Bamboos: care and pruning

Watering bamboo

Bamboo is a very water-hungry young plant. It is not uncommon for a bamboo to die of thirst in summer, especially when planted near a tree. They show signs of dehydration by curling their leaves inwards.

To establish well and grow, the rootstocks of young bamboos require ample and regular watering (15 to 20 litres of water every 15 days or so) during the first year after planting. In southern regions, it is often necessary to water more frequently and mist the foliage in the evening during heatwaves.

In the following years, the plants will be robust enough to withstand occasional summer droughts.

Bamboos in pots

Potted bamboos dry out more quickly and require increased monitoring of water needs throughout the year.

To water a bamboo in a pot properly:

• in summer, ensure that the soil does not dry out between waterings. A potted bamboo can consume up to 5 litres of water per week.
• in winter, when it freezes hard, the bamboo cannot draw water, thus cannot sustain its foliage, and eventually, it dries out and dies. Water even in winter, but only when it is not freezing and sparingly. Protect them from the cold with a winter fleece or organic mulch.

Grown in a container or pot, bamboos require special attention regarding watering

Bamboo mulching

Mulching is essential, especially in the first few years to protect young rootstocks from the cold in open ground and for bamboos grown in pots. Mulching also helps to retain moisture in summer and provides effective protection against frost in winter. A good layer of pine bark often does the trick.

Afterwards, leave the dry leaves that have fallen to the ground in place, as they will form a natural mulch at the base of the bamboos.

Bamboo pruning

Whether they are non-running like Fargesia or running like Phyllostachys or Semiarundinaria, all bamboos tolerate pruning very well. Bamboo has a particularity: when its culm is cut, it does not regrow. Pruning of bamboos is not obligatory and varies according to the species and the intended use.

Why pruning?

Pruning of bamboos can nevertheless be useful. It is carried out to lighten the vegetation, allow light to enter the centre of the clumps by removing lateral branches to a certain height, and provide transparency, thus enhancing their graphic aspect.

Moreover, maintenance pruning on dwarf varieties ensures the rejuvenation of the foliage and encourages their branching. It is also a good way to contain their height and give them a shape; some bamboos can even be pruned into topiary.

When to prune bamboo?

The best time to prune bamboos varies according to the species and is done either at the end of winter or at the end of spring.

• In February-March, before the resumption of growth for cleaning up dry and damaged culms during winter.
• At the end of spring, around June-July for equalising, shaping, and thinning pruning.

An appropriate pruning depending on the use

• The bamboo hedge: Composed of tall, fast-growing species (mainly Phyllostachys), the bamboo hedge serves to obscure and provide an effective windbreak. Pruning a bamboo hedge is done in two stages: first in spring, around April-May, to cut back the old stems, and a second time in early summer, around June-July, to cut the new shoots and stop their growth. Perform the pruning either with a shear or a hedge trimmer as you would with a traditional hedge.

• Dwarf bamboos and low hedges: Used to define a border or cover a bank, dwarf bamboos offer a dense foliage and must be pruned at least once a year to remain compact and dense. Pruning of dwarf bamboos is done in the spring, around May-June, and involves cutting and equalising the bamboos to the desired height. Pruning is done with a hedge trimmer or using a brush cutter equipped with a disc.

• Giant and ornamental bamboos: Planted alone or in groups, these bamboos need to be cleaned of their old culms and highlighted through appropriate pruning. First, remove all the old, faded, twisted, or broken culms using a saw or a pruning shear at the end of winter, around March-April. Then, at the end of spring or early summer, proceed with thinning pruning to highlight the culms:
• On the new shoots, remove either by hand or with a pruning shear, the young lateral branches in formation up to at least 1 metre in height to expose the culm.
• Then, using a fine-toothed saw, cut a few old culms at the base (no more than 10 to 20%) to thin the clump and allow light in. Only cut culms that are at least 2 years old. Do not discard these old culms; they will serve as stakes once dry.

The transparency pruning reveals the graphic design of these bamboos

Fertilising bamboo

The supply of nutrients for bamboo is important, especially for giant bamboos and those in pots. Bamboos thrive in rich, fertile soil. Therefore, it is essential to maintain the richness of the soil. A fertiliser helps bamboos grow better and reach their full potential.

• In open ground: at the beginning of spring (in February), you can add compost or a maintenance fertilisation.
• For bamboos grown in pots: a special bamboo fertiliser, rich in nitrogen will be more suitable. Renew this fertilisation in September.

Bamboo care

Bamboos are resistant to most diseases and pests. They can sometimes be more vulnerable, especially in winter when it snows or in summer when they are planted in pots on a terrace or under a veranda.

• When the weather is warm and humid, mealybugs can infest the foliage of bamboos and leave behind white, farinose or cottony masses. The affected leaves eventually turn yellow and fall off, sometimes leading to the death of the plant. Spraying a mixture of vegetable oil (rapeseed or olive oil), 90° alcohol, and black soap can suffocate them.
• Sometimes red spiders can also cause yellowing and drying of the leaves, which eventually fall off: a simple acaricide will deal with these unwanted pests.
• When it snows, clear the culms of snow accumulations to prevent them from breaking under their weight.
• If temperatures drop for an extended period below -15°C, -20°C, it is advisable to store less hardy species grown in pots in a warm place inside the veranda.

Save your bamboo

Why isn’t my bamboo growing?

With their rapid growth and sometimes invasive character, it’s surprising to see bamboo stagnating. Several explanations are possible:

Case No. 1: Growth varies depending on soil quality as well as species; bamboo takes time to grow. Most bamboos reach their maximum height after 4 or 5 years, and sometimes even 10 years for giant species.

Case No. 2: The soil is not fertile enough. While bamboos thrive in any good garden soil, the quality and moisture content of the soil determine their proper development and growth rate. They all appreciate moisture in summer, warmth, and fertile soils, and they grow quickly when these conditions are met. They will quickly colonise any acidic or neutral soil as long as it is rich, light, and cool, without excess lime. Add manure or compost at the end of winter and in summer.

My bamboo’s leaves are turning yellow, help!

Leaf drop in bamboo is normal: although the foliage is evergreen, it renews itself every spring. The leaves turn yellow, fall, and are immediately replaced by fresh green foliage. In pots, the risk of yellowing leaves is even greater. However, outside of this vegetative recovery period, the “yellow leaves” symptom may indicate that your bamboo is unwell.

• It has been stressed: If leaf drop follows planting, don’t panic. Mulch and water generously and regularly throughout the year following planting, and the bamboo should quickly regain its composure.
• It has too much lime: If the leaves tend to yellow, this may indicate an excess of lime in the soil. Add heather soil on the surface to acidify the soil, as bamboos are somewhat acidophilous.
• It is thirsty: bamboos have significant water needs (20 litres per week in the ground, 5 for potted bamboos), especially during prolonged dry spells. A lack of water will cause the leaves to dry out like straw. Water potted plants throughout the year, even in winter (except during frost), as soon as the substrate is dry. But don’t drown your bamboos: excess water would cause the same symptoms. Avoid standing water.
• It is cold: winter cold has burned its leaves. If your bamboo is exposed to cold winds, its leaves may have suffered; in spring, prune the damaged branches.
• It is hungry: the soil is not fertile enough for this greedy plant! Feed it with manure or compost. For potted bamboo, apply a lawn fertiliser twice a year (as bamboo is a grass, this type of fertiliser will suit it).