How many days can you leave a bean plant grow in this container after the seedling has emerged. Before you need to get them into the ground without them becoming root bound in this tray.
Because of my temperamental Spring weather, I start a lot of bean transplants. I use Peat 32's for common beans, most limas, and runner beans... and 3" pots for the largest limas & runners. For the limas & runner beans, I try to transplant them as soon as the first pair of leaves is fully grown. For common beans, I wait a little longer - when the first true leaf has emerged (about 14-21 days after planting). Some years weather delays transplanting, and the beans begin to form runners... at that point they will often be slow to establish, and may or may not fully recover. Even in the most extreme cases (such as in 2020, when I actually had to prune back the 2' runners) the over-grown transplants will still produce dry seed, under conditions which might otherwise have caused failure.
I start all runner beans as transplants now, because the emerging shoots closely resemble walnut shoots, and squirrels will dig up the whole row.
For peas, garbanzos, cowpeas, yardlong beans, and most smaller beans, I use peat 50's. Cowpeas get leggy quickly, so I try to transplant those as soon as the first two leaves are fully grown... and because germination can occur in as little as 3 days, transplanting might only be 7-10 days after planting. Peas & garbanzos take longer to germinate, grow more slowly, and can stay in the pots longer... so transplanting is anywhere from 21 days or longer after planting.
I use peat pots for most beans because the roots grow through, and are not air pruned or root bound. I even poke extra holes in the pots with an ice pick, to encourage greater root penetration. A little sand in the bottom of the tray helps to keep those long roots from drying out. When transplanting, those roots can be gently pulled loose... if coiled into the planting hole & not allowed to dry out, those extra roots greatly minimize (or eliminate) transplant shock, and the seedlings become established almost immediately.
Soybeans germinate more slowly & form a stronger root ball, so I use plastic cells for those - deep 36's. Those transplants proved their worth this year, allowing me to save 4 old soybean varieties which had completely failed the previous year. I will be repeating that process for the three varieties which had 0% germination in the garden this year.
Transplants are a great way to revive old seed (or to make every seed count from a small sample) because you have greater control of conditions.
