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6 Pruning Your Hibiscus

The Chinese hibiscus is an evergreen shrub that would, if conditions were suitable, keep growing all year. Evergreen shrubs are treated differently from those that are deciduous. They may be pruned at any time of the year to control the growth.

Why Prune?

The object of pruning is to modify the growth of the plant to fit the space in the garden, but more importantly to produce new wood for better flowering. The more vigorous and healthy the growth is, the larger and better the flowers. After a year or more under good fertiliser practices, the average hibiscus plant has produced a large amount of wood or branches. Often the plant has many sprawling branches that produce few flowers, or one or more verticals that spoil the look or shape of the plant. We prune to obtain a plant of the desired shape, to remove dead and weak growth, and to encourage the development of strong new growth where we want it.

Equipment Needed

First, make sure that you have clean sharp and adequate tools for the job: a good sharp knife for small wood, a pair of sharp pruning secateurs (spend the money for a good pair and throw the old ones away), a pair of sharp lopping shears for cuts up to 2.5. cm (1 in), a sharp pruning saw for anything larger, and a can of plant pruning paint, grafting tar or grafting wax.

Some Hints on Sharpening your Pruning Tools

A sharp file and a good quality stone can help keep your tools sharp. Some tools can be sharpened or touched up with abrasive paper held flat on a solid surface and used like a whetstone. The cardinal rule of tool sharpening is to retain the original bevel of the blade edge. This bevel was carefully engineered for maximum durability and easy cutting, and changing it causes problems. For instance, tools that cut with a slicing action and are not exposed to nicking injuries are ground with a long, thin edge. Examples include pruning shears and lopping shears (see line drawings). Shear blades cut better if the grinding or filing marks run at right angles to the cutting edge, so that each blade under the microscope would resemble a toothed saw. These blades must be filed, ground, or whetted on one side only. To remove metal on the flat side is to ruin the blade. The two cutting edges of a shear should kiss together continuously as the blades come together.

Most secateurs and shears have bevels on only one side of the blade. An exception is the anvil type pruning shear (see line drawings) which is ground to a slender taper on both sides because it is called upon to cut across the wood grain. This is one of the trickiest tools to sharpen. The edge must be kept absolutely parallel with the face of the brass anvil that helps make the cut. If too much metal is removed, the blade and anvil will no longer come together properly and the cut cannot be completed. This blade should be kept off the power grinder and sharpened sparingly with oilstone only.

How to Prune

Pruning is not a black and mystic art. It is simple when you know how and have the right tools. The important points to remember are:

  Prune at the right time.
  Prune to an outward pointing bud.
  Cut away all dead, criss-crossing and weak-looking wood.
  Make all cuts clean and smooth.
  Leave no stubs to cause decay. (See line drawings).

Note that when using pruning shears the thicker, non cutting blade is in contact with the unwanted part of the stem, and the sharpened edge is toward the plant (see diagram).

Examine the plant and cut off all dead, diseased or injured wood, cutting well down into live green wood, and making the cut at a slight slant to shed water. All cuts a centimetre or more (over in) should be treated with pruning tar. This coats the cut to prevent infection and promotes healing over without decay. Never leave a stub above a bud or branch. Always prune close because stubs will decay and cause trouble.

Then remove small twigs and branches that cross and grow toward the inside of the plant. This is to allow light and air to penetrate to the interior of the plant which will reduce fungus and insect problems. Locate the eyes or buds above the previous year's pruning and on the outside of the branches, and leave two or three. Cut at a slight angle with the bud eye on the high or upper side of the slant. This is called directional pruning. The strength will go to these topmost buds and growth will develop outwards, helping to keep the inside of the plant open for light and air. If however an arching or drooping shape is required, you should cut to an inside or topside bud on each branch to create more vertical branching. Cut out small intermediate branches.

Wrong! Inefficient pruners make a jagged cut which will harbour disease and virus infections. Wrong! Cut at the right angle but too high. Sap will rise only to the bud.  The rest of the stem will die back. Wrong! Cut too close to the bud and sloping towards it. Moisture will seep into the bud. Right! Correct clean cut and made about 6 mm ( in ) above an outward pointing bud and at an angle indicated by it. By cutting back to this, the new growth will develop outwards and not into the centre of the bush.  Sun and air will be able to get in.

If you wish remove all horizontal branches within 10 cm (4 in) of the ground, cutting close to the stem or trunk. If there are a number of strong upright stems, shorten them by at least a third and cut to a top or side eye or bud, never to one pointing to the ground. Remember that other dormant eyes will sprout branches below the cut. In a few weeks the new shoots will appear and this is the time to apply a dressing of organic fertiliser or manure.

Once the new growth has matured sufficiently small buds will begin to form. A spraying with endosulfan at this stage will control any insects present, particularly tip borer which attacks new hibiscus shoots.

The real old timer bush that has large, old, hard wood produces small flowers because of the equivalent `hardening of the arteries'. The plant needs rejuvenation by drastic pruning. This calls for a pruning saw. On these old plants with stems and branches 5 7 cm (2 3 in) thick, it is best to saw them off 30 - 60 cm (1 -  2 ft) from the ground on a slant. A whole new hibiscus, bushy with nice foliage and better flowers will result. It may take a little longer to recover than a younger plant but the results will be worth the wait. Several growers prune drastically this way every four to five years to maintain vigour in their plants. After pruning particularly heavily, do not over water; because of the loss of leaf, the plants do not need and cannot cope with excessive moisture. For similar reasons, neither should you apply Nitrophoska or other chemical fertilisers.

A general rule in pruning hibiscus is to cut the plants back one third all over. You can, however, leave a few old stems intact that will provide a few early blooms. Some of the older types produce their best blooms on old matured wood and these should only be pruned lightly to maintain shape. A mulch of either cow manure, spent mushroom compost, garden compost or leaf mould is recommended after pruning.

Prunings run through a mulching machine make a good base for starting a compost heap or when broken down are excellent mulch.

When to Prune

This varies a little according to climate from late winter in the warm zones to late spring in the cooler areas. Experienced growers prune prior to the new growth appearing, and this of course depends on the weather. If one prunes too early the new growth is liable to be damaged by a cold snap, and instead of good constant growth the plant tends to grow in a stop start pattern until the weather settles down. Similarly if you prune too late the plant may have already expended much of its energy reserves and the growth after pruning may not be as vigorous. As usual in gardening observation will let you know which time is best. Usually, before hibiscus shoot out, the older bottom leaves turn bright yellow and drop.

Some experienced growers have even pruned their plants in the middle of the flowering season around autumn. This means that they cut off all their flower producing wood, however, the plants shoot out immediately and have made up beautifully by winter. As the weather warms in spring the grower is then rewarded with a mass of flowers. This method of pruning can be employed when flowers of a particular variety are required most of the year around. By planting two plants of the variety needed and pruning one in spring and one in autumn a constant supply of blooms is assured. It is also handy when one is showing blooms or entering the garden in a spring garden competition.

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