Bald cypress bonsai

Placement

Bald cypress wants full sun and warmth throughout the growing season: that is what gives it vigorous shoots and dense foliage. Grow it outdoors. It enjoys hot summers, but in very hot, dry regions, light shade protects its needles: between 81 °F and 90 °F, filter out 20 to 30 percent of the light; above 90 °F, it only tolerates the heat if the air is very humid.

In mild climates, it can stay outdoors all year. Elsewhere, keep in mind that in a pot it barely tolerates frost, unlike trees in the ground: it is comfortable above 25 °F. During cold winters, shelter it to protect its roots from very low temperatures.

Pests rarely attack it. The sneakiest ones live in the root ball: root aphids and root mealybugs, which feed on the reserves the tree stores there. If growth slows for no visible reason, repot, get rid of as many of these insects as you can, then apply predatory nematodes to the roots on a regular basis.

Soil mix

The mix needs to hold water, since the tree is a heavy drinker, while staying airy, because in a pot its roots need oxygen. A conifer mix of equal parts akadama, pumice and lava rock makes a good base. Sift the akadama and lava rock to remove the dust, which clogs the pot. If you cannot check on the tree often, increase the share of akadama or add a little potting soil for better water retention; in a very rainy climate, add more lava rock or gravel instead. Replace the mix when you repot, since it compacts over time.

Watering

In the wild, bald cypress grows with its roots standing in water and forms “knees,” woody growths from the roots that rise above the water. In a pot, the rule is different: the root ball should never dry out completely, but it should not stay soggy or sit submerged either, or the roots will suffocate.

In summer, its needs are high: check the pot every day and water as soon as the surface dries, until water runs out of the bottom. If you cannot water often enough, setting the pot in a shallow tray of water works as a backup, as long as the root ball can still breathe. Wet the roots and the soil, not the foliage or the trunk. In winter, without leaves, it drinks much less, but the root ball should stay slightly moist.

Fertilizer: feed generously as soon as the leaves appear to get long shoots that will become branches, using a liquid fertilizer every one to two weeks or a solid organic fertilizer. Stop feeding during the hottest part of summer, resume moderately in fall, then stop once the foliage changes color.

Pruning

Bald cypress produces lots of buds on the trunk, the branches and the forks. Remove early any that do not serve the design.

• Spring pruning: when the buds swell, cut to the length you want along the woody structure; the tree buds at the cut and further back.
• Early summer pruning: let the new shoots grow until they form side branches, then shorten them. Cutting too early often leads to dieback in fall. At the same time, remove unwanted shoots, such as those on the underside of branches, along with about half of the needle mass.
• Branches: cut them in fall or early spring.

Styles: bald cypress can be trained as a formal upright, with its branches lowered by wiring, or in the flat-top style developed in North America. In this style, the branches are allowed to rise and the crown to flatten like that of old wild trees, above a tapering trunk that flares well at the base. Trees collected from Louisiana swamps have become major collection pieces.

Wiring

Wire only in spring, when the buds swell: at other times, wiring can damage the tree. Young branches and twigs are easy to shape; older wood turns stiff and brittle, so set the branch structure while the branches are still young.

Choose wire about a third as thick as the branch, wrapped at about 45°. Check it often during the growing season: the wire can mark the bark within one to four months. Remove it by cutting it at each turn rather than unwinding it. To lower thick branches, use guy wires or twine anchored to a sturdy root or to the pot instead.

Repotting

Repot in spring, when the buds swell. The roots grow fast, thicken quickly and stay soft enough to prune easily. A young tree is repotted about every two years, with root pruning, and right away if the roots circle the pot or the root ball starts lifting. An older tree can wait three to five years. As with any conifer, never bare the roots completely: keep part of the root ball intact. Both deep and shallow pots work. After repotting, keep the tree out of the wind and full sun until it recovers.

Propagation: seeds and cuttings succeed fairly easily. Air layering remains the most widely used method: use rooting hormone, since the tree readily forms callus and roots, and remove a fairly wide ring of bark, because it easily closes a narrow cut.