Spongy cactus with healthy roots

[abhikjha]

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.

Spence, it is to let you know that I have decided to repot all my cactus including melocactus and Discocactus with your suggested approach of potting mix. I hope they all will thank you for this soon

[abhikjha]

One question though - if I use only Pumice, Perlite and Gravels, I hope this is even better. For fertilization, I will be using osmocote slow release granuels. Hope this is ok.

[Steve Johnson]

One question though - if I use only Pumice, Perlite and Gravels, I hope this is even better. For fertilization, I will be using osmocote slow release granuels. Hope this is ok.

I've been successfully growing cacti in a 60/40 pumice and granite gravel mix for 9 years, so I think you should do well -- compared to soil-based mixes, open aeration in a soil-less mix leads to better root growth. Because I use a liquid fertilizer, I have to fertilize my cacti every time I water them in the growing season. Your Osmocote granules eliminate that problem, although I don't have any experience with slow release ferts, so I'm not sure if this is the best approach over the long run. Whether it is or not can be determined only through your own experience. May take a few years before you know for sure.

By the way -- since you have access to pumice, why are you including Perlite in your mix?

[abhikjha]

Thanks a lot Steve! Instead of osmocote, I can use liquid fertilizer too but not sure which one to buy! I noticed you use Dyna Gro but it's unavailable in my country. Instead I was thinking to use NPK 8 25 25 diluted to quarter strength maybe once a month. I have also mixed my potting mix with Seaweed granuels for micronutrients and bonemeal for good growth of roots along with systematic fungicide. All this in addition to osmocote.

The reason I am using perlite is because I am using relatively smaller pots (3 inch for most of my plants, few larger ones in 4 or 5 inch) and since the size of pumice available here in India is often too big, it becomes difficult to fill the pot to cover roots. So for that purpose alone, I am using perlite as it's easy to fill the pots surrounding roots. However, majority of the pot is filled with pumice only. To avoid perlite floating to the top, I then cover it with gravel or stone.

I also noticed that I need to acidify my soil as well. So am planning to use white vinegar maybe once in a month or so.

[Steve Johnson]

The reason I am using perlite is because I am using relatively smaller pots (3 inch for most of my plants, few larger ones in 4 or 5 inch) and since the size of pumice available here in India is often too big, it becomes difficult to fill the pot to cover roots. So for that purpose alone, I am using perlite as it's easy to fill the pots surrounding roots. However, majority of the pot is filled with pumice only. To avoid perlite floating to the top, I then cover it with gravel or stone.

Okay, that does make sense and you're on the right track there.

Instead of osmocote, I can use liquid fertilizer too but not sure which one to buy! I noticed you use Dyna Gro but it's unavailable in my country. Instead I was thinking to use NPK 8 25 25 diluted to quarter strength maybe once a month. I have also mixed my potting mix with Seaweed granuels for micronutrients and bonemeal for good growth of roots along with systematic fungicide. All this in addition to osmocote.

Unfortunately the liquid fertilizer you have in mind is way too high in P and K. The ideal NPK ratio for cacti and succulents is 1:0.4:1.5, so 8 3 12 would be the right balance. It's a shame that you can't get Dyna Gro ferts, because the true NPK element values of the All Pro 7 7 7 and Orchid Pro 7 8 6 are close to ideal. (All I need to do is supplement the 7 7 7 with a little Potassium sulfate.) If you have a background in chemistry, you could make your own fert, but for those of us who are chemistry-challenged, we have to make do with whatever is commercially available. If you can find a fert with a balance that's at least close to what we're aiming for, let me know, and I'll suggest the proper dilution rate. Seaweed granules for micronutrients are fine, but stay away from bone meal -- maybe fine for nonxeric plants, but all it does is add even more P. Good, healthy root growth in cacti and succulents comes from a higher proportion of K to N. We need less P, not more.

I also noticed that I need to acidify my soil as well. So am planning to use white vinegar maybe once in a month or so.

Acidification is required only if you're watering with hard tap or well water. If you're watering your plants with rainwater, you shouldn't need to acidify. Depending on how far you want to go, the following may be useful:

http://www.cactiguide.com/forum/viewtop ... 25&t=43525

Thanks a lot Steve!

You're most welcome -- glad to help whenever I can!

[abhikjha]

Thanks Steve. Your suggestion on bonemeal is really helpful.

I tried searching for NPK 8 3 12 or in similar denominations but couldn't find anything atleast online. Will keep searching for it. Meanwhile, what's your view on compost(using vermicompost) tea with low diliution to given with every watering? Heard great results of this on plants.

[Steve Johnson]

I tried searching for NPK 8 3 12 or in similar denominations but couldn't find anything atleast online. Will keep searching for it. Meanwhile, what's your view on compost(using vermicompost) tea with low diliution to given with every watering? Heard great results of this on plants.

My only experience is with the Dyna Gro 7 7 7, so I had to investigate what the NPK values for compost tea should be. Here's what I found:

https://www.gardenmyths.com/compost-tea-npk-values/

Not promising, is it? Osmocote makes a slow release fertilizer formulated specifically for cacti and succulents, so that may be your best option. One of our members in Australia (and he's a professional horticulturalist, by the way) is doing well with it, so you may want to find out if you can get it in India. As a point of interest, you can find Dyna Gro 7 7 7 at Amazon India. Price is 15,116 rupees -- equivalent to $200 US. YIKES!

[Steve Johnson]

Hold the phone...

Well, I just did some research at the Amazon India website, and I may have found the perfect liquid fert for you:

https://www.amazon.in/SS-13-05-26-Ferti ... 25&sr=8-79

The N-to-P ratio is good, and while the N-to-K ratio is higher in K than what I recommended, I don't think that would be a problem. Dilute at quarter strength. Just a reminder, though -- when you're growing cacti in a soil-less mineral mix, this is an essentially hydroponic approach, so you'll have to fertilize every time you water.

[abhikjha]

Oh wow! Thanks a lot Steve! Really appreciate it that you took the time to find this for me

Going to buy this asap.

[Steve Johnson]

Oh wow! Thanks a lot Steve! Really appreciate it that you took the time to find this for me

You're welcome!

Something I did want to mention -- when people talk about how much they're diluting their fertilizers, terms like "half strength" and "quarter strength" don't mean much unless we know what's indicated on the fert's label. In my case, the Dyna Gro 7 7 7 indicates full strength at 1 teaspoon per gallon of water, so I'm diluting at half strength, which is 1/2 tsp. 1 US gallon = 3.8 liters, and my guess is that you're watering with a 4 liter jug. If that's the case, correct dilution of the liquid fert you'll be getting is 1.3 milliliters per 4 liters of water.

Happy growing, my friend!

[abhikjha]

Thanks again Steve! Now the tricky part would be to measure 1.3 millilitres ...

btw, I have one question on the sunlight requirements - due to position of sun which has moved upwards, my South facing window is no longer getting direct sunlight for extended period, so I have put most of my plants in direct sunlight in open without any shade (here they get sunlight for 3-4 hrs). They seem to be doing fine. I mainly have collections of Astrophytum, Melocactus, Gymnocalycium plus some other plants. What I understand is that Astrophytum (except Asterias) can take full sunlight but Melos and Gymnos need proper shade. Is that correct?

[abhikjha]

What a bad luck about timing! With rising COVID cases due to second wave in India, Amazon has been instructed to deliver only essential items and this doesn't fall in essentials .. So now my plants have to wait when this madness gets over..sigh!!

[Steve Johnson]

I have one question on the sunlight requirements - due to position of sun which has moved upwards, my South facing window is no longer getting direct sunlight for extended period, so I have put most of my plants in direct sunlight in open without any shade (here they get sunlight for 3-4 hrs). They seem to be doing fine. I mainly have collections of Astrophytum, Melocactus, Gymnocalycium plus some other plants. What I understand is that Astrophytum (except Asterias) can take full sunlight but Melos and Gymnos need proper shade. Is that correct?

Not sure about Gymnos, but Melos do need proper shade to avoid sunscorch.

[abhikjha]

Hi Guys, wanted to share an update on this one. This mammillaria un-pico literally grew leaps and bounds after changing the substrate to pumice and gravel as suggested by experts here. Given I am in tropical climate, here is a proof that cactus do grow in our climate if basics are right. Thank you once again for guiding me.
Here is the pic, left was in April 21 and this is in Sep 21. Pot is same.

[greenknight]

Good to see - it looks happy now!