This is a quite complex question. You are asking about a lot of different plants with different needs. Suffice to say you'll need a lot more than one extra tray. Each plant will need potting up into something small, about the size of a yogurt carton. Then they'll need either potting on again or planting out in the garden. You don't say where you are located so it's not possible to say what lighting requirements you will have becasue we don't know how much longer your plants need to be indoors.

The rockwool cubes weren't really a good place to start. In future you would do better to start in cells or modules in a seed mix. Things like Arugula, Nasturtiums, Cilantro and Sunflowers would be happier just started off outside. Arugula and Cilantro both tend to bolt quicker if transplanted. Lemon Balm, and Thyme are perennials and you would need to be a big consumer of them to need more than one or two plants.

Agree there is no simple answer to your question as there are far too many things involved.

Germinating in rock wool cubes is an unusual approach unless one is planning to grow them hydroponically. If that is your plan then I'll suggest you post over on the Hydroponics forum here.

If the plan is soil growing then all the plants need to be transplanted ASAP - rock wool is short lived and has no nutrient support for anything with true leaves - into containers of soil-less potting mix ensuring that all the RW cube is fully surrounded and covered by soil. The size of the containers needed will vary greatly for each plant and there is simply no way 1 tray of equal sized cells or pots can accommodate all those plants equally well. What size cells/pots in that tray?

2" tall seedlings of herbs can go into a 2" container for now, but things like tomatoes, melons, and especially sunflowers would need 3" pots minimal I think and that won't be big enough for long.

It is really difficult to say what is best to do without seeing at least a photo of the plants. as it is quite a hod-poge of plants all with very different needs.

Dave

I guess I was given some bad advice.

I mixed some soluble fish fertilizer with water and have started to use that to rewet the rock wool. It's at a reduced strength (instead of 2 tablespoons per gallon I used 2 tsp, or about 1/3 strength.

Here's what they looked like just before adding the fish fertilizer:

In 6 or so weeks this will all be transplanted into raised beds, once it's warm enough.

Are you planning to separate those tomato seedlings or just snip off the extras? Trying to separate in rock wool is difficult to do without killing the extras so snipping is the usual approach. But either way it needs to be done ASAP as they are already getting leggy and entangled.

Next year I'd strongly recommend direct seeding all the flowers, especially the sunflowers, and the herbs too for better results.

Dave

For your future...I collect plastic cell paks of all sizes, from one inch cells to 3 inch cells, and use a good seed-starting mix. I start seeds in the size cells that will hold the seedlings until time to be planted out. This way I never need to transplant anything. I keep notes and have lists of when to start each plant based on weeks before or after frost dates. You get to know all this with time and experience (take notes) and reading seed starting lists.

" I start seeds in the size cells that will hold the seedlings until time to be planted out. This way I never need to transplant anything."

Please note that as often discussed on many of the forums here that approach is not recommended with many seedlings as it is the act of that initial early transplant that triggers feeder root development. It is also possible for young seedlings to develop root rot when first germinated in overly large containers because of the water table that develops in disproportionately large amounts of soil.

Dave

Dave, my containers are not overly large and I bottom water. They are seedling cell paks and the roots are just fine. I've been doing this under lights for 40 years, maybe different for my home garden than for a big business like you are involved in.

FWIW, here's what they look like now, replanted. Separating them was tricky but they all made it through the process.

Well they certainly look a lot better than last time we saw them ;-) Peat pots are not a popular choice on this forum but yours seem to be doing the job at the moment. When you plant out don't believe what the pot manufacturers say. Roots have a difficult time penetrating the pot walls and the peat wicks out moisture. Tear the pots off before planting out.

Will do, thanks.

They're growing like gangbusters.