With a magical scent and an ongoing sea of bright flowers it’s not surprising that annual Sweet Peas are one of the most popular summer plants. The plants will only last until the weather turns colder but you can save the seeds to grow more the following year.
When to sow Sweet Pea seeds
Seeds can be sown in either Autumn (in a frost-free place such as a covered cold frame), or more commonly in late winter/early spring (on a sunny window sill or heated greenhouse).
How to sow Sweet Pea seeds
The seeds themselves may benefit from a soaking overnight (or a few hours at least) in warm water, this softens the outer shell of the seed making it easier for the seedling to break through. Some people also advise very gently scoring the seed with a sharp knife (but avoid the ‘eye area’). Every experienced sweet pea grower will have their own method and tell you it’s the only way to do it – find what works for you.
Prepare your pots or trays with good quality seed compost, make sure you use pots that are fairly deep (7cm at least) as sweet peas produce a long root ball. Leave a space of at least 3cm between seeds and plant and at a depth of 2-3cm. Keep the compost moist and you should start to see seedlings in a couple of weeks.
Top tip – empty toilet rolls make perfect containers for sowing sweet peas. They have the ideal depth for the roots and will quickly break down when transplanted outside so there is no need to remove the seedling first (and therefore no risk of damaging the roots).
You can also plant Sweet Peas directly into the garden using the same method above however, this should be done after all chance of frost has passed which in this area can be April/May. This method delays when your plants will start flowering and, mice love sweet pea seeds so you may need to keep them protected.
Where and how to plant out seedlings
Once your seedlings are about 10cm tall pinch out the tips to encourage bushy growth. If grown inside you’ll want to harden them off, place them outside during the day but bring them back in at night to avoid them being exposed to the cold. Frost will kill or severely damage your seedlings so ensure all chance of it has passed before planting them outside.
Sweet Peas do just as well in a container as they do in the ground, just ensure that they have enough depth for their roots (min 40cm) and plenty of support. They prefer a sunny position with good drainage but don’t let them dry out.
Prepare your soil with a good slow-release fertiliser or, use a good quality compost to fill your pot with. If planting in a pot it can be good idea to put something heavy in the base, due to the height sweet peas reach they can be prone to tipping over in strong winds.
Taking care not to disturb the root ball transplant your seedlings, space them out about 20cm apart and give them a good water in.
Supporting Sweet Peas
Sweet Peas must have support to grow. This can be anything from a wall, trellis, bamboo canes – basically anything with sufficient height (check the seed packet for the maximum height of the variety you are growing). You will need enough space to attach and train the plants, this can be done by making a structure with garden twine or using smaller pliable branches. If planting in a round pot making a teepee with bamboo canes is ideal.
Sweet peas produce tendrils to attach themselves to any support, you can just leave these but most experienced sweet pea growers will tell you to remove them. Cutting off the tendrils (where they meet the flower stem) causes the flower stems to be longer and produce more flowers. If you choose to do this you will manually have to attach the plant to the support. Garden twine, wire or even plant rings/clips are perfect for this.
How to care for Sweet Peas
Sweet peas need energy if they are going to keep producing flowers for you, the fertiliser/compost when first planting will keep them going for a few weeks but once they start flowering, they really need a weekly feed with a high potash fertiliser. Liquid tomato food is perfect for this – just follow the instructions on the back of the bottle.
Don’t let them dry out, check them regularly especially in warm weather. Sweet peas prefer a thorough soaking every couple of days rather than a light drizzle every day.
Keep picking and/or deadheading
The more flowers you pick the more you encourage the plant to produce more. Sweet Peas are excellent cut flowers and, if you have picked a highly scented variety, they will make your home smell divine.
If you don’t pick the flowers or, have some on the plant that are starting to wilt then remove them asap. Once the flowers have died the plant will put its energy into producing a seed pod where the bloom was. If removed the plant will instead use energy to produce more flowers.
Get free flowers next year
Once the season is almost over and the plant is starting to show signs of slowing down you can get it to produce some seeds for you to use next year. Allow a number of spent flowers to die off on the plant, seed pods will then soon appear. Leave them on the plant until they turn a light brown colour. During a dry day collect the pods and remove the seeds, these can then be stored in a paper bag or even envelope until next year.
Top tip – it’s always a good idea to write on the envelope/bag what the seeds are and the variety if you have more than one type growing.