Well assuming that both have all the 3 basic N-P-K just at different levels, it isn't going to make much difference. The plant will only use what it needs assuming all 3 are available. Hopefully they also contain the needed micro-nutrients.

But at only 18" tall those are very small plants and they need much more growth and root development before they can cope with fruit production. Early fruit on small plants is often prone to BER anyway and gets tossed. So I'd go with whatever the mix is that you are calling "vegetative stage nutrients".

Dave

When growing in the soil you really want to get a soil test to determine what, if anything, needs to be added for strong, healthy plant growth. For a home grower a soil test once every 5 years or so should be sufficient.

It's pointless to use a fertilizer that contains a nutrient if your soil already has an excess of that nutrient.

While plants can 'take what they need and leave the rest' to a point, it's not an absolute rule. Excess nitrogen will cause too much vegetative growth that isn't hardened properly to have any resistance to disease. Excess phosphorus around the roots may compete with N and K and definitely will produce deficiency symptoms for iron and zinc. Excess potassium competes with calcium, possibly magnesium as well.

It's darn difficult to undo an excess of most nutrients so it's best to not add too much of anything. A soil test will let you know what does and doesn't need to be added. It *should* come with specific recommendations on what to add (or not add) for every nutrient tested. It will also tell you the soil pH and what, if anything, should be used to adjust it for optimal nutrient availability for your garden.

I agree with everything jag said above but if I recall correctly from your other posts you are growing in containers and a small raised bed, correct? My reply above is based on that recollection.

If I'm correct then your need to feed is greater than with an in-ground garden and your soil nutrient levels are pretty much pre-determined by the mix you are using.

Dave

Only N in NPK is a problem. You have to have just the right amount of it. Since it is water soluable, plants will take whatevere is there. If you have too little, your plants will not have vigor. I you have too much, you will get a lot of foliage, not much bloom and fruit.

Phosphorus attahes itself to soil and it will not be washed out and excess of it will not harm. Potash is between. Also excess of it will not do harm. But nitrogen is critical and has to be given as needed.

In my opinion and undrstanding, in a well establishe garden, with application of organic mater, there should be minimal need for phosphorus and potasium. But nitrogen has to be applied continuously and moderately, since excess of it will leach out, as it is water soluable.

Once my fruiting vegatable are established and are of healthy green color, I would use mostly the fertilizers high in P, medium in K and very low on N. With veggies that are not supposed to bloom or bear fruit, I will avoid Phosphorus. That is how I do it in my herbs gardem, mostly nitrogen and some potash.

I agree with everything jag said above but if I recall correctly from your other posts you are growing in containers and a small raised bed, correct? My reply above is based on that recollection.

I do a lot of container growing. I also use raised beds for veggies that are loosely based on 'Mel's mix' which is 1 part compost, 1 part vermiculite and 1 part sphagnum peat moss. This is only 6" deep and underlying it is a mostly clay soil. I also used earth based gardens that are clay soil based, though not so much for veggies.

In containers I use a hydroponic fertilizer which contains all known essential plant nutrients plus silicon, but in the raised beds I use nothing other than compost and soybean meal. The soybean meal is meant only for it's nitrogen value. The clay soil/compost supplies enough of everything else.

In the earth based gardens I also use soybean meal as the native soil has enough of everything else and occasional applications of compost keep it that way (I say this pending the next soil test result).

Anyway, I agree with what you say, but do put qualifications on the 'plants take what they need and leave the rest' idea. If we assume the ground soil has a moderate amount of NPK and we use a 10-10-10 fertilizer we can expect plants to do well for many years. They will continue to do well until the phosphorus being added in the soil builds to an excess (because plants use so little of it compared to N and K) at which point it interferes with the uptake of several nutrients, iron and zinc being the first. Unfortunately iron deficiency is extremely easy to confuse with nitrogen deficiency. Adding more N incorrectly would make the problem worse.

The idea that plants can regulate their nutrient uptake comes partially from the fact that in a mineral soil most nutrients get 'bonded' to the soil (mostly clay or organic matter) due to their ionic charge as well as the strength of that 'charge'. Beyond this plants take up water and any nutrients that have become soluble in that water regardless of the ratio.

This is how/why nutrient imbalances occur.

In other words plants really don't have a great ability to regulate nutrient uptake, it's mostly the soil that regulates what is plant available and once the soil's capacity to hold onto a nutrient is exhausted, the plant will take up anything and everything dissolved in the water around the roots including lead. They have no ability to separate a potassium ion from a nitrogen ion. It all enters the plant via osmosis with the water and then the plant has to deal with it and the growth governing effects.

Although N-runoff gets the most publicity, a quick search shows that P-runoff is also a problem. Reservoirs and surface waters can be polluted with phosphorous.

Compost is always the best option, since release from compost is slow and generally plants thrive in it. K is easily supplied from wood-ash, if needed. Tomatoes especially grow really well in quite fresh, relatively unfinished compost.