The joy of picking a posy of highly scented sweet peas is one of the highlights of summer for some. To get them growing as soon as possible, you can start sowing now on a warm windowsill or a heated propagator.
You’ll be able to buy young sweet pea plants that were germinated in autumn in garden centres now. You tend to get a number of seedlings in a pot. Sowing sweet peas in autumn gives the earliest blooms. If you’ve bought sweet peas and they look a bit crowded its worth pricking them out into individual pots to give them a bit more space. I’d also pinch out the growing tips so they grow more bushy as they can get a bit leggy at this time of year. You can’t plant them out just yet so either keep them in a cool cover spots, perhaps a porch or a patio cold frame or if not close to the house with some fleece at hand if we get frost. You can plant them out in the beginning of April.
Now you might have bought plants, but it’s also worth sowing some now. Getting the seeds to germinate in the warmth, transferring them to cooler conditions so that they slow down a little and planting them out in early summer. If you’ve bought plants you’ll get an extended period to pick those lovely blooms. The ideal germination temperature is 14-18 degrees Celsius and no more than 21 degrees Celsius.
Traditionally sweet peas were soaked overnight before sown. In part this was done because the seeds would swell and the ones that didn’t were likely to be unviable. However, we now know that soaking sweet peas overnight can harm the seeds, so it’s best to only soak for a couple of hours. I rarely bother soaking the seed, it’s too easy to forget to and I find that you get very respectable results without bothering. On the whole dark coloured sweet peas need soaking longer than light coloured varieties. However, the soil does need to be moist for germination so it makes sense to use a propagation cover or a clear plastic bag so that the compost doesn’t dry out.
Sweet peas hate having their roots constricted and for this reason many people use root trainers, which are long seedling pots that open by the side so as to minimise root disturbance. The other trick is to use empty loo roll holders which can be planted in the ground, where the cardboard will rot away. If you don’t have either of these to hand it’s better to plant two or three seeds in a 9cm pot, removing the weakest two, and avoid sowing in modules or seed trays because they are too shallow.
Sweet peas are often sold in mixed packets and this kind nearly always have erratic germination, so sow more than you need because some will never germinate. Once they are up it is very important that you move them to cooler conditions where growth will be slowed down. Grow them on a heated propagator or a warm window sill in late winter light levels and you will get very leggy plants.
If you find that your plants are growing leggy then just keep pinching them back. When the plants have two true leaves, these are adult leaves that appear after the seedling leaves, pinch out the top of the plant, using your thumb and fingers. Pinch out just above a set of leaves. This will cause the plant to bush out. You can do this two or three times if necessary.
Ideally sweet peas need to grow at 10 degrees Celsius until the threat of hard frost has passed, then they need to be hardened off for about two weeks in a cold frame or similarly protected space before they can be planted out in late April to May.
Sweet peas do best in organic rich soils that are well-drained. If you can dig in some homemade compost that will make a lot of difference. Slugs can be a real issue. Use beer traps, organic slug pellets and go hunting with a torch a night. Once the sweet peas are established slugs aren’t such a problem, but sometimes getting there can be a battle.
Sweet peas want to grow in the sun, their feet can be cooler, but they don’t tend to flower well if they are grown in shade. They will need something to climb up such as a tripod and will need tying in initially. Though after a while they start to produce many tendrils and will do the job themselves. The more you pick, the more flowers you will get for longer. Letting any flowers set seeds tells the plant that is job is almost done and flower production slows down considerably.
My favourite variety is the old fashioned Lathyrus odoratus ‘Matucana’ which has violet and deep purple blooms and the most heavenly scent. It’s an open pollinated variety so its easy to grow. You could even save your own seeds. If I can’t get hold of this, I go for a mix colours, choosing a packet that says they will be scented (not all are) and chance my luck that the colours look as good as they do on the packet. Pure white always looks very stylish and the very dark purples can be very dramatic.