When Cactus Turn Yellow

[pone]

In general, is a cactus turning from green to yellow a sign of nutrient deficiency?

Assuming that you start to add Dyna Pro 7-8-6 to every watering of the cactus, how long should it take for the yellow to disappear completely? I have two sister cactus, and regular fertilizing managed to get one of the two about 70% back to green. The other plant is stubborn and remains yellow with hints of green. I am starting to worry that I am not going to get the plant back to health before winter comes.

Planted in pure pumice, is it unreasonable to water a cactus twice a week in the hot summer sun? And fertilize it once a week?

[Caudexguy99]

Posting a picture would help with diagnosis. Yellowing can sometimes be a sign of rot or sunburn also.

[pone]

I had rot problems with both of the cactus below, which I attribute to the fact they were nearly completely yellow and very starved for nutrients. They were just weakened by that. I cut off the tops and they seem to have survived.

The first plant is doing better, having returned in its base section to almost green, with some stubborn yellow sections in the folds of the cactus. The second plant looks much worse to me. It has yellow throughout that persists, and there are sections where it looks like rot wants to get started (superficially on the surface, not at the core).

In any case, not sure how these photos address my original question. I was asking - IN GENERAL - if a cactus is nutrient starved and has turned yellow from that, how long should it take to completely reverse the yellowing after you start to fertilize at each watering (at least once a week)?

2020-06-16 19.47.48 (Custom).jpg (62.12 KiB) Viewed 3786 times

2020-06-28 18.19.28 (Custom).jpg (85.68 KiB) Viewed 3786 times

[mikethecactusguy]

I just want to add that I have a few plants that new growth appears it is much lighter in color. looking at one of my oldest, 20 years and all the growing tips a bit yellow at first. The plant is not nutrient deficient . During this growing season I always water everything with a 25% solution of Cactus Juice.
looking at your photo's it appears to be only on one side. Sunburn?

[pone]

@theclosetguy No, the entire plant was yellow, both front and back. Regular fertilization brought it to the current state. Now it is about the same amount of yellow on both sides.

[pone]

@theclosetguy I looked up some photos of sunburn on cactus. The images I found look more like a tar paper texture on the surface of the cactus. My cactus have a deep yellow pigmentation within but the surface skin is fine. The following photo is an example of sunburn that I found online.

cactus-sunburn-01 (Custom).jpg (77.27 KiB) Viewed 3767 times

[mikethecactusguy]

Sunburn usually starts with just a lightening of the surface. Removed from sun the surface will revert. left out it than burns more.
If nutrients helped to reduce the yellowing probably time will also. These babies all require patience. We must learn from our mistakes. A few soldiers will be lost in the process. We just hope those lost are not the expensive one.

[pone]

@theclosetguy Interesting, so while they are recovering from their malnourished state, maybe I should be moving the planters into a place that only gets morning sun? I am probably making the plant commit too much energy just to survival by putting them in full sun.

[Steve Johnson]

Hi pone,

That's the 2 Cereus peruvianus monstrosus you posted about back on December 15. Let's do a before-and-after comparison here -- first, plant #1:



The new head does look good. Re. plant #2, you're making more progress than you may realize:



Considering how nutrient-starved it was, plant #2 is greening up nicely, and I think the yellow patches will turn green with regular applications of water and fertilizer in about a month. The new growth on one of the ribs looks pretty good, although I wonder why you were having problems with rot on the part of the stem you chopped off. Nutrient deficiency usually doesn't cause rot, so there could be something else involved. It's difficult to do a remote diagnosis, so unfortunately I can't give you any ideas on what happened.

Planted in pure pumice, is it unreasonable to water a cactus twice a week in the hot summer sun? And fertilize it once a week?

In a hot, arid climate watering every 4-5 days in summer would be reasonable. However, the San Francisco Bay area has a humid climate, so if I were you, I wouldn't water cacti any more often in summer than I do in the spring. Rule of thumb with all soil-less mixes (including pure pumice) -- fertilize every time you water in the growing season.

[pone]

@steve_johnson, okay I will try to be optimistic.

[mikethecactusguy]

Nice Call Steve. good Sleuthing

[pone]

@steve_johnson, would you cut off the healthy-looking top growth on the second plant? That might be my only shot at getting a totally normal looking plant out of this.

[Steve Johnson]

@steve_johnson, would you cut off the healthy-looking top growth on the second plant? That might be my only shot at getting a totally normal looking plant out of this.

Yes, I would. Although I don't know the species well enough to be sure, my gut feeling tells me that Cereus peruvianus roots rather easily. Cut the new head right at its base -- be sure to use a sharp knife and sterilize it with alcohol first. (You may already know that, but I mention this just in case.) Give the freshly-exposed surface a liberal dusting of sulfur powder as a barrier against mildew or fungus that could lead to infection. Give the surface plenty of time to callus over, then put the plant in its own pot with dry pumice. If you haven't rooted cactus cuttings before, I can give you some further guidance.

By the way -- since plant #1 still has a rooted base, you can use it to grow more heads for propagation. Hopefully plant #2 will grow a new head too, in which case, you'll know what to do.

[pone]

@steve_johnson, okay, so what I have at this point is two factory plants, to turn out new plants.

Can I use rooting hormone on the cut cactus base? I guess that will not substitute for sulfur, and doing both is problematic although I could mix the two powders together before applying.

I have limited experience rooting cactus. What I have been doing is planting in pumice, then putting it into the shade, and I water maybe once a week. It sometimes takes more than six months to form roots.

[Steve Johnson]

Can I use rooting hormone on the cut cactus base? I guess that will not substitute for sulfur, and doing both is problematic although I could mix the two powders together before applying.

I've never found any use for rooting hormone powder, so go with sulfur powder. If you don't already have it, sulfur powder is easily available at any nursery or big-box garden center.

I have limited experience rooting cactus. What I have been doing is planting in pumice, then putting it into the shade, and I water maybe once a week. It sometimes takes more than six months to form roots.

Without roots, cacti don't have a way of taking up water, so there's no point in watering yet. Check the base periodically and wait until you see the presence of new root stubs. When you do, apply light watering -- sip, don't soak. This "teases" the roots into growing more as they seek out water. My approach is to lightly water the mix every week or two for a month, then check to see if the plant is grabbing into the pot. Once it grabs in, I'll increase the amount of water to something between a sip and a soak for another month, then deep watering after that. Watering frequency is the same during this process, so gradually increasing the amount is what will lead to a successfully-rooted cactus.

The new head appears to have plenty of healthy material, so don't be discouraged if it doesn't start rooting until next spring. I've seen cuttings look like they're at death's door in winter, only to have them bounce back with new roots in the following growing season -- the best thing to do is be patient. But regardless of whether or not the cutting has rooted by the end of summer, I'll recommend that you protect it from the rain during wintertime.