Cacti (Cactaceae) are very popular ornamental plants. We give expert tips on what to consider when caring for cactus outdoors.
In general, the cactus family includes more than 100 genera and over 1,500 species. These numbers alone suggest that cacti are significantly more diverse in terms of their morphology and physiology than one might initially assume. There are tree-like species such as Pereskia grandifolia, but also very tiny species such as Blossfeldia liliputana. What they have in common, however, is that they are all based on the American continent. Here their occurrence extends from southern Canada to Argentina and Chile. They colonize different habitats from tropical rainforests to arid deserts. What these very different habitats have in common: Seasonal water availability.
Cacti belong to the group of succulents. They can store moisture in their tissues and survive even when it is very dry. In addition, the thorns minimize water evaporation and also protect against predators. Just as they can endure exhausting heat, hardy cacti also survive temperatures of up to an almost unbelievable -20°C. The hardy species include Chamaecereus silvestrii and Cylindropuntia imbricata.
Not least because of these properties, cacti are considered the Spartans among the ornamental plants. Put them in the sun, give some water and nothing more needs to be done. But there are also a few points to consider when caring for cactus outdoors. The requirements vary between the species, but some tips and tricks for location, watering, fertilizing, and repotting must be observed so that the small green cactus in the garden can also become a really big one.
1. The right location
Most cacti are used to full sun and a lot of heat. If you give them a spot in full sun, they will grow best. So preferably place your cactus in an area with as much direct sunlight as possible, for a beautiful, healthy cactus. As a guideline, you can maintain that your cactus gets direct sunlight for at least 5 hours a day.
If you place your cactus too dark, it will take a while for your plant to indicate this. That beautiful barrel cactus will gradually grow into a tip and an Opuntia or disk cactus will make long, thin shoots instead of new discs. In short, the new growth really looks different. The cactus tries to grow upwards quickly in order to get closer to the light. This is called stretching or etiolating.
If you have a cactus that shows this etiolation, it is important to find a brighter spot for it. You can cut stretched discs, so that the plant will grow beautiful discs again. Unfortunately, you cannot get a barrel cactus back into shape. Eventually it will thicken again, giving you an interesting hourglass model.
Full sun can sometimes even be too intense for cacti. This especially happens in the middle of summer, when the sun burns on your cactus for hours. Then a cactus can get burn damage, which looks like a discoloration. The beautiful green of your cactus will then turn yellow and in very extreme cases even white. Get your cactus out of full sun if you see this.
If your cactus only has a yellow discoloration, it will often turn green again on its own. If there is a large white spot on your cactus, it will remain visible. So be careful when you buy a new cactus or when it is very sunny, in the middle of summer. It may be that the full sun is just a bit too intense.
2. Watering properly
Cacti need regular irrigation, especially during the growth and flowering period in spring and summer. However, it should not be watered too often and waterlogging should be avoided, as otherwise there is an increased risk of rot. The substrate should (almost) completely dry out before watering again.
When caring for cactus outdoors, it is advisable to ensure sufficient water supply, especially in the spring months. You should water fairly regularly in summer. However, do so only on sunny days or after longer periods of dryness in order to avoid overwatering due to subsequent rain.
At the change of season, the watering frequency should be gradually reduced. Particular attention should be paid to watering in winter. On the one hand, there is an increased risk of the soil becoming wet and fungal infections spreading. Additional rain protection should therefore be installed. On the other hand, a dry period in the winter months encourages many cactus species to flower in the following year. However, this can only be implemented with potted plants that overwinter under cover.
3. The right fertilizer
It is a common misconception that cacti don't need fertilization. On the contrary, there are few plants that are as dependent on fertilization as cacti. Deficiency symptoms often appear late and can then no longer be remedied quickly. Fertilizing in good time is therefore essential in order to be able to enjoy the plants for a long time.
Outside, coarse cattle horn shavings can be added to the ground in the garden or to the substrate in the pot as a basic fertilization. Nevertheless, you should also fertilize from March. In the months of April to June a 14-day fertilization has proven itself. You can give between 20 and 30 grams of a complete fertilizer (e.g. blue grain) per square meter.
The liquid fertilizers available on the market (usually: 1% nutrient solution) should be used regularly. In July it is advisable to only lightly fertilize the plants. It is also an advantage to add a potassium fertilizer (potassium magnesia 20g/m2) at the end of August. As a result, the plants harden well and are well prepared for the coming winter.
4. Repotting and transplanting
If you grow your outdoor cacti in pots, you need to consider repotting them.
Fortunately, cacti don't need to be repotted that often. That is often a challenging job because of all the spines. Cacti like to be a bit tight in their pot and can stay in the same pot for quite a few years.
Do you notice that your cactus hasn't grown all summer, or that roots are growing out of the drainage holes? Then it is time for a bigger pot. Choose a pot that is a size larger and has holes in the bottom. Terracotta pots are ideal for cacti, because the soil in them dries up faster.
When repotting, use special cactus soil or mix sand and stones through your potting soil, so that the soil allows more water to pass through. If necessary, wrap your cactus in newspaper and put on sturdy gloves (we recommend a few here) to repot your plant. We recommend repotting your cactus in the spring.
If you have a large cactus in your garden that needs to be transplanted, read our article on “How to transplant a large cactus“.
5. Caring for cactus outdoors in winter
Whether and how you have to hibernate and care for your cactus during this time depends on the species. Some cactus species need a cool break, which does not necessarily have to take place in winter in order to set flowers, for example the Christmas cactus (rest in August) and all Mammillaria and Rebutia species (rest between October and February at 5 to 15°C).
However, many other cacti overwinter warm and bright, which means they can stay in their location all year round. Please note, however, that the lower light yield means that the growth of the plants is restricted in winter and that they therefore need significantly less or no water and no fertilizer.
You may also be interested in the next article “Can cactus survive winter?“.
Summary: Caring for cactus outdoors
1. Choose a bright, but not full sun, location – unless the species requires it.
2. Water deeply, but not too often.
3. Fertilize cacti with cactus fertilizer during the growing season.
4. Repot your cactus regularly, because the substrate will eventually be depleted or the space for the roots used up.
5. Some cacti should move to a cooler place in winter in order to be able to keep their natural resting phase.