I have several trays of sweet pea in the green house at present, they are about 6 inches in height, i also have a polytunnell, and wonder should i transfer them there, will they keep growing ,and should i put them in to larger pots, i read about a trial being done , some sown in april, and the rest in Oct. and the latter were the best .
Seeds can be sown directly where they are to flower in September or October, because sweet peas are hardy, although, taken directly from the greenhouse, they must be hardened off before planting outdoors. This was usually done in a cold frame and the tunnel would be a bit warmer.
Harden them off in spring in a mild spell before planting out by putting them outdoors by day for ten days or more and taking them in at night.
In any case give them good light and pot on the plants if they are outgrowing their pots. Watch for snail damage.