Good start! To get the most for my buck, I buy a straight 20-20-20 and dilute it to 10% strength. I also add small amounts of ammonium sulfate, Superthrive and vinegar.

To save myself trouble, I figured out how to mix a super-strong (20X) solution in a spray bottle that works out to be a 10% dilution if I use 4 squirts of the stuff in a 1.5 liter misting jug. It took me about an hour to do the math but I wrote it all down and now all I do is squirt and go. The liquid in my concentrate is about 50% vinegar, 5% superthrive, 45% water. You can start using a diluted fertilizer right away with Agave (most) seedlings and pretty much continuously until next winter.

Thank you hanzrobo for the very helpful tips! I am using distilled water at neutral pH right now--what pH level do you suggest for Agave?

Hoovb,
But I would start with some thing very weak and natural like a compost tea or Alfalfa pills for people mixed in there water. When they are bigger I would go to chemical and weak like Hanzrobo said. I messed up once and burned my young plants so I am afraid of chemicals.

Start fertilizing when first true leaves are apparent. Plants don't USE nutrients in a 1:1:1 ratio, so why supply them in that ratio? Plants use about 6X as much N as P, and about 3/5 as much K as N. When you do the calculations that take into consideration that P is reported (expressed) as P2O5 and K as K2O, you'll find that fertilizers with a 3:1:2 RATIO supply nutrients in almost exactly the ratio at which plants use them. Examples of 3:1:2 ratio fertilizers are 24-8-16, 12-4-8, 9-3-6) I prefer Foliage-Pro 9-3-6 because it's a 3:1:2 ratio, it has ALL the nutrients essential to normal growth (few fertilizers do), it's soluble, and it derives most of its N from nitrate sources - no urea). BTW - there is a considerable advantage in supplying nutrients in the right ratio - it allows the lowest possible o/a fertility level (EC/TDS) without deficiencies occurring.

The strength of your solution depends almost entirely on your watering habits and intervals between applications. Plants make their own food, but if fertilizer actually WAS plant food, we could say that a plant's diet consists entirely of salts - no matter whether they come from a bottle of Miracle-Gro, compost, or a dead fish. There is also no scientific evidence that new roots on young plants are any more susceptible to plasmolysis (fertilizer burn) than new roots on old plants, so you can fertilize at recommended rates as long as you're regularly flushing the soil when you water (to prevent excessive build-up). If you CAN'T flush the soil w/o having to worry about it remaining wet too long A) your soil is inappropriate B) the soil will hamper implementation of a reliable supplementation program, so you'll need to figure out a way to work around it (the poor soil).

The hobby growing community has mixed feelings about Superthrive. The scientific community doesn't. Use it if it makes you feel better, but don't expect its effects on your plant material to be anything you can actually quantify (unless you overuse - THEN it will let you know you messed up - the synthetic auxin it contains is one of the same ingredients (defoliant) in the infamous Agent Orange.

Click the embedded link to see what Linda Chalker-Scott, PhD has to say about Superthrive. I wrote an article about Superthrive well before Dr Scott offered her opinion. Those things the articles note parallel each other very closely.

Al

Speaking of Salt...

Long and hard the North winds blow,
and carry on to Idaho,
where all the Idahoans know,
exactly how potatoes grow.

Plants in winter, plants in fall,
know a plant, you know them all,
Plants are plants and plants, they say,
behave the same in every case.

Books are written, books are read.
Plants are grown until they're dead.
All the words relayed in stride,
are only useful when applied.

Old beliefs are like a pair of old shoes - we value their comfort so much we ignore the fact they're full of holes. Almost every man prefers the comfort of belief to the exercise of judgment because believing is easier than thinking; which brings us full circle to why there are so many more believers than thinkers.

Al

Well said, but it is possible to think while flying, seat of pants and all. Many habits/behaviors of plants remain a mystery to even the most educated of growers. There are many styles of growing and many plants to be grown. I'll always choose experience over science, which is not general or absolute. A mixing of solid, proven technique/science, experience and a keen intuition/ability to adapt is what is necessary. As far as beliefs, dogmas, and legends go, well I couldn't ask for better company, let's say that.

Keen observation never hurts.

Thanks all for the helpful and educational comments!

It's true that everything about how plants work/respond is not precisely known, but a very large fraction of the plant sciences are well defined, and what we're talking about (nutrition/ soil science) is well defined. If the goal is establishing a nutritional supplementation program that is as good as it can be, we can easily predict/illustrate you can't get there using 20-20-20 and Superthrive with enough certainty that to withhold agreement would be unreasonable. Experience is most valuable when it's gained as practical application in validating something you've already learned. Trial and error (flying by the seat of your pants) is time consuming and costly. What value in experience if it consists of the continual repetition of inefficiencies?

Hoovb - the ability to be a keen observer is very valuable when it comes to tending plants. Unfortunately, a very high % of us hobby growers are perfectly willing to make up science to fit what we think we are observing, which is why there are so many misconceptions about how plants respond to their environments, not to mention the horticultural myths that have been elevated to the status of being nearly unquestionable.

Best luck with your new responsibilities. ;-)

BTW - I'll offer a description of how I approach fertilizing containerized plants. If you think it's reasonable, you might consider working toward implementation:

The goal for fertilizing containerized plants can easily be described. You should work toward implementation of a program that ensures all the nutrients plants normally secure from the soil are in the soil solution at all times, in the ratio at which the plant actually uses the nutrients, and at a concentration high enough to ensure no deficiencies, yet low enough to ensure the plant isn't impeded in its ability to take up water and the nutrients dissolved in water. This goal is easily achievable using one water soluble synthetic fertilizer that has all the nutrients in a favorable ratio. You CAN use organic forms of nutrition, like fish/seaweed emulsions or various types of meal, but that makes it much more difficult to achieve the goal.

Al

Well, I do add a touch of ammonium sulfate which ups the N slightly but I don't believe the generalization that all plants prefer a 3:1:2 ratio to be correct. Many slow-growing succulents will bloat even with my 3-2-2, even when interspersed with plain water. I can't speak for the entire plant kingdom, but some generalizations just don't work in the succulent world.

The Superthrive thing is up for debate but I've noticed a significant improvement in seedlings treated with the stuff after transplant, and I'm not the only one. I've transplanted 1000's of seedlings. I haven't checked the pudding but...

Apparently, you've managed to work out some psuedo-hydroponic system for your plants. I just don't agree with it. You gritty mix may work well for a variety of plants and a few succulents but I'm convinced that it's generally wrong for succulents. I hate to do this but I'm tired of seeing people all caught up in the search for ingredients, going to all this effort, only to see their plants(succulents) suffer over the next year. I grow succulents (well). I have a proper mix for them.

You and I are very different sorts. I grow many different succulents, relying on science, education, technique, but overall I rely on my ability to read them in my own environment. I am very experimental, regardless of what I read. I need to see it for myself. My plants are fodder for my learning process; poor them. Life is short. Do you want to compare results? Numbers? I always read your elaborations but never see the proof. I appreciate your contribution, Al, but I think you may need to re-evaluate your one-size-fits-all method.

I use a 3-1-2 hydroponic fertilizer at 50ppm N every other watering for agave at that stage. Mine are always in straight pumice at that point so the hydroponic solution provides immediately avalable N.

Let's start here. This is my idea of the ideal way to fertilize - noted above. Can you improve on the concept; or would you change it in any way? Be specific.

The goal for fertilizing containerized plants can easily be described. You should work toward implementation of a program that ensures all the nutrients plants normally secure from the soil are in the soil solution at all times, in the ratio at which the plant actually uses the nutrients, and at a concentration high enough to ensure no deficiencies, yet low enough to ensure the plant isn't impeded in its ability to take up water and the nutrients dissolved in water.

Al

Nailed it.

Ok - we agree on the concept. So how can it be implemented using a 1:1:1 ratio fertilizer? We know that as plants grow, they use roughly 6X as much N as P, but all we need to agree on is that plants don't use nutrients in even close to a 1:1:1 ratio to see that reaching the goal is impossible in both theory and practical application using 20-20-20.

Al