I've been following the work of Elton Roberts since I first found out about him through the Cultivation forum last December. That introduction was quite revealing when I discovered his CSSJ article on cacti and alkalinity. Then recently I started hearing about Elton's fertilizer regimen, and I emailed him to ask for some more in-depth information. He was kind enough to oblige my request, and it turns out that's where the real discovery was. This has completely changed my approach to fertilizing cacti and succulents, and I'd like to pass along what I've been finding for anyone who may get some use out of it. Before I continue, I should mention that when all plants are watered using hard water, they will suffer the effects sooner or later. By neutralizing the Calcium bicarbonate in hard water through acidification, plants are able to absorb the moisture and nutrients they need through their roots. I'll discuss fertilizers before we look at acidification, but you should know that the two need to go hand-in-hand. If you don't address the pH in your water, then all the fertilizer in the world won't do any good for your c&s.Fertilizers
I've been reading and re-reading Elton's article Ammonium Nitrogen and Acidic Water for Xerophytic Plant Growth
from the July 2010 issue of the Cactus and Succulent Journal
, and it becomes increasingly apparent that all three sources of Nitrogen are not
equal when it comes to maintaining optimum health for c&s over the long term. I have two versions of his article for you here. The first one includes photos showing examples of some cacti before and after using fertilizer supplemented with Ammonium sulfate:https://skydrive.live.com/redir?resid=7 ... LN3d5AsTqk
If you find the column format to be kind of a pain, here's a version in standard paragraph format:https://skydrive.live.com/redir?resid=7 ... vvPEB_GYj8
I highly recommend that you read Elton's article in more detail for yourself, but I can give you a "Cliff Notes" summary to guide you through the rest of this section. For starters, please note that Ammonium Nitrogen packs a lot more nutrient value than either Nitrate or Urea for c&s. Now here's the problem -- Ammoniacal N comprises only part of the total N in ferts. Since the "big three" major nutrients are N, Phosphorus (P), and Potassium (K), you'll need to supplement your fert with Ammonium sulfate to achieve the proper NPK balance.
There are two things we need to be aware of. First, when c&s are kept in pots, they'll need a steady nutrient supply. Therefore it's better to use low fert levels with each watering, instead of "juicing up" the plants once in awhile as they get nutrient-deprived the rest of the time. Second, the amount of Ammonium N depends on the potting medium. Since humus removes N from the soil, a high-humus mix will require more Ammonium N than a mix with little or no humus. I'm using a pumice/decomposed granite mix myself, so there's not even a hint of humus in it. Since I don't have any experience with a mix that uses humus, I'll have to try and extrapolate from Elton's article for you the best I can.
Okay, we're really getting into it now, aren't we? If you don't mind doing some math, you'll find that learning how to speak in parts-per-million will really help you to determine the amount of NPK being delivered to your c&s through regular watering. (If you're math-challenged, you can skip down to the end of this section, and I'll give you a simple recommendation.) Let's begin with Elton's regimen for high-humus soils. His fert is Plantex 20-20-20 diluted at 4 tbsp. supplemented with 8 tbsp. of Ammonium sulfate per 30 gallons of water. When I run the numbers, we see that the Plantex has 100 ppm each for N, P, and K. However, only 20 ppm is Ammonium N, and in a high-humus soil it might as well not even be there. (The plants are still getting their P and K, though.) When we supplement the Plantex with Ammonium sulfate, we'll get 219 ppm of that for a total of 239 ppm Ammonium N. What we're doing is basically a combination of two different ferts to get our c&s the major nutrients they need. The same goes with mineral soils, although we need a different set of numbers here. For a mineral mix, the dilution rate will be 2 tbsp. Plantex and 2 tbsp. Ammonium sulfate per 30 gallons of water. That gives us 52 ppm each of NPK from the Plantex, although only 10 ppm will come as Ammonium N. The Ammonium sulfate makes up 55 ppm, giving us a total of 65 ppm Ammonium N.
The difference between high-humus and mineral soils is both apparent and rather dramatic in terms of their impact on nutrient delivery. With that said, Elton's article doesn't provide any guidelines on what would constitute a high-humus mix, although this may have to be left up to the knowledge and experience of the individual grower. For those who are using mixes with only a small amount of humus, it stands to reason that fert dilutions should be adjusted downward toward the lower end of the NPK scale, but how low should it be? Once again this must be up to the grower. What we can say with certainty is that under-fertilizing is preferable to over-fertilizing, especially over the long term.
The ppm values for Ammonium N, P, and K I'm discussing here should be good benchmarks for any fert one would like to use when supplemented with Ammonium sulfate. However, the proper dilution rates need to be calculated. (Knowing the amount of Ammonium N in your fert is essential to determining the amount of Ammonium sulfate required.) If you feel so inclined, I'm showing my work at the end of this post to give you the basic calculations you'll need. That work also includes calculations for the Dyna-Gro All Pro 7-7-7 and Ammonium sulfate I'm using in my pumice/DG mix. Last year I gave my cacti a controlled-release fert which I now know was pretty much useless, so I'm having to make up for lost time as they're coming out of their nutrient deficiency. To avoid the risk of over-fertilizing, I'll cut my Dyna-Gro and Ammonium sulfate by half, which in turn will bring the ppm values pretty much in line with what Elton recommends for mineral soils. This is a good example of how adjustments can be made when observant growers use some common sense.
I know math exercises may not be something you'd want to deal with, so if you follow the fert "recipes" in Elton's article, that'll give you the right dilutions for whatever mix you're using.Acidification
As I briefly mentioned earlier, Calcium bicarbonate in tap/well water slowly robs plants of their ability to take up moisture and nutrients through the roots. This is precisely why acidification is necessary in order for plants to thrive when your only source comes from hard water. Vinegar and citric acid are both very safe for home use, although not the most practical or cost-effective for large collections and nurseries. In those cases, Sulfuric and Phosphoric acids are better, although they must be treated very carefully, and should not be used until you know how to properly handle them. I'll direct you to Elton's article on cacti and alkalinity for more information here:https://skydrive.live.com/redir?resid=7 ... -G0e6vkGPU
Based on advice from expert growers, we know that a pH of 5.0 - 5.5 is optimal for the health of c&s. Ferts themselves will lower the pH of water, but not enough to do the job. After diluting your fert, you'll need the right amount of acid to bring the pH down into the 5.0 - 5.5 range. Some people try to "guesstimate", but in my opinion it is a poor substitute for knowing the actual pH values in your watering/fert solution. If you can determine those values, the idea is to start with a small amount of acid, check the pH, then continue adding small amounts until you reach the desired final pH. Once you've done this a few times, you should know about how much acid you'll need. However, the pH of the water coming out of your tap can fluctuate, so checking the pH right before each watering is advisable to avoid inadvertently straying from the 5.0 - 5.5 range. If you find that the pH of your watering/fert solution is below 5, throw it away and start again.
Inexpensive colorimetric indicator kits can be found at any hydroponic store, but they tend to be highly inaccurate. I've seen this for myself, and before I started using my water/fert/vinegar regimen on my cacti, I decided to buy a pH meter for the sake of both accuracy and precision. It is understandable for one to feel intimidated by the idea of getting a pH meter, but A. good ones aren't expensive and they're easy to replace when they stop working, and B. pH meters are easy to use if you know how to follow basic instructions. I purchased a Milwaukee Instruments PH600 meter for $21.95 through Amazon, and it has proven to be not only simple, but also rugged and reliable, so I'd definitely recommend it. Here's the link:http://www.amazon.com/gp/product/B005H7 ... os_product
Calibrated meters do need a 7.0 reference solution to maintain accuracy, so you can find that item here:http://www.amazon.com/General-Hydroponi ... y_lg_img_b
Hard water is the primary reason for citing the use of acidification, but it should by no means be the only one. For example, what about distilled water? Since it is supposed to be free of minerals, then it should theoretically have a neutral (7.0) pH. Well, there's a myth I can bust for you -- I recently bought a gallon of distilled water from my local grocery store. I decided to test it with my pH meter, and guess what. The pH was 7.9! How that could be I don't know, but I'd have to acidify it just as much as anything coming out of my tap. (Moral of the story, don't assume anything.) You won't have that with rainwater, since it will be more or less pH-neutral. However, even rainwater with a dilute fert may not give you the desired 5.0 - 5.5 pH range, so you'll probably still need to acidify a little bit. If you're already using rainwater, you may be saying "rainwater + fert = 6.0 pH. That's good enough." Maybe not. Thunderstorm activity fixes Nitrogen through Nitric acid in rainwater. Anyone who has spent time in the desert will know that rain almost invariably comes with thunderstorms. Rain + Nitric acid from lightning = low pH, and the rainwater pH can go as low as about 3.7. (Read Elton's article on cacti and alkalinity, and pay close attention to what he discusses regarding cacti in limestone-rich desert soils. I think you'll find it rather interesting.) In the absence of local thunderstorm activity, acidifying your rainwater/fert solution is useful if it needs to bring the pH down to the 5.0 - 5.5 range.Conclusion
I recently corresponded with John Trager at the Huntington to ask him about his cultivation practices. John has been curator of the Desert Collections for many years, so those who know him (at least by reputation) understand that he is a wizard of a grower. Under the wisdom of "trust, but verify" I asked him about Elton's work, and he backs up what Elton has been telling us. Difficult to argue with this.
I've been incorporating Ammonium sulfate into my watering/fert regimen, although I just started doing it a couple of weeks ago. It's too soon for me to assess the results, but I have the whole summer ahead as I track the progress of my cacti. I'll be keeping my photo archive up to date while things move along, so if those results are good, I'll post before-and-after cactus pics in this thread. Until then, I'll leave you with a little story of what I hope will be a harbinger of good things to come.
Before I started my new collection in earnest last June, I went to my local Armstrong Garden Center just to see what they had in their c&s section. A lot of s, but not much c. (I did buy a Mammillaria spinossissima -- the "red-headed Irishman" has been an old favorite since I was a kid.) I also bought a Sempervivum tectorum ("hen with chicks") which caught my fancy. Then it didn't after I found all the cacti for my collection. I must admit that I neglected the poor thing, and the only water it got was some occasional rain. The Sempervivum was still alive, although barely, and I decided to try it on some of my new Dyna-Gro/Ammonium sulfate regimen. A few days later my "hen with chicks" was thriving
. I could hardly believe it! Sorry I didn't take a "before" photo, but here's what the Sempervivum looks like today:
If I've learned anything from Elton at all, then I'm off to a good start! And if it helps me, I hope it'll help you, too.Fertilizer and Ammonium sulfate calculations
1 gal. = 256 tbsp. 4 tbsp. per 30 gal. = 1 tbsp. per 7.5 gal. 7.5 x 256 = 1920 .2/1920 = .0001 .0001 x 1000000 = 100 ppm ea. NPK
.0385/1920 = .00002 .00002 x 1000000 = 20 ppm Ammonium N
Mineral soil calculations
2 tbsp. per 30 gal. = 1 tbsp. per 15 gal. 15 gal. x 256 = 3840 .2/3840 = .000052 .000052 x 1000000 = 52 ppm ea. NPK
.0385/3840 = .00001 .00001 x 1000000 = 10 ppm Ammonium N
Dyna-Gro All Pro 7-7-7, 1/2 tsp. per gal. for pumice/DG mix
1 gal. = 768 tsp. .07/768 = .000091 .000091 x .5 x 1000000 = 46 ppm ea. NPK
.021/768 = .000027 .000027 x .5 x 1000000 = 14 ppm Ammonium N
Ammonium sulfate 21-0-0
8 tbsp. per 30 gal. = 1 tbsp. per 3.75 gal. 3.75 x 256 = 960 .21/960 = .000219 .000219 x 1000000 = 219 ppm
Mineral soil calculations
2 tbsp. per 30 gal. = 1 tbsp. per 15 gal. 15 x 256 = 3840 .21/3840 = .000055 .000055 x 1000000 = 55 ppm
Pumice/DG calculations, 1/8 tsp. per gal.
.21/768 x .125 = .000034 .000068 x 1000000 = 34 ppm