Christmas Cactus--mold or mineral build-up?

[tomo]

My parents have had this Christmas cactus for about 10+ years and it blooms every December like clockwork! I was watering it recently and noticed this sort of white mold/build-up near the base of the plants...then I started looking at the leaves and noticed some of them looked a bit puny--some are a bit pale and some leaves have some spots. Now that I know about this amazing Cacti Forum I thought I'd ask about it...what is it and how can I treat it?

Thanks in advance!

[greenknight]

Looks more like buildup of salts to me - have you ever leached out the soil?

[Steve Johnson]

Looks more like buildup of salts to me - have you ever leached out the soil?

I concur -- bicarbonate buildup from hard water. Best remedy is to flush the mix with rainwater or distilled water. Most general-purpose container growers recommend doing it 3 times with 1 hour between each flush, although I don't know if we cactus folks need to go quite that far. And when we say "flush", that means let the pot drain all the way through like a running faucet. Tomo, if your Christmas cactus hasn't started its growing season yet, hold off until the plant is ready for it. Then if you have to water from the tap, you should really start getting in the practice of acidifying it. 5% white vinegar from the grocery story is perfectly safe for home use. Not sure how hard your tap water is, but I believe 2 tsp. vinegar per gallon should be okay. Even with that, I'd recommend flushing your pots once a year in the growing season.

[tomo]

Thanks for the info greenknight and Steve--we do have hard water here, so that makes sense. (Until I started reading this forum a few months ago, I had no idea that watering with tap water was such a no-no!) I looked at the planter and it has no drain hole! I'm thinking I need to repot it--should I repot it, give it a week or two to adjust, and then try to flush with distilled or rain water? Or should I try to remove the build-up before repotting?

[Steve Johnson]

I looked at the planter and it has no drain hole! I'm thinking I need to repot it--should I repot it, give it a week or two to adjust, and then try to flush with distilled or rain water? Or should I try to remove the build-up before repotting?

Can't flush without a drain hole. Repot the Christmas cactus immediately using the same routine I described for your golden barrel -- clean the roots as thoroughly as possible, soak in 1% Hydrogen peroxide for 15 minutes, gently rinse in running water, let the roots dry out, then repot in fresh, dry mix. I have zero experience with jungle cacti, so I don't know if yours is in the growing season yet. If so, give it a good drench 2 weeks after repotting. If not, wait until you see signs of new growth, then start watering. With fresh mix in the pot (and please make sure you have one with a drain hole!), it'll take quite awhile before salt buildup becomes a problem, so there's no point in flushing the pot right away. Of course watering with rainwater is the best if you can do it all the time, otherwise acidify your tap water, and do your annual flushes in summer.

[tomo]

Thanks for the advice. I bought a new pot today (and made sure it had a drain hole! ) and plan to follow that procedure & repot ASAP. I think I see some signs of new growth, so thanks also for the tip on when to start watering. My parents think it was last repotted about 5 years ago so we're all hoping this will help it stay nice and healthy for a long time.

By the way, I'm curious, how does flushing help a cactus? Does it get rid of all the impurities that have accumulated in the soil? I'd never heard of that technique before, very interesting! Honestly I learn so much here, thanks to you all!

[Steve Johnson]

I'm curious, how does flushing help a cactus? Does it get rid of all the impurities that have accumulated in the soil?

Yep. Aside from bicarbonates in hard water, fertilizer salts can also build up in the soil. The roots of all container-grown plants need occasional flushing of the pot to keep them healthy, and cacti are no exception.

[greenknight]

Absolutely. If you water the recommended way, you use enough that some comes out the drain hole, and you dump out the excess that came through. This gives the soil a little bit of a flush with each watering, which helps to slow the accumulation of salts - but more thorough flushing is still needed periodically.

In a pot without a drain hole, every bit of salts in the water and fertilizer that goes into it will remain in the soil or in the plant. You've seen the results.

[Steve Johnson]

Absolutely. If you water the recommended way, you use enough that some comes out the drain hole, and you dump out the excess that came through. This gives the soil a little bit of a flush with each watering, which helps to slow the accumulation of salts - but more thorough flushing is still needed periodically.

Good discussion, and it prompts me to revisit a topic regarding the connection between acidified water and fertilizers I posted on the Cultivation forum a few years ago. Since tomo is neither the first nor the last beginning cactus grower who could use some education on this matter, I may post a new thread so I can pass along what I've learned. There's nothing complicated or difficult to understand here, just a matter of putting it in the right words -- we'll see if I'm up to the job for the benefit of our beginners.

[tomo]

Whoa--so the reason we are supposed to use a pot with a drain hole is not only so the excess water can drain, but also so salts don't build up in the soil? That is amazing! And something I'd never heard of before, but it does make sense. So the combination of hard water + no drain hole led to the build up on the Christmas cactus. That's really good to know, and now I know how to fix the problem and hopefully prevent it.

Steve, I think a thread like that would be most helpful for me & other beginners!

Thanks again to you both for your helpful insight! I'll have to post a update once I've transplanted it.

[tomo]

Just wanted to give an update (albeit a few months late) --I transferred the Christmas Cacti to a new pot, new soil mix, etc. and it has been growing like crazy! This is a photo of it in April, it's grown even more since then.

[greenknight]

Looks like a happy plant.