Sweet Peas can be successfully grown in containers following a few basic rules:
- Sweet Peas have a large root system and will need a minimum container of 20 litres providing 7 litres per plant for Spencers and 5 for Old Fashioned.
- Keep well-watered with good drainage and water every day it does not rain. Fully grown plants may need water even when raining as the foliage deflects water away from the container.
- Provide a nutritious growing medium with good moisture retention properties.
- Plants growing in containers will need a weekly feed, something with high nitrogen eg. Miracle Gro, from about 4 weeks after sowing. Once flowering, swap this with a high potassium product, such as a tomato fertiliser.
Ensure good drainage holes in the base of the container and add a 2-3cm layer of coarse aggregate (not limestone) in the bottom.
Preferably use a 50/50 mixture of good garden soil and general-purpose compost, with 10% of the volume made up with well-rotted manure or use a slow-release fertilizer. Fill the container to 5cms of the rim and top off with neat compost to provide a mulch.
Sow seeds as for normal planting in the ground or directly into the container from the end of March. Protect germinated seeds from birds. After germination, add the support structure.
If netting is used as a support structure it will need to be draped from a height - a wall or fence and anchored to the container. If growing against a trellis some strings or net will be needed to train the immature plants onto the trellis. The most common supports are canes long enough to support the type of Sweet Pea grown. These can be placed round the rim at 20cm intervals and tied together at the top to form a wigwam. Garden twine is then tied round the canes to form a stable structure. Alternatively create a cylinder - erect the canes vertically with their tops attached to a wire or plastic ring, only slightly less in diameter than that of the container. Wind twine around the canes. This form will contain the growth better than a wigwam.
As with growing Sweet Peas in the garden, it is essential to remove the flowers as they appear to keep continuity of flowering.
Intermediate varieties need the same growing medium but with shorter supports. Dwarf varieties need no support at all and will grow very successfully in low troughs.