Cauliflower Seedlings Demise

I sowed some seedlings (all year round) in a heated propagator.  They germinated very quickly after a week I took them up to the greenhouse. I noticed that they were not growing well. Whilst the other seedlings i.e broad beans, chilli's were putting on growth. Eventually they give up the ghost the leaves looked scorched and withered. The weather has been quite good this spring so the greenhouse has been quite warm in the day. Do the cauli's need a cooler environment? As the other plants that like warm conditions i.e tomatoes chilli's and cucumbers are doing fine.

They don't like it hot like any other brassica.

My greenhouse got up to 48 c one day last week even with the door open.

My guess is that it was too hot for them in the greenhouse. Mine have been in a cloche in the back garden since mid March, with the vents open since early April. Even the odd frost with ice on the inside surface of the polythene hasn't bothered them in the slightest. They are very hardy.

We stress on the forums more times than I care to remember that brassicas hate heat. At the most they only want gentle heat. I do my early ones in just a frost free greenhouse. The heat should certianly be reduced as soon as they have germinated. At this time of year they will only see the great outdoors, even at the sowing stage.

Quote from: DD. on April 30, 2014, 07:13

We stress on the forums more times than I care to remember that brassicas hate heat. At the most they only want gentle heat. I do my early ones in just a frost free greenhouse. The heat should certianly be reduced as soon as they have germinated. At this time of year they will only see the great outdoors, even at the sowing stage.

I've seen this advice this year in particular, and mine were sown in pots and put in my blow-away GH inside my proper GH, which did get quite warm! Despite that, they all germinated and are looking very healthy, so they are now outside during the day to harden off as I have no cold frame. Have I just been lucky or what?

My suggestion might be that the double layer greenhouse has reduced the sunlight so they haven't burned.

I don't think you will have needed a cold frame over the last few days as its never been really cold - although frost is forecast for the weekend.

I grow my plants in a "small" amount to be strong and sturdy. I don't grow them in a large quantity as fast as I can for a quick turn around to sell to an unsuspecting public!

Quote from: Headgardener22 on April 30, 2014, 14:00

My suggestion might be that the double layer greenhouse has reduced the sunlight so they haven't burned.

I'm inclined to agree. My local nursery grows them in opaque poly tunnels until the seedlings are 2 or 3 inches high with the industrial gas heaters blasting away. It is positively tropical in there. I'm not sure what the actual temp is, but you don't want to wearing a coat. They then go outside for sale in April in a big open sided shed with a shaded roof. 

I wouldn't argue with DD though.

The plants being sold at the garden centres now are junk. Leggy, and weak, because they have been growing in a heated polytunnel with lower light levels. Grown slowly, with maximum natural light and brassicas will grow stocky and strong, ready for any weather.

Rowan,  what varietys were you growing in Kenya?

Totty

Quote from: DD. on April 30, 2014, 07:13

We stress on the forums more times than I care to remember that brassicas hate heat. At the most they only want gentle heat. I do my early ones in just a frost free greenhouse. The heat should certianly be reduced as soon as they have germinated. At this time of year they will only see the great outdoors, even at the sowing stage.

Never had any issues growing Cabbage / Broccoli / Kale in Kenya. I could turn round a 5lb cabbage in 16 weeks at 25 degrees C ave. day time temp with highs of unto 40 degrees c and harvested probably 20-30kgs of Kale per day from a  small area. Seedlings were started in a plastic hoop house, must have been 40 degrees daily. I think the generalisation that Brassicas hate heat is OTT. I certainly wouldn't suggest however that there is any need to specifically heat brassica seedlings and they will most often be happy outside in the UK.

Some differences between Kenya and the UK are the sunlight is much stronger, the daylength in the "winter" months is much longer and I suspect there is less of that horrible dull perma-clag type weather that often plagues the UK in Spring and Autumn. I wonder if it is not so much the temperature alone but the balance between temperature and sunlight that dictates how the plants grow. In the UK if the temperature is artificially kept high but with the low light levels typically seen in early spring the seedlings will grow quickly but then race to find adequate light hence they grow leggy and weak.

Just my thoughts. Are you growing varieties that have been bred for hot climates?