The Woodside Guide to Growing Sweet Peas
There are many ways to grow Sweet Peas, and this guide is based on advice provided by the National Sweet Peas Society, and personal experience.
Sweet Peas can be grown from seed, or you can purchase them as young plants later in the season to grow on yourself.
If growing from seed, make sure you select the right variety! Most Sweet Peas grow to around 6ft in height, but some are shorter and even dwarf varieties are available, so don’t just go for the pretty picture on the seed packet – read the description too to check the height. Seeds can be sown from January onwards for in our area. There is no benefit from making autumn sowings as our winters are too cold for the seedlings to thrive.
Seeds should be sown and covered with 1 cm of multi-purpose compost – seed composts often have insufficient air spaces and are best avoided. We recommend Growmoor Multi-Purpose with Added John Innes compost. There are three options for containers:
- Put 8 seeds in a 12.5 cm pot, reducing to the best 6 following germination. These can be left in the pots until planting time.
- Put one seed per cell in deep Rootrainers, which have 8×4 cells. These are 12.5cm deep and the plants are left in them until planting time. Rootrainers are available to purchase at Woodside, and are robust enough to be used year after year.
- Put 50 seeds in a standard seed tray, arranged 10×5. Once the seedlings are about 2.5cm high, they will need to be transplanted into one of the above containers for growing on.
Contrary to advice often offered do not soak seeds in water before sowing as this may reduce germination. Germination is best at about 15C to 18C and can take place in 7 to 14 days, so keep the seeds indoors on a light windowsill, or in a heated greenhouse, and protect from mice.
Gently water in your seeds after sowing. Further watering is then best avoided until germination can be seen, in order to reduce the risk of disease and rotting off.
After two pairs of leaves have been produced pinch out the growing tips of the primary stem, to ensure the development of side shoots. This is known as “stopping”, and will give a bushy plant, rather than a straggly one.
Sweet Peas are a hardy plant, so they can be planted out as soon as they are large enough – there is no need to wait until the risk of frost has passed. If purchasing plants that have been multiple sown in a small pot, these will need to be separated out, potted up individually, and grown on until they are big enough to plant out. For planting out, individual plants should be placed in holes and the soil level brought back to a level below the first side shoot and planted firmly but lightly to ensure good soil contact. Sweet Peas grow best in a sunny spot with at least 6 hours of sun each day, but like their roots to be reasonable cool – so don’t plant in a hot place in the garden. They’ll thrive in any fertile garden soil that drains easily. They dislike wet soils and won’t flower well in shade.
Unless you are growing short varieties, all sweet peas will need a support of some sort. This could be a trellis, arch or obelisk, or you could make a post and wire structure or grow up canes or branches. Make sure your support, whichever you choose, is tall enough for the growth.
As growth progresses the stems should be tied to their canes, using rings or soft twine. If you are growing for exhibition Spencer varieties need to have their tendrils removed. Otherwise, leave tendrils in place to allow the plants to climb themselves.
Once flowers appear they should be cut regularly or dead headed to ensure no seeds are produced, otherwise flowering will cease. Feed weekly or fortnightly with a liquid feed diluted to half or even a quarter strength– we recommend Maxicrop organic seaweed fertiliser. Sweet peas are nitrogen fixers, so are good for the soil.
If you are growing plants for exhibition use we recommend that you visit the National Sweet Pea Society website for tips and showing requirements.