Plant evaluation numbers

What is the general consensus on the number of plants needed to give a reasonable evaluation of a single cross.

For the first time I will have hundreds of seedlings from 1 cross and need to limit nos to save space as all my work is done on 2 benches in a small backyard.

I sow into trays 350mm X 300mm (up to 1500 seeds) then transplant at 1st leaf into 50mm x 50mm pots until first flower. The selected plants then go to 100mm X 90mm until 2nd flowering, survivers then get a 100mm X 140mm deeper pot for the rest of first season

As space is so limited I need restrictions on all unnecessary plants to allow for later developments.

Any advice?


Somewhere some geneticist described in the RHA newsletter, perhaps 30 yr ago, that about 100 seedlings lets you see the range of things, if there is independent segregation of traits. So leaf shape, flower color, petal number etc may give you an idea with that many plants. But what you need usually is the really rare bird.

Why not crowd them? I grow 144 seedlings to bloom in a standard 9 x 18 inch flat of six-paks. You won’t get good measures of plant dimensions but flower color, petal number leaves from seed to flower can be seen reliably enough for the first cull. And of course disease resistance is really challenged with that kind of crowding. So you can do 1000 seedlings in under 10 sq ft. For floriferous crosses 3/4 of surviving seedlings bloom. Not all seeds that germinate actually produce true leaves in my experince when transplanting sprouts from the straatification medium. So you may see 500 flowers in 10 sq ft.

Cull brutally (up to 90 %) based on color, petal shape or number, disease (esp mildew) in that first round of flowering and you’ll only have to use the same bench area for the next round. That’s roughly 4 inch square pots, which is good enough for a whole summer in many climates.