Rot or Not? Please help

[CoolestGravy]

Duly noted. And I'll keep reading and see what else I may find. While being cautious of BS, of course.

Steve, I can't thank you enough for all your help

[Steve Johnson]

Duly noted. And I'll keep reading and see what else I may find. While being cautious of BS, of course.

Excellent, and yes -- re. cacti the "BS factor" is everywhere in gardening websites, so if/when you see it, this forum will be a great place for calling it out.

Since I now know that you're growing cacti in the house 24/7/365, here are a few final thoughts...

• Day length influences growth and dormancy. If you can put your grow lights on a timer, you'll be able to emulate day lengths as follows:
  • January -- 10 hours
  • February -- 11 hrs.
  • March -- 12 hrs.
  • April -- 13 hrs.
  • May -- 14 hrs.
  • June and July -- 15 hrs.
  • August -- 14 hrs.
  • September -- 12 hrs.
  • October -- 11 hrs.
  • November -- 10 hrs.
  • December -- 9 hrs.
  I'd say that your cacti are actually "semi-dormant" during fall and winter, so misting them every 3 weeks or so wouldn't be a bad idea. Another option -- keep them in a part of the house with overnight lows below 55, in which case you won't need to mist. When the overnight lows are above the low 50s in spring, your cacti will be starting to grow.

• For the growing season, daytime highs in the house should be 72-80. If you set your air conditioner's thermostat to 78 in the summer, you won't need to water any more often than you would in the spring.

• Stagnant air in the house leads to all kinds of problems for cacti and succulents. If that's the case in your house, a fan near your plant table will keep the air flowing -- all you need is an artificial "breeze" and nothing more during the day. (Not sure if you would need it at night, though.)

There's only one way to water cacti in the growing season -- deeply, as in water coming out of your pots' drain holes. However, saucers under the pots trap water that should've drained out, producing the "wet feet" problem you need to avoid. Water your pots over the kitchen sink and wait until the water stops dripping out, then move your cacti back over to your plant table. How often should you water? If you wouldn't mind taking a somewhat scientific approach to determine your watering schedule, do this:

• Buy a digital kitchen scale if you don't already have one.

• Weigh each pot while the mix is bone dry, and write down the weight.

• Saturate the mix with deep watering, weight each pot again, and write down the weight.

• Weigh the pots on a daily basis until they're back to their dry weights. Make a note of how many days it took for the pots to go from wet to bone-dry.

Wet-to-dry times are a function of pot volume, so chances are that you'll have different times for different cacti. Quite frankly, they won't mind if their roots are bone dry for a week or so, and unfortunately beginning growers end up killing their cacti with kindness because they water too often. Bear that in mind as you figure out a watering schedule that'll work for all of your cacti in the spring/summer growing season.

Steve, I can't thank you enough for all your help

My pleasure! If you have any further questions, please don't hesitate to ask.

[hoopgod32]

Okay, this'll be a good discussion for you...

Cacti and succulents aren't sensitive to fertilizers in general, but they are sensitive to the wrong ones. I'll explain what we mean by that:

• The "Big Three" major nutrients are nitrogen (N), phosphorus (P), and potassium (K).

• Fert manufacturers in the US report P as P2O5 and K as K2O (that is what you'll see in the label's guaranteed analysis). While the oxygen in P2O5 and K2O supports the plant's overall health, it has no nutrient value, so all we're concerned about are the actual amounts of P and K going to the plant. %P2O5 x 0.436 = %P, and %K2O x 0.83 = %K.

• The ratio of N, P, and K tells us if a fert is well-balanced or not. Contrary to what you may have heard or read elsewhere (and I fell for this before Mike educated me on the matter) -- if a fert's N, P, and K numbers are the same (5-5-5 and 7-7-7, for example), it is not well-balanced. The basic "rule of thumb" -- P lower than N, K higher than both.

With NPK ratios, N is always a constant of 1, so the variables are P with an acceptable range of 0.25-0.35, and K with an acceptable range of 1.1-1.7. P is the biggest problem when it's too high because anything above 0.35 per feeding will eventually inhibit root growth, stem growth, and flowering over time. When you look into different fertilizers, you can easily calculate their ratios by doing this:

• %P/%N = the number for the P side of the ratio.

• %K/%N = the number for the K side of the ratio.

The General Hydroponics FloraMicro and FloraBloom give me a combined NPK number of 5-5-5. Now we'll go through the math. 5% P2O5 x .436 = 2.18% P and 5% K2O x .83 = 4.15% K, so the true NPK number is 5-2.18-4.15. Next, turn it into a ratio -- 2.18% P/5% N = 0.44 on the P side of the ratio. Too high. 4.15% K/5% N = 0.83 on the K side of the ratio. Too low. I corrected the imbalance by adding the right amounts of ammonium sulfate and potassium sulfate.

Really great thread Steve! What do you think about Megacrop? NPK of their current batch is 10-7-18 which is 10-3-15 after elemental conversions. Comes out to 1-0.3-1.5 which is right in line with the acceptable ranges you noted. The hard water in AZ should make for close to 3 or 4:1 Ca to Mg as well as 1:1 N:Ca. Packed with other beneficial stuff like chelated micros, silica, seaweed, amino acids (like Recharge), etc.

[Steve Johnson]

What do you think about Megacrop? NPK of their current batch is 10-7-18 which is 10-3-15 after elemental conversions. Comes out to 1-0.3-1.5 which is right in line with the acceptable ranges you noted. The hard water in AZ should make for close to 3 or 4:1 Ca to Mg as well as 1:1 N:Ca. Packed with other beneficial stuff like chelated micros, silica, seaweed, amino acids (like Recharge), etc.

Went onto the Mega Crop website -- I didn't see 10-7-18, so let's investigate their 9-7-14:

Mega_Crop_guaranteed-high-res.png (138.48 KiB) Viewed 93 times

It looked good at first glance, but I see a couple of problems. First, the nitrogen is almost entirely Nitrate N -- fine for growing crops hydroponically, but cacti need to have a certain amount of Ammonium N, and what we have here doesn't cut it. Second, cacti are genetically adapted to living on "thin soup", and IMO the seaweed and amino acids won't do anything for the plants.

The difference between Nitrate N and Ammonium N requires an explanation, so these quotes from trace&save (http://traceandsave.com/the-fate-of-nit ... mmonium-n/) should be instructive:

• "Nitrate nitrogen is a lavish element. It requires a lot of energy from the plant (carbohydrates) in order for it to be absorbed. Its transport system in the plant is the most expensive; it requires 4 times the amount of energy to move around the plant than other forms of nitrogen. Yes, it does the job, you will get big growth response.
  
  "However, although the plant will grow faster you have to be prepared to sacrifice carbon in the process. Carbohydrates (energy) produced through photosynthesis need to be moved from the leaves to the roots, where they are stored and used later during the regrowth or flowering of the plant. If those carbohydrates are hijacked and used to maintain the lavish lifestyle of nitrates, your plant root growth will be limited." [Note: The growth response won't be all that big in desert cacti, but too much nitrate N at the expense of their optimal root growth will be a problem for them over the long run.]

• "When it comes to the uptake of ammonium nitrogen, the plant absorbs it with a lot less energy. Unlike nitrate which requires four energy carriers, it requires just one. When nitrate nitrogen arrives at its location in the plant it needs to be converted back into ammonium first before it is digested, whereas ammonium doesn’t require this process since it is already in the correct form. The one disadvantage with ammonium is that it can be toxic to the plant if it is absorbed in high quantities.

As a general rule, I aim for a Nitrate-Ammonium ratio of about 2-1, and IMO this tallies well with what we see in the quotes. Sorry, but I can't recommend the Mega Grow fertilizer for cacti.

[hoopgod32]

Thanks so much for your input! The 10-7-18 is a bit buried and referenced in their FAQ. Evidently it can change batch-to-batch; they should update the picture.

I agree the "additional" ingredients may be a bit overkill, but I do know lots of cacti growers have had great results incorporating seaweed/kelp and Recharge (a popular innoculent) includes amino acids in their mix for a reason. Are you sure nitrate should be 2:1? I don't think that's accurate. I've seen a ton of cacti growers recommend Masterblend and it contains mostly Nitrate Nitrogen (no more than 15% ammonium). GeeBee even recommends a 80/20 ratio. A good description pulled from Reddit:

From here: "Ammonium, the positive ionic form of nitrogen, has to compete with calcium, magnesium, potassium, and most micronutrients since they are all uptaken in equivalent quantities relative to the presence in the soil. Nitrate, however, is a negative ion and only really competes with phosphorus and sulfur. It's been demonstrated across a wide variety of plants that they preferentially uptake nitrate over ammonium. When it comes to soil in the ground that has a rich and stable microbiome nitrifying bacteria are present and high enough quantities that even though pretty much all of the nitrogen going into the soil is going in as ammonium, usually in the form of organic matter, enough is converted to nitrate to not be a problem for plants. However, in containers, it's harder for nitrifying bacteria to survive and it's best to do a little bit of the work for them and just feed directly with nitrate."

From here: "This leads to the second point, nitrogen in deserts in usually in the form of nitrate. Nitrate is very stable and the little water in deserts means it doesn't get washed away very easily. Nitrate is the form of nitrogen most cacti would have ev0lved to use and many cacti probably don't have the means to effectively use nitrogen as ammonium (with the probable exception of tropical and wet-climate cacti like Rhipsalis)."

[Steve Johnson]

Are you sure nitrate should be 2:1? I don't think that's accurate. I've seen a ton of cacti growers recommend Masterblend and it contains mostly Nitrate Nitrogen (no more than 15% ammonium). GeeBee even recommends a 80/20 ratio. A good description pulled from Reddit:

From here: "Ammonium, the positive ionic form of nitrogen, has to compete with calcium, magnesium, potassium, and most micronutrients since they are all uptaken in equivalent quantities relative to the presence in the soil. Nitrate, however, is a negative ion and only really competes with phosphorus and sulfur. It's been demonstrated across a wide variety of plants that they preferentially uptake nitrate over ammonium. When it comes to soil in the ground that has a rich and stable microbiome nitrifying bacteria are present and high enough quantities that even though pretty much all of the nitrogen going into the soil is going in as ammonium, usually in the form of organic matter, enough is converted to nitrate to not be a problem for plants. However, in containers, it's harder for nitrifying bacteria to survive and it's best to do a little bit of the work for them and just feed directly with nitrate."

From here: "This leads to the second point, nitrogen in deserts in usually in the form of nitrate. Nitrate is very stable and the little water in deserts means it doesn't get washed away very easily. Nitrate is the form of nitrogen most cacti would have ev0lved to use and many cacti probably don't have the means to effectively use nitrogen as ammonium (with the probable exception of tropical and wet-climate cacti like Rhipsalis)."

The subreddit in your first link is specific to discussions of Trichocereus. From Durtndur (whoever that is) -- "Aim for an 80/20 ratio of nitrate nitrogen to ammoniacal nitrogen. Trichocereus love a heavy feed compared to other cacti". If the 80/20 ratio works for Trichocereus, that's fine, but I wouldn't make any assumptions about applying it to most or all other desert genera.

Kyletsenior's post in the Reddit Cactus Corner appears to hold more weight because he was an analyst working for a fertilizer manufacturer. But as he said right up front, "I'm certainly no expert in cacti." On the other hand, we do have an expert on the forum, MikeInOz -- professional horticulturalist with a deep knowledge of cacti. Mike uses a slow-release Cactus & Succulent fertilizer made by Osmocote, and this is the fert's chemical analysis:

Osmocote_c&s_formulation.JPG (96.71 KiB) Viewed 48 times

(Unfortunately the Osmocote is sold only in Australia and New Zealand.) You'll note that the ammonium-nitrate ratio is roughly 1-1. What about the urea component? From "The Cal-Mag of my dreams?" thread:

Urea is converted to ammonium either in the soil by bacteria or in the plant using the enzyme urease. (they have recently discovered nickel is needed for that process but you can basically think of urea as ammonium because it is converted so quickly in the mix.)

Same thread, and this is Mike's experience with the Osmocote:

My cacti get double the ammonium/urea N than Nitrate N. They are growing extremely well. Quite fast but still compact and with good spination. Mammillaria bertoltdii, leuthyi and hermosana have all flowered in their second year. Ariocarpus seedlings also growing fast (for arios). That's the kind of result I'm looking for! They obviously like the ammonium. I would be reluctant to change without a good reason.

There we have it -- contrary to what kyletsenior believes, desert cacti are perfectly capable of using N from ammonium.

Potting medium is an important part of the equation, and this is Mike's approach:

For fertilizer, I use Osmocote for cacti and succulents with an K/N ratio of of about 1.3. I use gypsum of all cacti as a top dressing for Ca. For the limestone species I add washed limestone/dolomite ''sand'' trickled down into the dry mix after potting up to supply more Ca and Mg. There is also Mg and a little Ca in the osmocote and all trace elements as well. For more trace elements I use home made compost and/or 2 year old cow manure at about 10-20% depending on the species. (desert or forest/grassland habitat)

I'd consider this to be a soil-based mix -- for cacti being grown under cultivation with such a mix, a nitrate-ammonium ratio of 1-1 sounds about right. I'm growing 64 of my 68 cacti with a pure pumice and granite gravel mix (essentially a hydroponic mix), so that 1-1 ratio would lead to problems with ammonium toxicity. Based on my 13 years of sound growing experience, I found that a nitrate-ammonium ratio of 2-1 is correct for a pure mineral mix, although I think it should be fine for soil-based mixes too. There's no getting around the fact that nitrate and ammonium have 2 different functions in cactus growth:

• Nitrate pathways send N mostly to the stem.

• Ammonium pathways send N mostly to the roots.

If I had been using something like Masterblend for the last 13 years, my cacti wouldn't be doing so well. The trick is to have the right balance of nitrate and ammonium, and this is determined by the type of mix the grower is using. By the way, you'll get better advice here than you would on on social media platforms like reddit.

[MikeInOz]

From [url=https://www.reddit.com/r/sanpedrocactus ... s/119f5ju/ However, in containers, it's harder for nitrifying bacteria to survive and it's best to do a little bit of the work for them and just feed directly with nitrate."

That is incorrect. Nitrifying bacteria are perfectly able to survive and thrive in any potting mix so long as it is no lower than about pH6 and the mix reasonably warm. NH4 is converted to NO3 in a matter of weeks.
In fact the acidification of mixes in nurseries is suspected of being mainly due to the conversion of applied ammonium to nitrate and the subsequent leaching of that nitrate as it takes Ca (mainly) with it. So all we need to do make sure there is a constant supply of Ca to replace it.
I have no idea of the final mix of NH4 to NO3 the plant takes up when given mainly NH4 but I have found no problems at all feeding mainly ammonium or urea - as long as the potential acidification is understood.

Nitrate is the form of nitrogen most cacti would have ev0lved to use and many cacti probably don't have the means to effectively use nitrogen as ammonium (with the probable exception of tropical and wet-climate cacti like Rhipsalis)."

DISTRIBUTION OF DIFFERENT FORMS OF NITROGEN IN SOME DESERT SOILS
NISHITA, H.; HAUG, R. M.
Author Information
Soil Science 116(1):p 51-58, July 1973.
BUY
Abstract
The distribution of different forms of N in desert soils collected at Nevada Test Site were examined. Soil profiles were sampled in 7.6-cm increments to various depths of which the maximum was 91.4 cm. Among the soil profiles examined, the different forms of N in the surface layer (0.0–7.6 cm) was always NO2-N (not detectable) < extract-able NH4,-N < NO3-N < fixed NH4 +-N < organic N. In the sublayers, some variations from this order of N forms occurred in that the extractable NH4-N was greater than NO3 -N with the presence of trace amount of NO2-N and/or the fixed NH4-N was greater than organic N.

[hoopgod32]

Thanks so much for the input and great information! So moral of the story is majority nitrate nitrogen is bad...dang. Thought I'd found a really great all-in-one water soluble solution. I agree - Reddit is full of noise whereas there's way more value here.

Mike - do you exclusively use Osmocote's cacti fertilizer with a few other top dressings to supplement Ca/Mg? Do you know of any all-in-one water soluble solutions available in the US that are decent alternatives? I have hard water here in AZ, so Ca/Mg ingredients aren't as much of a concern.