For that size pot - assuming they will be transplanted again later to a larger one - I use 3, maybe 4 plants if they don't separate easily.

Dave

When I sow Lobelia, I tend to sow them really densely, which makes it near impossible to separate them individually. I simply tear the clump into thirds or quarters and repot those. Then usually, when planting them out, tear that clump into sections too. I probably have more like 10-20 in each clump, but they are going into the ground, not into baskets.

I use a lot of lobelia as edging in my kitchen garden and in the front of flower beds. Love that intense blue!

At what point do you separate the lobelia? I sowed mine densely too, since I had an abundance of lobelia seeds.

I deal with them differently than Dave, but I grow only about 3 packs of seed, he's a pro probably grows dozens of trays

I usually sow mine in 3 oz cups. When they start looking crowded, flowing over the sides, I divide the clumps in thirds or quarters, and pot them into the same size cups. where they stay until I plant them out. By then they are usually over flowing the sides again.

My way is much rougher and I know I lose some, but its fast and easy and works for me.

I use a loose soiless mix and plant my lobelia seeds fairly thickly. I thansplant when they have true 2nd true leaves. I keep a margarine container on hand filled with warm water. I plant 3 to 5 plants to a 2 inch square -6 pack. I soak the container I've grown them in so the soil is wet. A plant separates from wet soil easier than dry soil. If the plants separate easily they go in with what soil they have on the roots. If they don't separate easily instead of tearing the roots I swish the roots of a clump of them in the margarine container of water washing off some of the soil and saturating the roots and they usually separate quite well then I poke a hole in the new soil for the roots and cover them in. I lose very few plants this way.

I grow them thickly in cell packs, tear them into clumps, and plant them directly into flower boxes as edging plants when all frost is gone. I don't bother with transplanting into bigger containers before planting out.