Growing Gasteria

Gasteria do not pose too great difficulty in growing. The Cfb climate of Belgium however (Temperate, no dry season, warm summer) means you have to grow them in a greenhouse or inside the house.

The Gasteria collection of Belgium's National Botanical garden, Meise

Part of the Gasteria collection in the National Botanic Garden in Meise, Belgium.

Propagation

Propagation

leaf cuttings

Gasterias have developed a passive defence method in that a broken leaf fallen on the ground will root and small plantlets will grow from that point.

This is used to propagate plants: a fully grown leaf is carefully detached from the base and left to dry for a couple of weeks in shade. Then the base of the leaf is placed on well draining soil and left. After some time (6 months?) the leaf may have rooted. Plantlets can be detached from the rooted leaf when big enough to handle. This means you have propagated an exact clone of the motherplant.

seeds

Gasteria flowers can be easily polinated with a small brush. When a flower is fertilized the developing fruit will switch from a hanging to an upright position. This is a sure sign fertilisation has worked.

The fruit is then left to develop further and by winter it will dry and split open. Fruit will be dispersed by the shaking of the fruit and fall to the ground. To avoid this you can wrap the flowerstalk in some netting or old stocking. Or you can carefully cut the fruits when you see the first signs of splitting and let them dry further indoors.

Seeds are small and black. They should be left one or two months before sowing. After a year they lose their fertility quickly, so don't wait too long before sowing.

G. polita leaf offset. Photo Cok Grootscholten

Young Gasteria

Often young Gasteria - juveniles - look very different to the adult form.
One difference is the shape of the leaves, another is the presence/absence of tubercles.

While adult plants form a rozette, their young form can be distichous. This is caused by the cross section shape of the leaf: when this shape is approx. oval in the juvenile plant, its form is distichous. But as soon as a keel develops and the cross section shape becomes triangular, the plant starts to develop a rozette. A rozette shape is a simple consequence of the cross section of the leaves: impossible to stack triangular leaves in a distichous form.

In some species this difference is so outspoken that with a juvenile alone, it is impossible to recognize the species. Some notorious examples are G. acinacifolia and G. nitida. On the other hand this can also become a determination factor: when the juveniles look different to the adult, one can put a finger on the species. These differences can last for many years depending on the growth conditions.

Other species that show clear dimorphism are G. pulchra and G. visseri.

Juvenile G. acinacifolia

young G. acinacifolia are distichous and the leaf surfaces are covered in tubercles

Adult G. acinacifolia

adult G. acinacifolia form a rozette and the leaf surfaces are smooth and deeply channelled

Juvenile G. nitida

juvenile G. nitida look very much like G. armstrongii with tubercled, distichous leaves

Adult G. nitida

Adult G. nitida form a rozette of smooth, shiny triangular leaves

Growth conditions

Light

Gasterias require a lot of indirect sunlight: a bright but shaded position with some dappled sun is ideal.

One must be particularly careful at the end of winter when day length and bright sunshine return in March and early April. that's when they get burned! I pull a shade cloth over half of my greenhouse from March to end August, then remove it for winter. Keep an eye on your plants so they don't get sunburn.

Do not confuse light with temperature! bright light should not coincide with heat in the case of Gasteria. Make sure they have fresh air: open the door and use a fan.

In summer I keep bigger plants under my shaded terrace in the open. In the evening they receive some direct sunlight for about half an hour and because they are used to it they colour nicely. They like it. Species who can take some full sun are acinacifolia, croucheri, excelsa, bicolor, nitida.

Also in summer I keep G. rawlinsonii (in hanging baskets) outside in rain and wind, hanging under a tree. This mimics their natural conditions in the deep kloofs of the Baviaanskloof. They love it!

Soil

Gasterias require a very aerated and draining soil medium that dreis out quickly but retains a minimum of moisture.

My mixture consists of 2/3 inorganic grit (pumice, stones, redstone, shale), 1/4 loam, and a bit of organic matter. I use the loam because it holds some moisture even in very dry conditions and it binds the rest together.

Bims

Bims is the German name for the graded product made from pumice . Thick layers of grainy pumice were ejected by volcanoes in the volcanic Eifel field, an area between the river Rhein and the Belgian border. This region has been volcanicely active for 45 million years with major eruptions still taken place as recent as 700 000 years ago. Even today there is some volcanic activity.

These grainy pumice layers are excavated, sorted and used for different purposes like road construction, but also as a growing medium for plants. The German bims is light and porous, it contains air and can absorb some water. It's getting really popular amongst succulent growers in western europe. It has several advantages:

it gives a very airy medium which encourages root growth.
it dries out quickly after watering and even when wet it contains a lot of air
it is pure mineral and erodes slowly to a sandy soil
no insect diseases on the roots (root mealies) at all in this medium: the sharp pumice kills the insects

Growers use it for cactusses, Haworthia, and Gasteria. Some use it 100% pure, others mix it with other components. If used pure, one should consider that

you need to water more frequently
you must add fertilizer to your water because pumice does not contain any nutrients

Cactus-, succulent enthousiasts and commercial growers prefer it mainly because they lose fewer plants to root problems.

Some Gasteria species who really thrive in pure bims are:

G. pillansiii (recommended for this species)
G. baylissiana
G; glomerata
G. glauca

Other species also grow well in it, but I find that a mix with cactus soil and some organic matter makes up for the nutrient deficiency.

Shale

In South Africa I have noticed that many growers use pure Shale (mudstone) as a medium. They do so for the same reason: fewer root problems and diseases, yet an airy soil. Shale is a metamorphosised sedimentary rock and weathers back into clay. This means that it contains more nutrients than pumice.

I have tried it recently with some species I keep outside in summer: they seem to do well.

80m thick tephra layers near the Laacher See in the Eifel

Gasteria in pure bims

G. carinata in pure shale at Babylonstoren, SA

Water

During the growing season I water on average once every three weeks. In very hot weather an occasional spray with the garden hose may be given in the evening. During winter (november - march) I do not water at all, although in february I may give some water to Gasterias in hanging pots and some particularly parched small plants. Plants that are kept inside, (in a warm living room) will receive some water every month because they tend to keep on growing.

Air

Like any succulents, Gasteria enjoy fresh air. So as soon as temps outside are above 20C open windows and doors if your greenhouse.

G. rawlinsonii in hanging baskets are hung outside in/under a tree when temps reach 25C. I keep them there all summer.
However if one of our notorious rainy summers occur, with rain every day for a week or more, I put them back inside the greenhouse to dry out.

As said before, if you have a shaded but bright spot outside your house (terrace, window sill) where you can control the amount of rain they get, go for it, they like it!

Temperature

I speak from a viewpoint of growing them in a temparate European climate.

Gasterias grow best in day temps between 20-35C and night temperatures of 10-25°C. They need cool nights. They start to grow in spring as soon as day time maxima go above 15C. They also need a resting period with cooler temps (a winter) in order to produce flowers in spring.

Above 35C they will shut down and will stop growing. That's why putting them outside in summer is a good idea.

Problems

Pests and diseases

Gasteria in a cool western European climate do not have many diseases. Root mealies is the major problem.

root mealies make snow white deposits

Root mealies

Root mealie bugs (Rhizoecus sp) are below ground mealy bugs: insects that feed on the roots of plants. There are many species and they feed on almost any plant, but they are fond of succulents (inc Cacti).

You recognize them by the snow white deposits they make on the soil or the inside of the pot. If you unpot a plant, look for white patches on the pot and the root clump. If you see them, check the roots, you will find the bugs: they are only a couple of millemeters long and white or pink. If left unchecked they can kill a plant.

How to avoid them?

always check the roots of any new plant you acquire. Rince the roots and repot
make sure you do not cross contaminate old soil with new one
thoroughly clean any pots or saucers with water and soap before reusing them
use a pure mineral soil like pumice (bims), never any insects there

What to do if you find them?

a really badly infested plant: throw it away pot and plant
cut of all roots and wash the plant. use a fresh pot and root it again
treat the plant with a systemic insectide : soak the pot in an insecticide solution
remove any soil and wash the roots under water. Wash them carefully and remove any mealies. This would still need treatment with an insectide solution: soak the roots a couple of hours in it.

black spot on a leaf

Black spot

Black spot is a fungus infection which is not lethal to the plant. It forms an ugly spot (or more than one).
It cannot be treated or removed once it is there. You will have to wait until the leaf dies and you can remove it. Old leaves are more prone to black spot. And some species are more susceptive to it than others: G. bicolor, G. brachyphylla for instance.
The cause is the combination of moist and cold conditions. With a high humidity and cold temps in your greenhouse during winter they will occur.

To avoid black spot you can spray a fungicide preventively just before winter. Or keep your plant indoors.
In dry climates it is seldom seen.

Snails, caterpillars and mice

If you bring outdoor plants into the greenhouse for winter, you will import some unwanted visitors as well.

Snails and caterpillars like a bit of succulent plant for dinner. Use snail bait to kill the snails and be on the lookout for caterpillars or use an instecide. In particular be vigilant in spring when they wake up.

Every so often a mouse may take a bite out of a juicy succulent. Spines will not stop it. If it comes in for a daily lunch, use a mouse trap.

What not to do

I make mistakes, probably more than you, and I have paid for my sins. Let me tell you about them, so you can avoid them.

Pots too big

If you repot be sure the rootsystem is capable of sucking the new volume of soil dry. If you start trimming roots and offshoots, the same size of pot may be the right one.

A plant which bursts out of its pot, I only give one size larger, not more. This rule counts especially for small plants: do not overpot.
Exception: for very sturdy and healthy plants, like a G. excelsa, you can use +2 sizes. If possible, consider planting them in full ground in your greenhouse, they'll love it.

Over fertilize

Do not use any more fertilizer than necessary. If you do plants will suffer: burning of the leaves, dying back of leaftips.

I now use Peters Professional Fertilizer 1e Fase: 10+52+10+sporen, 7ml/10l water.

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