Spongy cactus with healthy roots

[abhikjha]

Hi all,

I am new to cactus growing. I live in Mumbai, India. Recently, in one of my cactus Mammilaria Unpico, I observed that it is not firm (rather it's spongy). Since, I watered it few days ago, my immediate concern was rot, so I took it out of wet pot, roots looked fine to me (pics attached). Nonetheless, I treated it with H2O2 and fungicide, kept in a shady but ventilated area for a day and then potted it in a dry soil. I haven't given water since then(around a week) and it has been kept on South facing window. But it still hasn't gotten firm as yet. Is this because of underwatering?

Please help me in saving the plant.

Images:
https://ibb.co/KNk6CCy
https://ibb.co/rFRDS1W

[The_Nikon_Guy]

I too had the same issue of spongy cactus but very healthy roots. I think in my case, I kept the cactus too dry for too long and therefore was taking a verrry long time to develop hair roots for absorbing water/nutrients.
My solution to this was to use hydroponics and rejuvenate the root system. It worked well for a month and then when I went to put the cactus back into the soil it shrivelled up a bit initially and then recovered quite nicely.
The big assumption here is that you do NOT have any existing rot on your root system

[The_Nikon_Guy]

Another reason cactus gets spongy is due to application of too much Nitrogen. Generally for cactus I use a 2:10:10 raio (NPK) mix.

[abhikjha]

Thanks a lot for the reply.

I actually bought this cactus online so the seller actually sent bare root which might have caused this issue.

By hydroponics you mean growing root in water?

May I ask how long you kept the plant dried which caused this problem. My biggest conundrum with cactus care is watering. It's actually headache

Further, I want to know if below substrate is good for growing cactus:
1. River sand - 30%
2. Dried vermicompost - 30%
3. Perlite - 20%
4. Pumice - 20%

I also add fungicide, seaweed granuels and bone meal into the substrate.
Do you recommend any changes in this? It will be very helpful.

[greenknight]

The main problem with this cactus is it it doesn't have enough roots. It must have lost a lot in the shipping process. Not a major problem, it will grow more. I don't think it needs the hydroponic treatment. To do that, it's best to suspend the cactus above the water so only the roots are immersed, not really possible with this one.

The small root system creates a difficulty, though - the volume of the pot should be only a little larger than the root ball, but any pot that this cactus would fit in would be much larger than that. The mix in the bottom of the pot would stay wet too long and go sour. The solution to this is to put some large stones in the bottom of the pot to take up the extra space. Work some potting mix down between and around the stones, then pot the cactus on top of that. That way, you avoid having a lot of wet soil in the bottom of the pot that the roots can't reach.

I do see problems with your potting mix:
1. Sand - fine sand is not good. Unless it's very coarse sand, don't use it at all.
2. Vermicompost - good stuff, but you're using far too much for cacti. Too much nitrogen. Reduce that from 30% to 10%.
3 & 4. Perlite and Pumice - they're fine, and basically interchangeable. You can use one or the other, or both, it makes little difference. They do hold some water, though. In a humid climate like you have, you need a very free-draining mix, they may hold too much water. I recommend adding some non-porous fine gravel to your mix (not limestone).

S my suggested mix would be more like:
1. 10% vermicompost
2 60% Perlite and/or Pumice.
3. 30% gravel.

Not to say this is a perfect mix, just a suggestion. Even more gravel might be better. Anyway, with a more gritty, open mix like this, you won't have much risk of overwatering, and your cacti will produce much more vigorous root systems.

[7george]

For many cactus species is normal to be soft during the winter or rest period. Just wait more for the summer or the active growing period.

[abhikjha]

Thanks guys!! Really glad to see your replies. I took a chance to water it to see if firmness returns, and was happy to see that a bit of firmness has returned. I guess with regular watering, it will return to its full firmness and as George mentioned, it may return to full shape in growing period.

@greenknight : Thanks so much for your advice on the soil mix. I will follow that for few of my existing and all new plants. Just had one query: I have seen many articles, even on Cactiguide that people advice to use cococoir, topsoil in limited proportion to retain some moisture otherwise in full gritty mix, water will drain away too quickly without fullfilling the water requirements of cactus. Since I am not using these for my plants, referring these articles, I opted for sand (it's a bit coarser but not stony or pebbly) so that after watering, substrate remains moist for 1-2 days. Am I doing something horribly wrong? Please advise as then it means I will need to repot all my plants

[greenknight]

7george has a good point. You don't really have a winter in Mumbai, though - but your cacti still need a resting period. Here's a thread where the subject is covered in more detail:
http://www.cactiguide.com/forum/viewtopic.php?t=38323

Mammillaria spinosissima cv. Un Pico is the full name of your cactus, by the way. The species is native to the mountains of central Mexico, 1600-1900 meters above sea level, so it would undoubtedly like a cooler dormant season than you can provide. It may never flower in your climate, but it's mainly grown for its unique form, anyway.

You need to adapt your soil mix to your climatic conditions. Where it's very humid it's best to use a mix that doesn't retain too much moisture, but if they're drying out in a few days (not just the surface, but deep down) they'll be okay.

You can grow cacti in anything if you get the watering right, but it's harder to get it right if the soil holds too much water. I was estimating what would be a good mix for you based on information I found about the Mumbai climate, you might need to adjust that to suit your needs. Try it out with a few plants and see how it works.

If the sand is fairly coarse, it can be used. If it contains any fine, powdery material, though, that should be sieved out. The fines have a tendency to works their way down to the bottom of the pot and clog up the pore spaces there, which interferes with drainage.

[abhikjha]

Thanks a lot Spence for the detailed ID of the plant. It will be sad if it doesn't bloom though. At present, few of my plants have bloomed, mainly Gymnocalcyium and Echinopsis. But I guess since I bought these plants very recently from online seller who is based out in northern part of India where we do have 2-3 months of winter season, so I guess they had winter rest before I bought them.

My main worry is rainy season. In Mumbai, it rains heavily for 3 months. I am planning not to water these guys or water very little in those 3 months and since they are indoors, they won't be exposed to extended rainy season. Let's see how it goes.

Also, thanks a lot for your comments on potting mix. I think I will use your suggested mix for all my plants in phase wise manner.

I had a further question, do you think in nights here, since it doesn't get too cold which may affect their photosynthesis process, besides fan which runs for entire night with open window through which we get nice breeze, I should keep my Aircon on for few hours (with windows open) to make it cooler?

[greenknight]

You might want to check out the advice from this grower in Manila, as well: https://www.philstar.com/lifestyle/mode ... ti-tropics

He does a good job of explaining the issues you face - the climate there is quite similar. He doesn't use quite as much grit in his potting mix as I suggested, except perhaps for the most wet-sensitive species. He also lists some tropical genera that should do well and have a better chance of blooming well in your climate (Gymnocalycium is one of those).

[abhikjha]

This is a brilliant article! Exactly what I was looking for. Thanks so much Spence for sharing it. Not sure whether we have him on our forum ..

[greenknight]

Your welcome. Also, I meant to say that running the Aircon with the windows open would just be a waste of electricity.

If it stays too hot at night, all that might happen is heat dormancy - the plants may just shut down and wait for cooler conditions. They'll stop taking up water if that happens, and you must stop watering to avoid rot. It wont hurt them other than that.

[abhikjha]

Thanks Spence! How much temp in night is too high for them to go in heat dormancy and also, how do you know if a plant has gone into heat dormancy? Are there any clear signs to observe?

[greenknight]

It varies somewhat, but you should watch out if night temperatures approach 20c/70f.

The main symptom is they stop taking up water. Where people get into trouble is, they think at higher temperatures the plants need more water. They continue giving extra water when the plant has stopped using any, and they drown it.

Every plant has a limit to how much heat it can take and keep growing, it's not just succulents. I've seen videos of corn fields that were irrigated until the soil was mud, but the corn was still drying up because it was just too hot. Cacti and other succulents are better equipped to survive those hot conditions, as long as they aren't over-watered.

[abhikjha]

Thanks Spence! Lowest it reaches here is 24C so higher than you mentioned..let's see how these guy fare.. I have very good ventilation though (large window with fan and since we are close to sea, very nice breeze), so I guess that could help them do CAM photosynthesis..Right now few of these guys are blooming (Gymnocalcyium, Thelocactus and Echinopsis). I understand that Melocactus will be more suitable in my climate so planning to buy few of these..