Pruning a Lemon Tree: Water Shoots, Thorns and Rootstock Suckers

Prune after harvest, before the spring flush

The window is between picking the last fruit and the start of the new growth flush, which in most places means late winter to early spring. Cut then and the tree pushes its energy into the shoots you left. Prune in late summer and you either remove next season's flowering wood or force a soft flush that gets caught by cold.

You can pinch out a stray shoot at any time of year. What you save for the proper window is anything thicker than a pencil, and anything that changes the shape of the tree.

Never take more than about a quarter of the canopy in one year. Lemons respond to a hard cut with a mass of vertical water shoots, and you spend the next two seasons undoing it.

Water shoots: what they are and which to keep

Water shoots are the thick, vertical, fast growing stems that appear from the main branches, often three feet (90 cm) in a season, with long spaces between the leaves and big thorns. They are the tree's response to a hard cut or a heavy feed. They will not carry fruit for years, they shade out the productive wood beneath them, and they distort the shape.

Take out most of them, but not all. A water shoot in a genuine gap in the canopy is useful: shorten it by about a third in early summer and it branches, and those side branches do flower. The test is position. If it is growing into open space where you want wood, keep and shorten it. If it is growing straight up through the middle of the tree, remove it flush at the base.

1. Take suckers below the graft first Anything coming from below the swollen graft union is rootstock, not lemon. It is usually more thorny, with different leaf shape, and it grows faster than everything else. Tear or cut it off flush the moment you see it, at any time of year. Left alone it takes over and you end up with a vigorous, fruitless tree.
2. Then dead, damaged and crossing wood Cut back to live green tissue. Any branch rubbing against another will wound and let disease in, so remove the weaker of the pair.
3. Then the vertical water shoots Remove them flush with the branch they came from, leaving no stub. A stub sprouts three new water shoots in place of the one.
4. Then open the center Thin enough interior growth that you can see daylight through the canopy in places. Air movement through the middle is the single biggest thing you can do against scale and sooty mold.
5. Shorten anything overreaching last Cut back long branches to a bud or a side shoot facing outwards. Do not leave a stub beyond the bud; cut about a quarter inch (5 mm) above it on a slight angle.

Thorns and how to work around them

Lemons are properly thorny, and the thorns on vigorous young wood and on rootstock suckers can be an inch and a half (4 cm) long and hard enough to go through a thin glove. They are worst exactly where you have to reach: on water shoots in the middle of the tree.

Wear thick leather gauntlets that cover the forearm and use long handled snips rather than reaching in with your hands. Take the shoot out in two cuts, one to shorten it to a manageable stick and one flush at the base, so you are not wrestling a whole thorny branch out of the canopy.

You can shorten thorns on branches beside a path with snips without harming the tree, and thorniness reduces on its own as wood matures. Do not remove thorns wholesale from young growth in the hope of a thornless tree; you are just wounding it repeatedly.

Root pruning when the pot cannot get bigger

Once the tree is in its final pot, every second or third year in early spring take the tree out, cut about two inches (5 cm) off the outside and bottom of the rootball with a bread knife, and repot in the same container with fresh mix around the outside.

Reduce the canopy by roughly the same proportion at the same time, so the remaining roots are not asked to support more leaf than they can. Water in and keep the tree out of direct sun for two weeks. Note the date you did it; getting the interval right matters and three years is easy to lose track of.