Growing plants from seeds is not as hard as you might think, even though many of us have tried and failed! One of the most common mistakes people make is planting the seeds too deeply. It would be best if you only planted seeds deep in the soil as the seed is wide. When seeds are planted too deeply, the tiny plants emerge and begin to grow but do not reach the surface before they run out of stored food. Follow these instructions for growing cacti from seeds, and you will surely be successful.
It is best to use fresh seeds when growing most cacti. Seeds can be obtained from a commercial source or collected from a plant in your collection. Take care when collecting seeds from a cactus collection. Some cactus species hybridize freely, and true seed cannot be assured unless pollination has been monitored carefully.
A good potting mix, amended with ½ its volume of granite, perlite, or pumice for drainage, makes a good mix for growing cacti from seed. The soil must be as pest-free as possible. To pasteurize soil, put it in a shallow heatproof pan, place it in the oven at 300 °F (150 °C) for 30 minutes. Most commercial soils are at least pasteurized, if not sterilized. Check the label.
Be sure that all containers to be used are clean. The type of container is not important, but shallow ones are preferred. Water the soil thoroughly and let it drain completely before planting. Spread the seeds evenly over the top of the soil. Cover the seeds lightly with the mix or very fine sand. When planted, cover the container with any transparent lid. This will retain moisture and allow light to reach the seedlings.
Cactus seeds need both light and warmth to germinate. A sunny window is a good location, but be careful the light is not too strong and therefore too hot. The moisture retained by the cover should be sufficient to germinate the seeds. Most cactus seeds germinate within 3 weeks, but some take much longer, be patient. Once the spines are showing, raise the cover for ventilation during the day. Do not allow the soil to dry out. The amount of water will depend on how much light and heat the seedlings receive. Watch the seedlings carefully. Do not swamp them in puddled water but do not let them dry out completely.
Seedlings are ready to transplant into larger containers when they are the size of marbles, between 6 months to a year after germination. Be sure the soil mix is very well-drained, and the container is no larger than twice the plant's diameter. Plants can be grown in clumps or groups of 6 to 8 per pot at this size until they are about 1 inch (2.5 cm) across, then separated and individually reported. Lift the small plants carefully from the growing mix, place in the new container, firm the soil around the roots, and water in.
It is usually best to let the young plants recover from transplanting in a shaded area. Even in cacti that naturally grow with full sun, seedlings will be tender to the full sun until they are older. Acclimate a young plant to the sun gradually, beginning when it is about 1 inch (2.5 cm) across. It is often easier to acclimate young plants to the sun in the winter and provide some shade in the summer until they are about 3 inches (7.5 cm) across.
Fertilize young seedlings monthly in the growing season, usually the warm season. Use a formulation specifically for cactus or an all-purpose soluble houseplant formula at ½ the recommended strength.
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With the increasing popularity of succulent plants and cacti, some are wondering about growing cacti from seed. Anything that produces seeds can be reproduced from them, but this is not true of every seed. Cactus seed growing might move along easily without your help if conditions are right, but this is unlikely. Some seeds that drop in the natural habitat may take many years to germinate. Getting them started may be a process you’ll need to do yourself. Successful cactus seed germination results in more plants to expand your collection.
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.
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.
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.
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.
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.
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.
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.
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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Grow cacti in free-draining compost, ideally peat-free cactus compost or peat-free multi-purpose compost with added vermiculite, grit or perlite, to aid drainage. Water sparingly from March to September but avoid watering completely for the rest of the year.
In this Golden Rules video, Stan Griffin of Craig House Cacti reveals his three top tips on growing cactus plants with success, including when to water and feed, and when not to. He also gives advice on how to take cuttings from cacti:
More on growing cactus plants:
Follow our steps to growing your own cacti from seed, below.
Many plants get their common names from a defining physical characteristic, and the starfish cactus (Orbea variegata), also referred to as a carrion flower, is no exception. Although the starfish moniker refers to the plant’s pleasant, star-shaped flowers, its other nickname -- carrion flower -- refers to the rotten smell it gives off. If growing novelty but stinky cactuslike succulents appeals to you, the starfish cactus won't let you down. The starfish cactus, which grows in U.S. Department of Agriculture plant hardiness zone 9 through 11, performs best in full sunlight in a mix of well-draining, inorganic and organic sandy mediums.The starfish cactus is a low-maintenance plant that doesn’t need fertilization.
Soak the blade of a serrated garden knife in a solution of one part all-purpose household bleach to nine parts water.
Cut a 4- to 6-inch portion from the tip of a healthy stem of the donor cactus. Make the cut at a 45-degree angle using a serrated garden knife cutting the plant at a 45-degree angle prevents water from accumulating in the cut portion of the donor stem.
Pour 1 tablespoon of a rooting hormone powder containing auxin on a sheet of wax paper. Wipe the blade of the knife with a cloth moistened with isopropyl alcohol.
Square off the cut end of the cutting with the garden knife and dip the cut end of the cactus in the rooting powder. Position the cutting upright outdoors in a covered area and allow a few weeks to a couple of months for the wound to callus over. A callused wound has a drawn, grayish appearance and is completely dry.
Pinch off any leaves that grow from the bottom 2 inches of the cutting. Sieve 1/2 gallon of horticultural perlite, 1/4 gallon of coarse river sand and 1/4 gallon of sandy loam through a soil sifter with 1/2-inch apertures into a container and mix.
Place a piece of mesh screen in the bottom of an 8-inch pot and pour the propagation medium inside until it reaches the top. Tamp the propagation medium down with your hand.
Insert the cutting 1/2 to 1 inch deep in the propagation medium. Top dress the propagation medium with about 1/3 inch of fine gravel. Place the cactus in an area indoors or outside that receives full sunlight and good air flow and has a temperature of at least 65 degrees Fahrenheit.
Water the cactus with distilled water one or two days after planting. Use a watering can fitted with a fine rose to water the cactus until water drains from the pot.
Sieve 1 gallon of horticultural perlite and 3/4 gallon of sandy loam into a container after one to two months and mix. Pour the growing medium to within 2 inches of the top of a 12-inch pot with a piece of mesh screen at the bottom.
Scrape away the top dressing in the original pot and carefully scoop the starfish cactus and its root system from the pot using a garden trowel. Place it on top of the growing medium in the 12-inch pot. Spread the roots out laterally and fill the pot to the top with the remaining growing medium.
Cover the growing medium with fine gravel and irrigate the starfish cactus until water drains from the pot. Check the moisture of the growing medium every few days with your finger and water it until water drains from the pot.
Transplant the cactus to a larger pot after one year. Don’t irrigate the starfish cactus during winter.