Which to pinch and which to leave

I have a large number of seedlings... about 400 give or take... nothing else to do at the moment. Thanks to the good people on here, they are all growing beautifully now. The next dilema.... which of them will benefit from pinching out.
I have:
1. Alyssum North Face
2. Alyssum Wandering Star
3. Cosmos Sonata
4. Lobelia Cascade
5. Petunia Reflections
6. Antirrhinum Sonnet
7. Mimulus Cupreus
8. Cerastium Tomentosum
9. Physostegia Virginiana
If some kind person could run down the list for me I'd be really grateful.

 

I can only help with No. 3. When I grow Cosmos I always pinch out the growing shoot, it make the plant more bushy and stops it going leggy.

 

Thank you @john558 . At what point would you pinch. They currently have 3 pairs of proper leaves.

 

Oh where you see a growing point. Also I do mine when they are at least 12 inches tall.

 

Thank you.

 

Regarding Cosmos, I have tried pinching the tips (which, in my books, is a kind of herbacious cruelty) and non- pinching them. In my conditions, the un-pinched ones get leggier and the mature plants have bendy knees, but flower much earlier than their properly mauled sisters.

Obviously it all depends on the light, timing and temperature so it's a bit of hit and miss. This year I'll go halves and pinch some and leave some unmolested. Apologies for the slightly emotionally charged language

In general, anything that I want to become bushier, gets pinched (this year Sedum, Basil, Bakopa). Anything with a single growing point and no intentions of forming side shoots (Artichokes, Echinops, cacti) are left unpinched.

Pinching is usually best done when the seedlings are growing strongly and have a good amount of proper leaves. When they look like they are roaring, pinching the tip will encourage side shoots. If the seedlings are too young or in a phase of focusing on growing roots, damaging them any way may hurt.

Some pinched tips can be rooted to give more plants for free.

 

Not sure if I should but I pinch everything.

 

I would pinch out....

3. Cosmos
5. Petunia
6. Antirrhinum
9. Physostegia

The others are pretty much ground hugging plants and won't need it. These plants should also be grown on in small clumps, pricking out 5 to 10 seedlings together.

 

@Selleri I've now conjured up an image of you masked and going at your seedlings like a Ninja!

 

Thank you @Sheal ... that makes sense.

 

With Cosmos to get good plants I leave until 6 inch at least
curl the root around the sides of the pot adding more compost as you go continue until you reach the leaves .this gives you a thick strong plant.

 

Do you mean when you pot it on you bury it deeper @Purple Streaks . At the moment, mine look like palm trees!

 

yes I do them deeper.


I bury mine up to their first lot of leaves after burying the roots and stem
I usually have a lot longer root underground to twirl around the plant pot so instead of finding deeper pots I do it this way and for some reason they make better plants.

 

Thank you @Purple Streaks