Once the seed has been sown, these should be removed so that they don't damage the emerging seedlings. Alternatively, a cloche can be used. It can be left in place after sowing because the emerging seedlings will have plenty of space beneath it. Plants grow quickly in these protected conditions and mature before those sown in open ground. Water plants under the cloches as the soil can become quite dry.
Ventilation is also vital because still air can create the perfect conditions for fungal diseases.
If space is limited, sow in deep beds. Vegetables can be grown closer together, which increases their yields. Dig the soil deeply, working in organic matter such as well-rotted manure. This raises the ground and improves drainage. The extra soil depth promotes strong root growth.