The weather can still be very cold in April and so it is important to distinguish between the hardier veg and the more tender.
In sheltered areas in April you can plant outside the hardier vegetable such Broad beans, beetroot, carrots, Swiss chard, summer cauliflower, kohl rabi, lettuce, leeks, radish, turnip, spring peas and perpetual spinach.
The more tender vegetables need to be protected and germinated and grown on under glass, in a greenhouse or conservatory. If you are growing the more tender vegetables such as courgettes, squash, peppers, tomatoes, cucumbers, aubergines, celery, celeriac, french beans, sweetcorn and globe artichokes, they will need to be grown in frost free conditions until ready to be planted out in the veg plot from Mid May on-wards, when the risk of frost should have passed, depending on where you garden in the country.
One of the problems when growing from seed is that the seedlings can get leggy. To prevent this, if germinating using a propagator, remove as soon as germinated to avoid conditions which are too warm. If germinating on a window sill, it is important to physically turn the seedling container around because when the light source on one side, i.e. a windowsill the seedlings will grow to the light which can make them leggy. By regularly turning the pot around it helps to reduce this.
April is also a suitable time to sow in the greenhouse, for planting out later, Peas, beans-French Green and Runners. To avoid gluts later in the season, sow at regular intervals so the plants flower and fruit at regular intervals. All peas and beans need a long root run and are best in root trainers which are quite expensive, or toilet roll holders which are cheap. Tips and advise on growing peas and beans .
The planting order for the bean family is Broad Beans can be planted out in April they are the hardiest of the bean family, followed by Runner beans and French beans if it is sheltered or in May with frost protection.