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.

After investigating a lot of "off the shelf" fertilizers, I have yet to see one that gets the NPK balance right for cacti and succulents. However, there's a lot to be said for the General Hydroponics ferts I'm using, so if you're willing to go through a few extra steps, you'll need the following:

• A digital scale measuring down to .01 grams. Not expensive, and you can find a good one here:
  
  https://www.homesciencetools.com/produc ... g-x-001-g/
  
  Way better than the cheapo scales I found on Amazon.

• Ammonium sulfate and potassium sulfate in powder form. Easily available on Amazon and eBay.

From there I can give you the instructions for making an ammonium sulfate-potassium sulfate stock solution, and a recipe with the right amounts of the General Hydroponics ferts and stock solution going into your watering solution.

I checked out the Fertilome cactus soil, and I think it has fertilizer "baked in". Even if it doesn't, the ingredients (Canadian sphagnum peat moss, horticultural perlite, granite sand, dolomitic limestone, calcitic limestone) were enough to tell me that you'll be better off with the mix I'm recommending.

I've read that succulents can be really sensitive to it.

They are probably less sensitive to dissolved salts than most plants because they come from areas which are not heavily leached by rain. Most of the sensitive plant species come from soils that are always moist or places were there is plenty of rain. Too much nitrogen is usually the main problem.

Mike makes a good point about the high N problem. Dilution = dosage, so what I have in mind will give your cacti the right dosage of N per feeding.

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.