The cacti are a major family of succulents and come in a wide range of sizes, shapes and flower types. However, all of them have a few features in common. Almost all of them are leafless and have woolly or bristly cushions (areoles) on the stems. Spines, hairs or hooks can grow from these cushions.
Cacti need heat to thrive, so it is beneficial to grow cacti in a greenhouse. Many growers even devote a whole greenhouse to a collection of cacti. You might be wondering why. Well, mainly because cacti come in strange shapes and colorful flowers.
Moreover, cacti are very practical to grow. They don’t demand a lot of attention. For example, you don’t need to create a moist environment and cacti require little or no water at all from November to March. If you need to go away for a few days quite often, that is not a problem for cacti.
So, can you grow cacti in an unheated greenhouse?
It depends on how low the temperatures are where you live and what types of cacti you are growing, but generally, yes, you can grow cacti in an unheated greenhouse all year round. Even though many species need frost-free conditions, some can tolerate occasional frosts.
How To Grow Cacti In A Greenhouse?
This guide is applicable for desert cacti, which include nearly all the species in the family. However, epiphytic cacti, which means that they grow on trees, also known as forest, jungle or orchid cacti, require different care. For example, Epiphyllum, Zygocactus and Rhipsalidopsis. Their natural home is in the forests of tropical America.
1. Light – use polycarbonate glazing to allow maximum sunlight.
Desert cacti want a lot of light. The light can be not bright enough for them in a greenhouse. Regular glass filters out UV rays and very often gets dirty. The plastic cover can quickly become dull. However, corrugated polycarbonate glazing has up to 90% light transmission, so it is the best glazing for a greenhouse to grow cacti.
2. Temperature – above freezing in winter and a maximum of 70°F in summer.
How cold is too cold for cactus depends on its species. Most cacti need frost-free conditions – above 32°F (0°C). However, some of the cactus species from Chihuahuan Desert can tolerate temperatures as cold as -5°F (-20°C) in winter.
It includes the plants from the Mexican part of the region. In summer, when the temperature reaches 70°F you need to ventilate a greenhouse. Don’t forget to use shade cloth on scorching July afternoons. Bright sunlight can quickly cause yellowing or sunburn within one afternoon.
3. Watering – no water in winter and each time compost dries out in summer.
For desert cacti little or no watering is required between November and March. For proper development and regular flowering you need to water cacti thoroughly in summer. Water cactus each time the compost start to dry.
4. Growing Medium – 1/3 sand and 2/3 multipurpose compost.
Cacti need sandy compost to grow in a greenhouse. Generally, a growing medium of one part grit and two parts multipurpose compost does well. It is going to drain well.
5. Humidity – cacti thrive in dry air.
Cacti don’t like moist environment. So you need to watch out for humidity and keep it down in a greenhouse. To do so, you need to ventilate with a cool fan.
Best Types of Cacti That Do Well In A Greenhouse:
The most common species – Aporocactus flagelliformis also known as rat-tail cactus – is the easiest cactus to grow and bring into flower. It is a plant for pedestal plant stand or hanging basket.
That is because 1.5 inches wide cylindrical stems hang down and grow several inches each year. You can expect flowers to appear in spring. They are 3 inches long tubular flowers that open during the day and close at night.
Cephalocereus senilis or Old Man cactus produces a 50 ft high columnar stem in the wild but reaches only 1-1.5 ft in a greenhouse. Old Man cactus has about 30 shallow ribs and thin spines and cover of long silvery hairs. However, the pink flowers rarely appear on Old Man cactus in a greenhouse.
Cereus is a genus of cacti that are ribbed and columnar and consists of around 33 species. A favorite of many gardeners to grow in a greenhouse is Cereus peruvianus . The stem reaches 2-3 ft and ribs bear brown spines. 6 inches long funnel-shaped flowers appear on mature plants in summer. This cactus is blooming at night with slightly fragrant flowers.
It is also known as Barrel Cactus. It is in a shape of round ribbed ball with sharp spines. Barrel Cactus is a slow-growing type of cactus. For example, Echinocactus grusonii or a Golden Barrel Cactus has yellow spines and will take 15 years to reach the flowering stage.
This species come in different shapes like globular or columnar. Echinopsis is also known as Sea Urchin Cactus or Hedgehog cactus . This species have prominent ribs and sharp spines. However, their flowers are truly beautiful.
E. eyriesii blooms with white scented flowers while E. aurea produces yellow flowers. Sea Urchin Cactus is a hardy plant so you can grow it in unheated greenhouse.
It is known as a beginner cactus because it’s easy to care for, stays compacts and produces flowers. The colors of the blossom vary from white, red, pink, yellow and orange. These cacti are flowering from late spring to early fall. Each bloom lasts for only a day.
Also known as Pin Cushion Cactus. It is a large genus containing several species. Some of them are easy to care for while other are quite challenging. The most common pattern is a globe with spine-topped tubercles instead of the ribs.
The flowers can often produce fruits and grow in a ring near the top of the ball. The most recognized species is M. bocasana with silky hair, hooked spines and white flowers.
Opuntia or Prickly Pear is an indoor plant and comes in a shape of flattened pads bearing yellow flowers along the edges. The flowers can also produce edible fruits. The most popular species is O. microdasys or Bunny Ears which grows 1 ft high with golden bristles and yellow flowers.
Also known as Old Man of the Andes, these cacti have oval columnar stem which reaches 3 ft in time and branches derive from the base. Their yellow spines turn red with age and they are covered with long white hair, hence, they are called Old Man. In summer cacti bloom with red flowers.
Parodia or Tom Thumb Cacti are small, globular and flower from an early age. They also have colorful spines. P. sanguiniflora blooms with red flowers and P. aureispina has yellow flowering.
Also known as Crown Cactus is easy to grow and starts flowering from one year of age. The ball shaped stems are covered with tubercles. The flowers are long-tubed and funnel-like which grow near the base. Flowers vary from orange or pink colors and cacti bloom in early summer.
Hope that you found this blog post useful! Let me know what cacti do you grow in a greenhouse in the comments section down below.
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Happy Greenhousing 🙂