
On developing trees, allow shoots to grow until they are almost as dark in colour as the old foliage, then cut back to roughly the point where you want a fork. There are bound to be some viable buds in the near vicinity of the severance point, even if you can’t see them.
On established trees, pinch back hard when the shoots are about 25-30 mm long. Leave three or four needles – no more. Within a few weeks, a new crop of fmer, neater shoots will sprout from all over the place.
Sharp-needle conifers.
Spruce, some cedars Species in this category have some pre-formed buds in leafaxils, but fewer than with flatneedle species. What buds do exist are widely spaced and sprout at right angles to the parent shoot, making for a very untidy foliage mass.
These trees need to be approached in a special way, using a cycle of removal and re-growth.
If you shorten a shoot to below the first lateral bud, so there are no more buds remaining on that shoot (which you will have to do to keep the tree in trim), no new buds will form and the shoot will abort during the following year. This isn’t so much of a problem as it might sound.
New buds will form at the base of the shoot and on older wood. The following spring, the aborted shoots are cut out completely and a new crop of shorter shoots emerges. These may be so short that they don’t need pinching.
When the buds at the tips of these shoots sprout during the third spring, then the cycle will be repeated.
How to pinch sharp-needle conifers.
Since the pinched shoots will abort next year, there’s nothing to be gained by leaving them so long that the tree looks untidy, regardless of whether your tree is established or still in the ramification process. The difference is in the timing.
- Pinching new growth
Spruce.
The shoots emerge like tiny green shaving brushes. As soon as they are big enough to handle, pull out the tips by hand, leaving about a third behind.
To increase ramification, allow the shoot to mature, then remove it completely. Masses of new buds will form at the shoot base and on old wood.
To refme and maintain, pinch out the shoots as soon as they are large enough to handle with tweezers. Leave just a rosette of needles about three layers thick – say, no more than a dozen. As you work over the tree, cut out aUlast year’s pinched shoots, which by now will be looking a little sad. Healthy trees may push out a second flush of growth later in the summer. These shoots will be beautifully small and fine, and will probably not need pinching.
