Sickly beetroot

We start our beetroot in pots, a couple of seeds in each pot and then they go out as soon as they look big enough. We sow them in batches so the beets are ready through the season. Our first batch of beetroot started off well, but much of the young plants have keeled over an died. We have taken the remaining ones to the greenhouse in the hope that they will like the cooler space. We have sown a lot more to try to catch up.