Gadenin日本語Get the appWhy the leaves change, and what pruning does about it
Eucalyptus carries two completely different kinds of leaf. Juvenile foliage is round or oval, stalkless, often clasping the stem in opposite pairs, and coated in a blue-silver bloom. Adult foliage is long, narrow, leathery, alternately arranged, hangs downward and is a dull green. Almost everyone who plants eucalyptus is planting it for the first kind and inherits the second by doing nothing.
The switch is a function of the shoot's maturity, not the calendar, and it usually starts in the second or third season. A shoot that has gone adult stays adult. What reverses it is cutting into older wood and forcing the plant to push entirely new shoots from dormant buds at the base, because those new shoots start again as juveniles.
So pruning here is not tidying. It is the mechanism by which you get the plant you wanted. Cut hard on a one to two year cycle and you have a silver-leaved shrub indefinitely. Trim lightly around the edges and you get an adult-foliaged tree with a bad haircut.
Coppicing: the hard cut
Coppicing means cutting every stem down to a short permanent stump, called a stool, and letting the plant regrow from the base. Eucalyptus takes this extremely well because it carries dormant buds under the bark and, in many cases, a woody swelling at the base that exists precisely to regenerate after fire. The regrowth is fast: several feet of new stem in a single season is normal.
Wait until the plant has completed at least one full growing season in the ground and has a stem thicker than a pencil at the base before the first hard cut. Cutting a plant that is still establishing can kill it, because it has not yet built the root reserves the regrowth is paid for out of.
Cut when the coldest weather is over and before growth accelerates, so the stumps are not sitting open through hard frost and the plant can respond quickly. Cutting in the middle of a hot dry summer is the other thing to avoid; the plant will regrow, but it does it under stress and the shoots are weak.
- Choose the stool height Cut every stem back to between four and twelve inches (10-30 cm) above the ground. Lower gives a mass of stems from the base; a little higher gives a slightly more upright plant. Keep the same height at every cut so the stool stays compact rather than creeping upward year by year.
- Cut cleanly with the right tool Use loppers or a pruning saw, not shears. Make each cut at a slight angle so water runs off, and leave the surface smooth. Ragged crushed cuts are where rot gets in on a stump that has to survive until the buds break.
- Leave the stump alone afterwards Do not seal the cut, do not paint it and do not pile mulch over it. Sealing traps moisture against the wood. Bare, dry stump surfaces callus over on their own within a season.
- Water once, then wait Give the stool one deep soak of about five gallons (20 liters) after cutting if the ground is dry, then leave it. New shoots normally appear within three to six weeks in warm weather. Nothing appearing after eight weeks in active growing conditions means the cut was too severe for that plant's reserves.
- Thin the regrowth once A stool can push twenty shoots. When they are a foot (30 cm) tall, rub or cut out the weakest so five to eight strong stems remain evenly spaced. This gets you usable stems instead of a thicket, and it lets air through the middle.
Choosing a cutting rhythm
How often you cut depends on what you want from the plant. Annual cutting gives the most reliably juvenile foliage and the smallest plant; a two-year cycle gives longer, more usable stems and slightly more variation in leaf shape by the end of the second season. Beyond two years the adult foliage takes over and the stems get too thick to cut with loppers.
Pick a rhythm and stay on it. The single most common failure is skipping a year, then skipping another, and finding that the plant is now a fifteen-foot tree with a trunk that needs a saw and a decision about whether it should exist at all.
| Approach | Cut frequency | What you get | Main risk |
|---|---|---|---|
| Low stool | Every year | Dense silver juvenile foliage, plant under 6 ft (1.8 m) | Needs the cut done without fail |
| Tall stool | Every 2 years | Longer cutting stems, mostly juvenile leaves | Some adult foliage late in year two |
| Short framework | Every 2 years to the same knuckles | Shrub shape with a visible structure | Framework thickens and creeps upward |
| Left as a tree | Formative cuts only, when young | Adult foliage, tree size, fast | Shallow root plate; windthrow risk |
| Neglected then cut | Once, into old wood | Regrowth is unpredictable | Plant may not resprout at all |
Never take a plant that has grown into a tree and simply top it. Removing the crown of a tall eucalyptus leaves a bare trunk that either fails to resprout or produces weakly attached shoots high up, which is worse than the original problem. Cut low or do not cut.
Formative pruning if you want a tree
If the plan is a tree, the work is done early and then stops. In the first two or three seasons, select one leading stem and remove competing leaders at the base so the plant does not build a weak fork. Take off the lowest side branches gradually, never removing more than a quarter of the canopy in one season, so the trunk clears to the height you want.
After that, restrict yourself to removing dead, broken, rubbing or crossing branches. Eucalyptus does not need or want routine canopy pruning, and large cuts on a mature trunk heal slowly. Be honest at this stage about the size the plant will reach and the fact that its roots spread wide and shallow rather than anchoring deep, which is why fast eucalyptus in wet windy ground has a reputation for going over.
Cuts to avoid
Do not shear the outside of the plant to keep it small. Clipping the tips leaves adult foliage in place, produces a dense unattractive shell of twiggy growth and forces the plant to regrow at exactly the height you did not want. Do not cut a plant that went through winter damage until you can see where live growth is breaking, because the dieback often stops higher than the brown tips suggest.
Do not make a hard cut in the last weeks before hard frost. New shoots emerging into cold weather are soft and get killed, and the plant has spent reserves for nothing. If you missed the window, wait for the following season rather than cutting late.
Keep a cutting log
Record the date of each hard cut, the height you cut to, how many weeks the new shoots took to appear and how tall the regrowth was by the end of that season. Three years of that log tells you exactly what your plant does on your ground and removes all the guesswork from the timing decision.
It also protects you from the slow drift where each year's cut is made an inch or two higher than the last. Written stool heights keep the plant compact over a decade instead of leaving you with a knuckled stump at waist height.