You should operate under the premise that virtually all nutrients are lacking & try to figure a way to insure your plants get them. You can take care of the Ca and Mg requirements by adding a tablespoon of dolomitic (garden) lime/gallon to the soil when you make it (most soluble fertilizers will not include these elements). If you use a fertilizer that contains all the minor elements, you won't need an additional micronutrient source for best growth, but if you choose a fertilizer lacking the minor elements, it's best to choose a supplement that will include them.

Probably the best ratio for all but the sweet potatoes would be 3:1:2. If I had to pick something for the sweet potatoes, it would probably be a 2:1:2 ratio, but the 3:1:2 blend will work just fine for all the plants you list. Miracle-Gro makes a fertilizer labeled 'All-Purpose' in either 24-8-16 granular soluble or 12-4-8 liquid, and they will be excellent choices of 3:1:2 ratio fertilizers. They have all the nutrients likely to be deficient in container soils except S (and Ca/Mg as noted above). Another fertilizer that should be EXCELLENT, is Foliage-Pro's 9-3-6 blend. It contains ALL the secondary macros and all the minors. It will be more difficult to find - likely requiring that you order from an online source.

Fertilize often at reduced rates for best results. If your soil drains well, weekly at 1/4 strength is a good rate when plants are growing robustly.

If you have interest in reading more about fertilizers for container plants, follow the link I'll leave below.

Al

Here is a link that might be useful: Fertilizers in Containers

Al, thank you for the reply. It is refreshing to hear some info that is actually based on scientific research- instead of hearsay that is rampant in some of the other forums.

So, I have an "all purpose fertilizer" that probably matches the ratio you specified above-

In terms of the micro nutrients, I will probably not be able to order expensive products online as my disposable gardening funds are a little depleted. Are there natural sources that can provide these (i see some have mentioned seaweed extracts??)? What about adding small ammounts of epsom salts?

Once again, thanks for all of the great info- i can see the subject gets quite complicated and its great that there are some here that are able to explain some of the more techincal concepts in a way that laymen can understand!

Tell me what your fertilizer is and I'll try to answer. It's possible that if you're mixing your own soil and using something like MG with some minors, and liming your soil, that the only element likely deficient might be S.

I'll cover the Epsom salts when I find out what you're using.

Al

Ok, so I'm just trying to get my head around some of these concepts. I see that you say that increasing the phosphorous is not the way to go when fertilizing blooming plants but rather, you want to decrease the nitrogen- therefore, do you switch from 3-1-2 to 2-1-2 (decreasing the N, but keeping the same balance of P and K) when plants begin to blossom????

Miracle Grow 24-8-16 all purpose is what I have.

Plants use about 6 times as much N as P when both are in the soils at adequacy levels. No matter HOW MUCH MORE P you add beyond that, the plant CANNOT use it.

When plants are matured, and all other nutrients are available in adequate amounts, limiting N is going to cause the plant to allocate energy to flowers/fruits. If you limit N, you limit vegetative growth w/o limiting the plants ability to carry on photosynthesis. Since photosynthesis is ongoing - the plant has no where to put energy (not enough N to grow vegetatively - remember?) except into flowers and fruit.

Adding all that extra P unnecessarily raises the EC and TDS of container soils, making it more difficult to absorb water AND nutrients. It can also cause precipitation of both Fe and Mn, causing an antagonistic deficiency of those elements. Since the symptoms of a deficiency of these two elements are chlorotic leaves, you think you need MORE fertilizer and apply MORE P, which only exacerbates the problem.

Overall, plants use very close to a 3:.5:2 ratio of the major macros. Even a 3:1:2 has twice the P a plant will use. Greenhouse operations employ the N limiting trick to bring you compact bedding plants that are already in bloom by fertilizing close to a 2:1:2 ratio to achieve what I described above.

I also mentioned that you can still use a 3:1:2 ratio at a reduced rate and fortify it with Pro-TeKt 0-0-3, achieving the same thing as a reduced N rate. This plan will keep P & K levels adequate, while reducing the N delivered. This has the added benefit of also including the silicon in the Pro-TeKt for a stronger plant, more resistant to cultural adversity.

Al

Here is a link that might be useful: More here

"I also mentioned that you can still use a 3:1:2 ratio at a reduced rate and fortify it with Pro-TeKt 0-0-3, achieving the same thing as a reduced N rate. This plan will keep P & K levels adequate, while reducing the N delivered. This has the added benefit of also including the silicon in the Pro-TeKt for a stronger plant, more resistant to cultural adversity."

I'm getting lost. So using the same MG 24-8-16 with the Pro-TeKt reduces the N? Would that mean the Pro-TeKt shouldn't be used at first when the plant needs the N? I think I'm tired after a weekend of planting which I havn't even finished yet. I know MG has box with the big tomato on it supposedly for tomatos. Should that not be used when they begin fruiting? I think its a 18-18-21. I still have some from last year. I also have the dyna-gro which I think is 7-9-5. Would that work? (I realize that question doesn't fit here)

Let's imagine you need to deliver 6 units of fertilizer in your program. If you're using 6 units of 3:1:2, it works out nicely that there will be 3 units N, 1 unit P, and 2 units K, for a 6 unit total. Now let's say that you wish to reduce the amount of N you deliver so the tomato plant slows vegetative growth & puts energy into fruit/flowers. If you apply 4 units of 3:1:2, you reduce the fertilizer delivered by 1/3 across the board. Since plants use about 4 times as much P as K, and the ratio is 1:2 in a 3:1:2 blend, we can DOUBLE the amount of K the plant receives and still maintain a very good ratio of P:K. Adding the 0-0-3 ProTeKt keeps that balance more in line with plant usage and, along with the K, offers the added benefit of providing soluble silicon for stronger plants that are more resistant to cultural adversities.

Changing gears: 18-18-21 is VERY close to a 1:1:1 ratio, but you see the blend recognizes the need for a little extra K. You could easily add a little K (potash) to the soil and use a 1:1:1 fertilizer like MG 20-20-20 or other with the same results as their tomato formula.

Al

I sorta understand and I sorta feel stupid. Assuming I deliver 6 units of fertilizer to the plant as in the 3:1:2 as normal fertilizer. I then cut that by 1/3, would that be 2:.6:1.4 (2/3 of original). I understand the N is reduced. If I add 0.0.3 then the amount would be 2:.6:4.4? If P is the middle (.6) then not sure I understand the plant needs 4 times as much P (.6) as K (4). Maybe I have the P & K backwards. I am also assuming to achieve this I would use 2/3 TBLS instead of 1 TBLS per gallon or whatever the recommended amount is. Hopefully you can tell where I am making my error. I want to thank you for taking the time to get my head straight as I actually find this very interesting.

If I say that plants use approx twice as much K as P, does that clear it up, or do you need numbers?

Al

Thank you, that does help. I had it backwards. I guess what throws me off is the bloomboosters that seem to have twice as much P (middle number) as K (last number). Not sure why I always thought they needed more P than K, but thank you very much. I need to have to talk with my 32rd grade teacher about the timeses and gusintas she taught me.

Wouldn't that be a little like learning about calculus from your dentist? You just don't know WHO to trust any more. ;o)

Al

Not sure why I always thought they needed more P than K,

It isn't your fault really. The market is filled with misleading products and claims.

The idea behind a high P fert is that P is believed responsible for the processes resulting in blooms. I am not sure who originally popularized the idea that 'if a little is good, a lot is better', but they got it wrong.

Unfortunately the belief that providing high doses of P will increase blooms has stuck around and nearly everyone makes a high P fert, even companies that know better because the market now demands it.

The cruelty is that the high P fert sometimes can work to increase blooms, just not the way we would like. The over abundance of P interferes with other nutrients to the point the plant gets stressed out.

With many plants stress puts the plant into 'reproduce before I die' mode. We get those flowers, but the plant's health goes downhill as a result. For a short season annual prolly no big deal, but for plants we want around for years to come a very bad idea.

"I am not sure who originally popularized the idea that 'if a little is good, a lot is better', but they got it wrong."

It was my mother!!!!

High P fertilizers are historical carry-overs from the days when most plants were started in outdoor soil beds and the ground was usually still cold at sowing. Cold temperatures reduce both P solubility and plant's ability to assimilate P. It was held that high levels of P in soils helped ensure that at least some P would be available.

I think I'll do a thread on high P fertilizers when I get a chance.

Al

Does that mean in the ground it works ok? Also, you never did get to the issue of Epson salt, lol. Don't think this belongs here either but seems to be alot of talk hydrogen pyroxide. Maybe you could address those some time in the future as well. I look forward to your next article.

Fertilizing plants in the ground is pretty much a crapshoot w/o a soil test to tell you what's needed. No one can really tell you what the best fertilizer is w/o some analysis, but if I had to choose a fertilizer for a 'shotgun approach' I'd still stick with the 'all-purpose' fertilizers in the 3:1:2 ratio followed by the 1:1:1 or 2:1:2 blends.

What was your Epsom salts question?

Al

I had noticed above you said you would talk about epson salt after you found out what fertilizer acidrain was using (your second post I think). I wasn't sure if it was important though but thought I would mention it again incase it was.

He said "Miracle Grow 24-8-16 all purpose is what I have." and you were asking about comments re Epsom salts.

First let's establish that MG 24-8-16 contains no Mg, and supplying Mg is why we would use Epsom salts. To decide if it's appropriate to include Epsom salts in our fertilizer program, we need to know if the soil we are using has had either dolomitic (garden) lime added as a pH adjuster and a Ca/Mg source, or in the case of gypsum - as a Ca (and S) source. If dolomite was used, then it's likely there would be ample Mg (and Ca) in the soil for a grow season or more. If you made the soil and chose to use gypsum as a Ca source, it would not include Mg and it should be added when you fertilize (in the form of Epsom salts, usually).

You should not add Epsom salts to soils unless you know or suspect there to be a Mg deficiency, because Mg is antagonistic toward Ca and can block its uptake when the ratio of Ca:Mg gets much below 3:1. It's better to add Garden lime or a supplement that contains the correct ratio of Ca:Mg than to add Mg (Epsom salts) alone.

Al