Discocactus root issues

[Salazar]

Good day!

So I've had this plant for only a few months, it had been growing well, much better than I thought it would, until recently when I noticed it felt loose in it's pot and sure enough a light nudge dislodged it.

So does anyone have tips helping a mature Discocactus regrow it's roots?

Most of the stuff I've encountered so far has stated that mature Discocacti don't tend to do well against root loss but I'm hoping I can save this one. It's my first mature Discocactus and even has buds on so it'd be quite a shame to loose this one.

Thanks!

[Steve Johnson]

Good day!

So I've had this plant for only a few months, it had been growing well, much better than I thought it would, until recently when I noticed it felt loose in it's pot and sure enough a light nudge dislodged it.

So does anyone have tips helping a mature Discocactus regrow it's roots?

Most of the stuff I've encountered so far has stated that mature Discocacti don't tend to do well against root loss but I'm hoping I can save this one. It's my first mature Discocactus and even has buds on so it'd be quite a shame to loose this one.

Thanks!

Photos would help. Also, what species is it? If it's D. horstii, it's the most difficult Discocactus to grow.

[Salazar]

Thanks Steve!

It's a Discocactus zehntneri, apparently on the easier side of the spectrum from what I've read.

Here's some photos

IMG20230529084444_copy_800x800.jpg (238.97 KiB) Viewed 2360 times

IMG20230529084504_copy_800x800.jpg (180.15 KiB) Viewed 2360 times

[7george]

Was the soil dump? Try to sterilize a bit the roots and give this guy new soil. Not from the garden but clean mineral one.
The look is not hopeless.

[Salazar]

A bit damp yes, it's been very rainy the past two weeks.

It was in a mineral mix, the mix I use for the majority of my plants, the rest of my plants are fine though.

What would I use to sterilize? Alcohol? H2O2?

[Steve Johnson]

I'm going back to your "Obregonia advice" thread, so I just wanted to find out if this is the mix you're using for the Disco:

Well I don't have exact numbers for proportions but it's nearly purely inorganic material, volcanic rocks, pumice, quartz and silica granules and a tiny bit of garden soil.

And this is what you said about your fertilizer:

I don't really fertilize a lot. I'll occasionally put in a few pellets of a slow release fertilizer if I have it on hand, that's it.

If that's what you're still doing, it explains why the Disco has lost most of its roots. There's nothing wrong with your mix, and while it's not hydroponic in the strictest sense, it's close enough. Simply put, the plant needs to be fertilized a lot more often. A few pellets of slow release fertilizer won't cut it, so I recommend that you go with a liquid fert -- fertilize every time you water, although you can occasionally skip on the fert since you have a tiny bit of soil in the mix. If you're using a liquid fert and you're fertilizing often enough, let me know about its chemical analysis and your dilution rate.

[Salazar]

Ah so the root loss is a nutrition issue? I was thinking it was because of the nearly daily strong rains for the past few weeks or maybe it's both.

I've actually increased the organic matter and soil amount for this one and some of my other plants.
I only used very little for the Obregonia because I bought it early on when I was still pretty new and inexperienced and I was a very paranoid about it rotting haha.

[Steve Johnson]

I've actually increased the organic matter and soil amount for this one and some of my other plants.
I only used very little for the Obregonia because I bought it early on when I was still pretty new and inexperienced and I was a very paranoid about it rotting haha.

Organic matter and soil only mean that you won't need to fertilize as often as you would in a hydroponic mix. I'll explain that a bit later, but in the meantime -- there's no getting around having to fertilize cacti and succulents on a regular basis. I understand that time release fertilizers make the situation easier because they last for about 6 months before they need to be reapplied. Unfortunately, the only time release fert designed specifically for cacti and succulents is the one we can't get outside of Australia. I've been using liquid ferts ever since I built my current collection in 2011, but if you can't find one with the right nutrient profile (a problem you might have in the Philippines), look for a dry fert that's soluble in water. Basic rule of thumb for "ideal" NPK numbers in a fert -- P lower than N, K higher than both. If you don't mind going through a detailed discussion on the matter, read the following and you'll get a much better idea of the fert (liquid or dry) you should be looking for:

viewtopic.php?t=47603

Some people claim that any old fertilizer will do for cacti and succulents, but that's simply not the case. I wish it was easier if we could get ferts tailor-made for cactus and succulent growers, although when we review the products offered by manufacturers trying to do just that, I'm shocked by how little they know about what the plants really need for optimal long-term health and growth. If you can find a fertilizer that matches what you read in my presentation, let me know, then we'll see if you might need to supplement it.

Now we'll discuss something called cation-exchange capacity (CEC). Soils have relatively high CEC, which means that any nutrients not taken up by the roots stay in the soil once it dries out. When you water again, those nutrients are released back to the roots. Pumice has very low CEC and granite has none, so that's why I have to fertilize every time I water my cacti in the pumice-granite gravel mix I use. There's an upside and a downside to increasing the amount of organic matter and soil in your mix:

• Upside -- as I just said, you won't need to fertilize as often. My guess is that you'll be fine if you fertilize with every 3rd or 4th watering. (Maybe every 3rd watering for the Discocactus.)

• Downside -- increased risk of rot. However, I can only go by my local climate, so it may not be as much of a risk in your tropical one.

If you'd like to err on the side of caution and stick with your almost-hydroponic mix for everything (including the Disco), you can flip the fert-no fert routine around -- skip on the fert with every 4th watering.

For you the hard part will be taking the time to find a fertilizer that's as close to ideal as you can get. The next step will be to determine the right amount that should go into your watering solution (plus any supplements you may need). Once you have all that figured out, the easy part will be following a fert-no fert watering schedule based on the type of mix you're growing your plants in.

Your Discocactus certainly can be saved, but it won't happen unless and until you get a handle on the fertilizer issue ASAP. When you do that, it'll be better for the rest of your plants too.

[7george]

The interesting thing is that this cactus being under rains (or it was under shelter ?) is contracted so it is short of water. Usually at deficite of nutrients cacti and other plants take those from (parts of the) stems being killed for for that reason so we see there brown spots. Roots: that is unusual for me. Fertilizing make sense but is that the reason for dyeing roots? Not sure what is the problem, I just pointed what I would do seeing this with my plant.
Could be also some infestation from root nematodes if the organic part of the soil hasn't been sterilized before use.

[Salazar]

-It's not totally exposed, it's under the eaves of the house.

-Initially the shrinking wasn't concerning to me. Many new plants I buy do this. I find that if I buy from commercial growers that use a lot of organic matter and fertilizer in their soil and water more frequently their stems are very bloated so when I switch over to my mix more mineral mix in my growing conditions plants will usually shrink.
Though I admit this level of shrinking does seem usual.

-If it was nematodes idk how I would confirm that aside from the presence of root galls.

-Maybe it was just because of the very moist conditions that caused the root loss and since it was a new plant maybe it wasn't established enough to handle that? But then again it is a tropical species so I assumed it could handle moisture better than other species.

[Steve Johnson]

Before I pursue this further, have you fertilized the Discocactus at all since you got it a few months ago?

[Salazar]

I had yes, I mixed in some slow release fertilizer along with the organic matter I added.

[Steve Johnson]

I had yes, I mixed in some slow release fertilizer along with the organic matter I added.

Okay, then maybe you don't have a nutrient deficiency problem after all. Sorry, but I'm stumped.

[Salazar]

I very much appreciate the effort to help though.

Maybe it's just one of those things that happens y'know? Like in the past some of my Stapeliads, Edithcolea especially, just randomly loose their roots with no apparent significant change to their environment.

Well then if we can't find a cause I'll just have to focus on recovery then. It's such a small plant, hope it pulls through.

[Steve Johnson]

I very much appreciate the effort to help though.

Maybe it's just one of those things that happens y'know? Like in the past some of my Stapeliads, Edithcolea especially, just randomly loose their roots with no apparent significant change to their environment.

Well then if we can't find a cause I'll just have to focus on recovery then. It's such a small plant, hope it pulls through.

I hope so too -- your tropical climate should be perfect for Discocactus, and Melocactus as well. And maybe I shouldn't give up so quickly here -- please give me the chemical analysis of the slow release fert you're using. Evaluating fertilizers is an important part of what I can do, and given the tremendous learning I got from MikeInOz, I'll be able to see if your fert is the right one for cacti. Bear in mind that many desert species are remarkably tolerant of fertilizers which really aren't the best, but some species are remarkably intolerant, so I have to wonder if your Disco is one of those. If it is, time to rethink your fert.