Pilosocereus pachycladus - Clever Cactus of the Month

Pilosocereus pachycladus – Clever Cactus of the Month

This month’s Clever Cactus is a tree-like azure wonder! The Pilosocereus pachycladus, aka the Blue Columnar Cactus, can grow up to 30 ft tall. Read on to learn more about this blue beauty.

A Blue Columnar Cacti Forest

  • Name(s): Blue Torch Cactus, Tree Cactus, Blue Columnar Cactus
  • Species: Pilosocereus pachycladus / Pilosocereus azureus
  • Genus: Pilosocereus
  • Home: Brazil
  • Natural habitat: subtropical or tropical dry forests
  • Height: can grow up to 10 m (33 ft); grows to the size of it’s space (so if kept in a pot, will stay small)
  • Flower: Funnel shaped; white with green or red
  • Blooms: April to July; summer; at night
  • Availability: Most common houseplant in the Pilosocereus family; large nurseries produce in bulk and sell wholesale

The blue torch blazes

The Pilosocereus pachycladus aka Pilosocereus azureus aka Blue Columnar cacti are endemic to Brazil. (Endemic means defined to a single geographic location.) It belongs to the Pilosocereus family. Pilosecereus means “hairy cereus” in latin – the perfect name for this cacti family because of their gold-tinted spines.

The Blue Columnar is, in fact, the most commonly cultivated species from that family. Large nurseries often grow these in bulk year-round and sell them wholesale. Because of their large size and need for warmth, they have to be grown in greenhouses. I love the fact that nurseries and greenhouses are growing these azure beauties, because their natural habitat is threatened by habitat loss.

Blue Columnars add a dynamic splash of colour to any gardener’s landscape. All you need is the correct climate and enough space! They also make great potted plants, as they’ll grow to the size of the planter.

Blue skies ahead

I’ve already mentioned the Pilosocereus pachycladus’s beautiful turquoise colour, which is what drew me to this columnar cactus. There’s more to it than that though. It can grow to a towering 12 feet tall and four feet wide out in the wild. Some websites I read say they can grow to 33 feet tall, giving trees a run for their money. Like trees, the Piloscereus pachycladus has a trunk with bluish-silver branches. Domesticated versions grow into the space they have available – so if they’re in a pot, they’ll grow as big as the pot will allow.

Since it is a cactus, the Pilosocereus has spines. They’re golden at first, and turn grey with age. In fact, as the blue columnar grows, its blue colour deepens for an even more vibrant appearance. It also flowers every summer. The tube-like white flowers have green or red outer segments and grow fleshy fruits.

The bigger the cactus, the bigger the flowers. When pollinated, the flowers develop fleshy fruit in a deep maroon colour. So it’s well worth it to let your Pilosocereus pachycladus grow as big as possible so you can reap the benefits of the sweet fruit.

A True Blue Cactus

The Pilosocereus pachycladus is a fast growing, low-maintenance cactus that loves sunning on the windowsill. It will stay indoor-sized for years before it needs to move into a roomier pot. There are still a few things to remember when caring for your blue columnar cactus.

I’m going to outline the main growing and care points here. If you need more detailed instructions or have more questions, Plantophiles’s “Blue Torch Cactus Care Guide from A to Z” is fantastic.

Turns azure in the sun

This columnar cactus loves the sun. Give it bright indirect sunlight, or even better, full direct sun. The more sunlight it drinks up, the bluer it gets. Aim for eight to 10 hours of sunlight a day. All that being said! It can handle low light if that’s all you have available. Four hours of sun is the absolute minimum it needs.

Just remember that it will be a bit paler with less sun. Here are a few things to watch for if you’re worried your Pilosocereus pachycladus isn’t getting enough sun:

Thinning or distorted trunk – it grows towards the light, so if it’s not getting the minimum amount of light it needs, it’ll stretch towards it.

  • Greener than it should be – while most cacti are supposed to be green, this one isn’t. If it turns green or is discoloured at all, that’s a sign it needs more light.
  • Rotting roots – if the soil is wet for too long, then the roots could rot. Root rot is also a sign that the soil and cactus isn’t getting enough sun.
Thrives well in the warmth

A very hardy cactus, the Pilosocereus pachycladus can survive in temperatures as low as -1°C, which is pretty good for a cactus! It’s natural habitat is very hot, desert-like even, so it can handle temperatures in the triple Fahrenheit digits, so over 40°C. It prefers heat and thrives in dry to average home humidity.

Like all cacti, the blue columnar hibernates in the winter. If it’s outside, it needs to be protected from winter frost with burlap, frost blankets or bed sheets. Regardless of if it’s outside or inside, help it go dormant by reducing the amount you water it in the fall.

Clever Cactus - Blue Columnar
Gets thirsty once a month

Speaking of watering! The blue columnar loves desert-like conditions. So you don’t need to water this bad boy too often – about once a month in the winter and once a week or every two weeks in the summer; or wait until the soil is completely dried out. You can test if it needs more water by pinching the blue-skin gently. A well hydrated Pilosocereus pachycladus has a firm body. If it’s soft and bouncy, it needs a drink. As I mentioned above, it needs less water in the winter.

When watering, you should pour slowly and evenly until water comes out the drainage holes. Toss out the excess water – don’t let it sit in its own juices! You can also water around the pot instead of directly on the cactus. This method encourages the roots to spread out and anchor the plant.

Prefers fast-draining soil

Sandy, fast-draining soil is the Pilosocereus pachycladus’s favourite bed. If you plant it in a terracotta or clay pot with cactus-specific soil, then the blue columnar will love you forever. You can make your own soil by combining two parts perlite, one part sand or gravel, some limestone and some organic matter. Double check your soil drains properly before potting your cactus by pouring water into it and making sure it goes right through.

Doesn’t need to eat much

Fertilizing this fast-growing cactus isn’t necessary. Giving it a bit of food won’t hurt it though – if you want it to become a giant, give it a bit of fertilizer every few weeks during the growing season. Dilute your fertilizer and use a balanced 20-20-20 product to make sure you don’t burn it.

If you’re not a fertilizer fan, you can add a little compost or vermicast to the soil. If you have a potted blue columnar, you should repot it every two years to replenish the soil nutrients.

Give it a new pot

Repotting every two years is the best option for your potted Pilosocereus pachycladus. If you don’t, not only will it eat up all the nutrients in the soil, but the pot itself will restrain its growth.

Here are some tips on how to repot your blue columnar:

  1. Repot only when the soil is completely dry.
  2. Remove the cactus from its pot. Use tongs or wrap it in newspaper or a blanket to protect your hands from the spines.
  3. Knock the soils away from its roots.
  4. Prune any rotten or dead roots.
  5. Place it in the new pot and fill it with cactus soil.
  6. Don’t water it right away; wait a week then give it a splash of water.

The blue columnar has extensive, fibrous root systems that don’t penetrate deep into the ground. They don’t mind being root-bound. Your new planter should be half or twice as small as the plant – this will keep it from getting overwatered.


Common Pests and Diseases

Pilosocereus pachycladus don’t have many serious pest or disease issues, which is great! And what makes them so easy to keep around. There are still a few things to watch for when growing your own, to make sure it survives until it’s your favourite azure tree.

Mealybugs – these tiny pests munch away at every part of the plant. If you spot them feasting on your blue torch, brush or high-pressure wash the cactus to remove as many of the bugs as you can. Then treat it with an insecticide until the mealybugs go away.

Root Rot – a common problem for all cacti. Root rot is what happens when you overwater a cactus. The roots become black and very soft. To fix it, let the soil dry completely. Then cut away the rotten roots and replant it.