Leif
I’ve noticed a very big difference this year between mid-March sowings and early April sowings, irrespective of whether I’ve sown in the soil, sown in modules in an outdoor lean-to mini-greenhouse or whether I’ve done it in unheated propagators indoors with lids on.
Beetroot:
Boltardy sown 16/3 indoors in modules – germination time: 12 – 16 days;
Boltardy sown 24/3 in a sunny area of soil – germination time 13 – 18 days+ (still a few gaps in the row);
Pablo sown 5/4 indoors (2 days after full moon on a Maria Thun root day): >90% germination of 60 seeds in 15 modules within 6 days.
Radish:
Nelson sown 06/03 in between garlic rows – germination time: 15 days +;
Nelson and Prince Rolin sown 24/03 between garlic rows – germination time: 11 days +;
Nelson sown 05/04 in between parsnip rows – germination time 6 days+ (about 12 seedlings already through in a 3 metre row);
Cabbage and Cauliflower:
Durham Early and All the Year Round sown 13/03 in modules indoors – 10 days to germination;
Landini F1 sown 08/04 in modules in outside lean-to greenhouse – 4 days to germination;
Lettuce:
Lollo Rosso Red and Bionda a Foglia Lissa sown 13/03 in an unheated propagator indoors with lid – 7 days to germination;
Bionda a Foglia Lissa, Lollo Rosso Red and Passion Brune sown 02/04 in the identical unheated propagator also indoors with lid on (two days before full moon on a Maria Thun leaf day) – 4 days to germination;
I”m based in NW London so probably slightly colder nights in late winter/early spring but perhaps slightly warmer days.
My lean-to was under £50 and has four shelves of about 2m * 1m. It has loops to allow you to tie it to something solid as it will blow away/over in the wind when it isn’t weighed down on the bottom shelves with something heavy (like a deep tub germinating leeks).