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Considering fertilizers

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Considering fertilizers

Postby Steve Johnson » Sun Feb 19, 2012 5:37 am

I haven't been able to spend much time visiting face-to-face with people experienced in cactus cultivation. In fact, I didn't think seriously about different fertilizers until I joined the CactiForum in November, so I decided to try my luck with any research I might find there. It has been a challenge since a number of discussions on cactus fertilizers often miss crucial details that need better info. However, given enough persistence I'm learning how to spot the people who seem to really know their stuff, and those who are kind enough to share solid experience with us. My starting point came with a recommendation from Darryl at CoronaCactus nursery for using the Dyna-Gro 7-7-7 fertilizer. Here's the specs:
Dyna-Gro_7-7-7_specs.jpg
Dyna-Gro_7-7-7_specs.jpg (33.14 KiB) Viewed 599 times

iann wrote:That fertiliser looks fine to me. Is the 98ppm total dissolved solids, or 98ppm of each main nutrient? If 98ppm of each you could even go more dilute with every watering.

Nitrogen in soluble fertilisers basically comes in three forms: nitrate; ammonium; and urea. Nitrate is half of a salt and always comes with something else, sometimes another major nutrient and sometimes even ammonium. If you don't want to read further, you could just go with the simple rule that a mix of forms will cover most eventualities. I looked on my Chempak labels and noted that basically the 12.5-25-25 and 20-20-20 have about the same amount of nitrate and ammonium (and some urea), with the extra nitrogen in the 20-20-20 mainly coming from urea.

Nitrate ions are highly soluble and mobile in soil so they are subject to leaching, so you should consider any nitrate form nitrogen to be gone by the next time you water. Nitrates are taken up rapidly by roots, are highly mobile inside the plant, and can be utilised very quickly. This means you get a very rapid greening effect from nitrate fertilisers, but an excess can quickly lead to weak over-lush growth.

Ammonium is usually applied as half of a salt, or occasionally as the gas ammonia but not in a packet of soluble fertiliser. Ammonium ions are more tightly bound to soil particles so they can last longer between waterings, but are still short-lived compared to other nutrients. Ammonium is readily taken up by roots but must be converted by the plant before it can be used so it acts slightly slower than nitrate, on a timescale of days rather than hours. Plants differ in their preference for nitrate or ammonium ions, but the vast majority will take either. Ammonium-based fertilisers tend to have the most acidifying effect in soil, and nitrates the least. The worst situation is when ammonium ions are converted to nitrates, which is the acidifying process, and then the nitrates leach out of the soil.

Urea acts even more slowly than other forms of nitrogen fertiliser, but is relatively persistent in soil. It is either converted by soil bacteria into ammonium, or taken up quite slowly by the roots. Urea is popular for high nitrogen applications because of the persistence, low danger of burning, the highest nitrogen content of any fertiliser (except anhydrous ammonia which is a highly toxic gas), and ease of use on bulk scales. It is less popular in soluble fertilisers for basically the same reasons, but is often the basis of slow-release fertilisers.

Ian's discussion on the 3 Nitrogen sources for cacti came as a totally new experience to me today, so I'll bring this into the mix as I examine the issues here.

Per Darryl's advice, the dilution with Dyna-Gro 7-7-7 is 1 teaspoon per gallon of water. He did the math, and it works out to 98 ppm for the total ingredients in that fertilizer. According to his experience, the dilute fertilizer-water solution is used to water cacti every time during the growing season. I'll have to determine watering frequency by temperature conditions, although at the height of summer I believe it'll be once a week with good drenchings as appropriate by species requirements. My part of L.A. is close enough to the coast that any heat waves won't be as long or as frequent compared to the more inland areas. Also, with the exception of a few plants, my cacti will be going over to a decomposed granite/pumice mix when I'm ready for the new growing season.

EDIT -- I need to correct this. The formula for ppm is 7/100/768 x 1000000 = 91. That works out to 91 ppm for total N, 91 ppm for P, and 91 ppm for K. If I dilute the Dyna-Gro 7-7-7 at a rate of 3/4 tsp. per gallon of water, the ppm for NPK will be 68, 68, and 68.

I have two options I need to think about re. pros and cons. The first option is the Dyna-Gro 7-7-7. On the pro side, Ian confirms that Darryl's choice is a good one. However, thanks to Ian's understanding about the importance of a nitrate-ammonium-urea balance, I'm concerned if the lack of urea in Dyna-Gro could become a long-term problem as he describes. This is where it would help me to know if the ammoniacal and nitrate combination with Dyna-Gro overcomes this problem by fertilizing less frequently, or it's not even a problem at all for cacti.

My other option would be to find a liquid fertilizer with a nitrate-ammonium-urea mix. All I can seem to find are either nitrate- or urea-based fertilizers. However, to be honest the only fertilizer I use is urea-based, and it's the controlled-release fertilizer I purchased from the California Cactus Center when I started my new collection last June. Trying to insert fertilizer pellets down through the gravel top dressing of my cacti thrills me not at all, so it'll have to be a liquid fertilizer for me. The CCC does have one, and I'll ask them if their liquid uses a nitrate-ammonium-urea mix. If they do, I'll get the specs and run them past our forum members (Ian especially!) to see if it's the right stuff. If not, hopefully someone here can recommend something good we can find here in the U.S. (I'm pleased to say that when it comes to the "urea free" cult, you can include me out. I'm not interested in fads, so I only care about results if they're backed up with some reliable science.)

Many thanks to Darryl and Ian for helping me out here. I really do appreciate the information resource we have on the forum, and I wish we had the Internet about 40 years ago!

Steve
Last edited by Steve Johnson on Sat Apr 21, 2012 5:13 am, edited 3 times in total.
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Re: Considering fertilizers

Postby iann » Sun Feb 19, 2012 1:11 pm

I wouldn't worry about a lack of Urea. I wouldn't even panic if the nitrogen was entirely from a single source. You've got a mix of nitrate and ammonium, it will be fine.

7% @ 1 teaspoon per gallon = 7 / 100 / 768 = 91 / 1000000 = 91ppm. Like I said I'd go a little less than this with every watering but I don't think you'll see problems any time soon. I tend to go a little less than this, plus I don't bother every single time I water. Just like water, it is hard to apply too little but easy to apply too much.

Persistent mild overfertilising over a period of years can cause problems, but details depend on how fast the plants grow, your soil, watering practices, etc. The sort of symptoms you might expect is that the plants appear to grow well and then stall out. They appear to become over-saturated with salts and start to have difficulty taking up water. Some of the problem could be in the soil, a problem traditionally referred to as salt buildup (although that sometimes describes the slightly different deposition of calcium carbonate from hard water). Salt buildup of either kind is made worse with high evaporation rates from a a hot arid climate or from porous clay pots. The traditional solution has been occasional flushing through with pure water.
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Re: Considering fertilizers

Postby Steve Johnson » Mon Feb 20, 2012 12:00 am

iann wrote:I wouldn't worry about a lack of Urea. I wouldn't even panic if the nitrogen was entirely from a single source. You've got a mix of nitrate and ammonium, it will be fine.

7% @ 1 teaspoon per gallon = 7 / 100 / 768 = 91 / 1000000 = 91ppm. Like I said I'd go a little less than this with every watering but I don't think you'll see problems any time soon. I tend to go a little less than this, plus I don't bother every single time I water. Just like water, it is hard to apply too little but easy to apply too much.

Persistent mild overfertilising over a period of years can cause problems, but details depend on how fast the plants grow, your soil, watering practices, etc. The sort of symptoms you might expect is that the plants appear to grow well and then stall out. They appear to become over-saturated with salts and start to have difficulty taking up water. Some of the problem could be in the soil, a problem traditionally referred to as salt buildup (although that sometimes describes the slightly different deposition of calcium carbonate from hard water). Salt buildup of either kind is made worse with high evaporation rates from a a hot arid climate or from porous clay pots. The traditional solution has been occasional flushing through with pure water.

Very good, and it looks like the Dyna-Gro 7-7-7 will be a winner. Yes, indeed better too little than too much, and it avoids a common pitfall by inexperience with cacti.

Since you would recommend going a little less on the Dyna-Gro, I'm wondering if diluting with 3/4 teaspoon (I believe that's 68 ppm) is sufficient. (I try not to get too hung up on constantly being precise, but it's a long-standing tendency of mine.) Also, I remember from years ago that occasional flushing with distilled water does wonders to remove salt buildup. I suspect that would be the white residue I see on the outsides of my terra cotta pots. When the weather is warm enough (I think probably June), it'll be time for a good drench.

Thanks, Ian!
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Re: Considering fertilizers

Postby A. Dean Stock » Tue Feb 21, 2012 5:36 am

The Dyna Grow 777 will do an excellent job for you on cactus. I used it for many years on orchids with very good results. I'd still be using it except for the fact that if one requires large quantities of it the shipping is prohibitive compared to dry fertilizers. You will not miss the Urea at all.
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Re: Considering fertilizers

Postby Succulent » Wed Feb 22, 2012 3:04 am

I like the full set of micronutrients, Ca and S in the Dynagro 777. I would prefer less nitrogen though.

Does anyone know of a similar fertilizer with less nitrogen?

Dean-Which dry form do you use?
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Re: Considering fertilizers

Postby A. Dean Stock » Wed Feb 22, 2012 4:55 am

I use the MSU fert. for "pure" water as I mix it in R/O water. At times I have used a fert. based on the MSU formula sold by Roberts Flower Supply. All of my cacti are outdoors and I only fert. in the spring as good growth starts.
They don't seem to require much in the way of fertilizer when in ground but it helps a lot in the early spring.
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Re: Considering fertilizers

Postby new_age » Wed Feb 22, 2012 12:38 pm

For cacti I suggest two fertilizers:

1) Scotts Universol Basis: high level K and P
http://www.scottsprofessional.com/en/un ... basis.html
2) Chempak Cactus and Succulent fertilizer: high level K and P
http://www.amazon.co.uk/Chempak-Cactus- ... B004KQ4AF6

and a little reading:
http://www.succulent-plant.com/fertiliser.html

The general idea with cacti fertilizer is a low level N part.
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Re: Considering fertilizers

Postby Steve Johnson » Wed Feb 22, 2012 6:38 pm

new_age wrote:For cacti I suggest two fertilizers:

1) Scotts Universol Basis: high level K and P
http://www.scottsprofessional.com/en/un ... basis.html
2) Chempak Cactus and Succulent fertilizer: high level K and P
http://www.amazon.co.uk/Chempak-Cactus- ... B004KQ4AF6

and a little reading:
http://www.succulent-plant.com/fertiliser.html

The general idea with cacti fertilizer is a low level N part.

The fertilizer page you linked to is interesting, but it seems to miss a crucial piece of information -- parts per million (ppm). That tells us the amount of dilution in water, which is required to know how much of the nutrients are being delivered to cacti. Basically it's a dose-response relationship, but without knowing dilution rates, how can we know if we're fertilizing enough, not enough, or too much? (I'll take Ian's cue and say once again that not enough is better than too much!)

When I began delving into fertilizers on the Cultivation forum, I must admit that hearing about the NPK of various ferts didn't give me enough info to be useful. However, when I saw Ian talking about dilution rates and ppm, he finally gave me some context on the whole thing. Please bear in mind that I have decided to go with a dilute fertilizer/water solution for my cacti, replacing it in favor of the controlled-release fert I started using last June. As a matter of general interest, we should look at these factors in combination: NPK, Nitrogen source(s), trace nutrients, and total fertilizer dilution in ppm. I selected the Dyna-Gro 7-7-7, and because I'm trying to educate myself on cactus cultivation as much as I can, I wanted to consult people with sound experience and a good track record for success. Darryl, Ian, and Dean have been incredibly helpful, so I feel that I've been pointed in exactly the right direction here. Of course there will be a number of different opinions, so for those who are looking at other ferts, hopefully I'm doing a small part in bringing up all the factors that must be considered.
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Re: Considering fertilizers

Postby iann » Wed Feb 22, 2012 8:16 pm

It says right on the package: 1-5-9. That's 10,000-50,000-90,000 in ppm. Dilute to the level you want.
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Re: Considering fertilizers

Postby Succulent » Wed Feb 22, 2012 9:21 pm

new_age wrote:For cacti I suggest two fertilizers:

1) Scotts Universol Basis: high level K and P
http://www.scottsprofessional.com/en/un ... basis.html
2) Chempak Cactus and Succulent fertilizer: high level K and P
http://www.amazon.co.uk/Chempak-Cactus- ... B004KQ4AF6

Seems like neither is available in the US, although Scotts should be.

Anybody know of similar US products?
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