We always grow parsley in the tunnel, just for superior quality and fast regrowth – much like we do with most of our soft herbs – coriander, chervil and basil mainly.
We aim to have parsley all year, though there can sometimes be a bit of a gap around end of April to end of May depending on how early we have planted the February sowing. We only do two sowings, one in early-mid February and one in early-mid August. The first sowing we plant into the tunnels around early April and harvest through the summer and autumn. We usually leave some of this in all through the year and over winter, but aim to have the second sowing planted in September so that it gets well established and can be harvested through winter and spring. The February sowing usually goes to seed just a bit earlier than the August sowing.
We have always used Italian Giant, which we have saved seed from for the past 4 or so years. We save seed each year – making sure it is not from plants that go to seed early, to ensure that we always have fresh seed to sow, as it does not keep particularly long. We found huge improvements from sowing from our own saved seed for parsley, and there is the added benefit of allowing it to flower, which as an umbellifer attracts huge amounts of beneficial insects. We sow two to three seed per module in West Riding compost, cover the seed with a sprinkling of vermiculite, then soak the trays from the bottom. These are then covered in polystyrene for about 10 days, so that the seed can take in enough water and then the polystyrene is taken off to allow light to get to the trays.
We have started growing some curly leaf parsley too, as some restaurants prefer this as it tends to have a stronger flavour, and so they need less of it. When harvesting parsley we cut the plants right down, a few inches above the soil surface, we weed as we harvest and remove any older leaves from around the plants too.
The only problems that we have ever had is some mildew if the soil is not moist enough, but the plants always seem to grow out of this come spring when they grow rapidly again.