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 26 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'm very surprised as I have seen a ton of growers recommend Masterblend and it contains mostly Nitrate Nitrogen as well. 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)."