I think I've given home to Audrey III
October 30, 2013 8:46 AM   Subscribe

I have a cactus which I believe to be an ostropuntia subulata monstrose (pic of one that looks just like mine). It didn't grow for years, and now it's growing astonishingly quickly. Why? And what can I do to help it along? Any tips?

I bought it from a garden centre in 2010 or so, from one of those displays of small cactus that seem to be popular by the checkouts. It sat on my windowledge in West London (UK) for the next three years, but didn't seem to grow at all despite the aloe plant next to it seemingly thriving. When I moved out earlier this year, I wondered whether to chuck it as it seemed dead, but hung onto it anyway.

Since moving to our new flat in south-east London, it has grown like a weed. In six months, the main stalks have shot up three or four inches, and a new thick branch has grown off the side with another one coming in. Since moving it into our bathroom - which has no window - I'm noticing extra growth daily, with the first new branch getting thicker and growing longer spines.

Why is this happening, and what am I doing to help? Obviously the UK isn't a natural habitat for cacti, so it seems really strange. Will the lack of natural light harm the plant long-term, and also the use of the products we use to clean the bathroom?

Useful info:
- the old place had a dodgy roof, to the point that the wooden windowframe rotted away. I'm not sure which way the house faced, but it always seemed dark and dusty.
- Our new place is east-west facing - the cactus went on the kitchen windowsill where it got plenty of light, but it seems to really like the bathroom.
- Neither place had air-con, but both have central heating.
- It was repotted into a bigger pot three months ago, which is wider rather than taller. (I'm no horticulturalist, apologies for the vague description.) I didn't use cactus compost as I couldn't get any. At the same time, I potted some cuttings from my aloe plant. These have taken a few months to seem as though they are healthy and growing well - whereas the cactus has been growing like a weed, especially in the bathroom.
- I haven't given it any kind of plant food, just water when the soil seems dry.
- I was pretty miserable in the old flat - was the cactus doing some kind of magical realism trick where it didn't want to grow until I left?
posted by mippy to Science & Nature (10 answers total) 1 user marked this as a favorite
Response by poster: Also: When it was on the windowledge, it would bend toward the light. If I moved it the other way around in the morning - so it was bending toward the room rather than the window - by the time I arrived home in the evening, it had bent back. I've never seen a plant react so quickly to the light!
posted by mippy at 8:51 AM on October 30, 2013

It's probably getting more light now. Cactuses need huge amounts of direct sunshine to prosper.
posted by Chocolate Pickle at 9:03 AM on October 30, 2013 [1 favorite]

It's etoliating trying to find light. Which is a bad thing. A cactus must have lots of light. A South facing window is ideal but an east or west facing window that gets sun part of the day will do (but your plant will never reach it's full potential and you to need water less when there is less light).

You don't want cacti to grow fast. It makes them weak, prone to rot, disease and falling over.
posted by srboisvert at 9:04 AM on October 30, 2013 [1 favorite]

If there's no natural light in the bathroom, this is due almost certainly to the repotting. Long term, though, it will need bright natural light.
posted by Specklet at 9:05 AM on October 30, 2013

It got nutrients from the new soil (you really should weakly fertilize your cacti) and now has more strength to grow. Fresh soil has nutrients but plants exhaust the ones they need (which is one reason farmers rotate crops) and fertilizer helps slow the exhaustion down though eventually most all plants will benefit from new soil.

Agreed that if indoors in the UK, it should get the strongest, longest amount of daylight possible.
posted by vegartanipla at 9:10 AM on October 30, 2013

I'm in LA, so my tips won't directly translate, but--
I check the weather reports for Arizona. When it rains there, I water my cacti. Otherwise, I leave them in front of the brightest windows (east for me) and sort of ignore them.

Your cactus is growing frantically because it wants light.
posted by Ideefixe at 9:25 AM on October 30, 2013

Response by poster: So it's reaching toward the artificial celing light? The trouble is that we are heading for winter and there isn't a great deal of sun to be had in our climate. We don't have a south-facing window, or a balcony/windowbox.

So what I need to do is keep it on a windowledge, give it some food now and again (is Baby Bio OK?) and water sparingly?

I did notice it was becoming unbalanced in terms of the weight of the new branch - I was worried it would topple if it keeps growing.
posted by mippy at 9:32 AM on October 30, 2013

It might like a grow light, if you don't get lots of sun. Also, you don't want to put a cactus someplace damp.
posted by Ruthless Bunny at 10:24 AM on October 30, 2013

No food at all during the winter and water very lightly once a month until it is growing season again (next May roughly). It's just growing upwards because it has water and rich soil. Artificial lighting won't affect it much at all as it will be too far away to work as a light source (if you look at light grower setups for cacti and succulents the lights are set up as close to the plant as possible without cooking the plant. Inches not feet).

If the light is low you want the plant to go dormant. Zero growth.

One problem is that your soil mix is probably too nutritious for cacti. Some of my cacti growing friends don't even use soil. Just pure pumice and sharp sand. Cacti mix you buy in stores is pretty crap and you need to adulterate it with sharp grit at the very least.

Indoor growing is tricky because plants use three cues for growing - light, warmth and water/nutrients. It's hard to eliminate the warmth indoors unless you have garage or basement that isn't heated. Light is pretty low in England in the winter even with a southern exposure. So control the watering/nutrition as much as you can. It's a bit of balancing act because you need to keep the roots alive with some water but avoid triggering weak growth.

The particular plant you have is cheap and is a fastish grower for a cacti - it is often used as a stock plant for grafting because it is quicker and more vigorous than the plants collectors want to graft onto them.

Next time you want to buy a plant go to a BCSS show and see some fantastic and insane plants. You can get something 100X cooler for next to nothing and it will be properly potted up and last you a long long time.
posted by srboisvert at 10:28 AM on October 30, 2013

Response by poster: I've managed to get a photo of it via my tablet, which isn't the best for botany photography! On the right, you can see the new growth from the past six months. Where the 'main' part of the plant looks skinny is where it's shot up since moving house - there's about four inches' growth on there.
posted by mippy at 3:27 PM on October 30, 2013

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