Fertilizing even non-grafted seedlings is hotly debated. Only consistent recommendation is if you do make sure it is well diluted stuff - like 1/4 strength.

Just as when growing clones/cuttings, fertilizing grafted seedlings is another added stress - root development is the goal at this stage, not top growth, and added stress only reduces root development.

Sooo I wouldn't feed them until new top growth as sprouted on its own or until they are transplanted out of the 6 packs and into larger containers and settled in to them. JMO

Dave

Hotly debated, agreed ;-)

Why not fertilize them at 1/4 - 1/2 strength after a week or ten days recovery ... being more concerned about top growth for a graft? The roots are supercharged and the mending is up top (including stem). I think by the nature of the aggressive roots, they would eventually surpass their growth requirements. But probably the rate and when you fertilize will depend on the fertility and maybe type of the starting mix.

PC

I wouldn't hurry to fertilize. I didn't fertilize for 17 days after grafting. On day 18 I didn't actually "fertilize" but did pot up and the additional potting mix has nutrients.

I guess I didn't realize fertilizing tomato seedlings was such a debatable subject. My growing mix has zero nutrients added and I fertilize with deionized water, so these seedlings are relying almost entirely on their seed reserves. I'm certain they'll need some nutrition soon. I think 1/4-1/2 strength once these seedlings begin to show top growth is good advice.

Just an aside, isn't the root/shoot ratio more or less fixed? If top growth is encouraged with fertilization, won't additional root growth follow?

My original growing mix DID have nutrients, so my situation is different than yours.

isn't the root/shoot ratio more or less fixed? If top growth is encouraged with fertilization, won't additional root growth follow?

No it isn't fixed. They have different triggers. You need top growth to follow root development, not the other way around. It is the roots that supports the leaves rather than vice-versa. When transplanted for the first time the development of fibrous feeder roots is triggered.

Assuming that pre cutting soil had already some nutrients, the immediate fertilizing maybe is not an urgency.. I will wait until the graft is established then, like Dave said, feed 1/4 strength, and once they go in a bigger pot, I would up the strength to 1/3 strength.

Seysonn

Your plants require nutrition now since they are in an inert medium and need to repair themselves at this point, which is already 10 days following the grafting and they've already recovered as much as they can in this time. If you have Dyna Gro 9-3-6, I would irrigate with about 0.4 teaspoon of it per gallon on the first irrigation, then skip and then continue with 1/4 teaspoon per gallon. This is a very low rate. This fertilizer is high in nitrogen/low in phosphorus for my taste, but it still should work and has excellent soluble ingredients. By about 0.4 teaspoon I mean 2.7 grams per gallon by weight which is more precise. Also you need to be sure calcium and magnesium are added since the fertilizer is very low in them, whether by switching to a safe tap water or maybe mineral water from a gallon with the Ca Mg analysis.

I have put two graftsin much higher fertilizer rates (because they shared the irrigation with maturing transplants when I did it.) That was not a good idea but it is worth saying both did well and one became a reasonable plant, while the other died due to just messing around to learn (it was Better Boy on CP, the reverse of the CP on BB which was cared for).

It does look to me like the plants got something out of the starter mix, but taking into consideration what you've said, IMO this is the best strategy.

PC

Thanks to everyone for the advice. I fertilized as per PupillaCharites' instructions and the grafted plants are starting to push out new leaves nicely.

Congrats on the success ferro, if you are sure the union is well healed over, it is probably a good idea to not let the temperature get too warm (keep below 75 F) but mostly take your cues from the appearance of the plants (to keep a reasonably low height:stem diameter ). They look nice!

PC

They are in a fairly well controlled growth chamber at 24 degrees C (75.2F). It might be a degree or two warmer when the lights are on. There's also an oscillating fan in there to hopefully strengthen the stems. Hopefully they don't get too big before it's time to move them outside.