Sweet Peas - Sowing and Growing
How to Sow and Grow Lathyrus Odoratus for Scented, Colourful Flowers
Aug 7, 2009
Many gardeners opt to buy them as young plants via mail order or from garden centres in late winter or early spring, but sweet peas are easy to raise from seed - and the best time to do it is in the fall, or autumn.
Many experts advocate chipping or soaking the seeds before you sow. Why? Because some varieties have a thicker seed coat that doesn't absorb water as easily as others. It's generally thought that the darker-coloured seeds are the trouble makers that need treating before sowing - but should you chip or soak?
Sweet Pea Seeds
Chipping the seed coat involves rubbing, or nicking, a small section on the opposite side of the 'eye', from where the seed will grow. You can use a small piece of emery paper or a Stanley knife, but it's fiddly and time-consuming, and you'll end up with several seeds pinging off into the darker corners of the shed or greenhouse if you don't keep a firm grip!
Soaking is the easier option but you need to be careful as sweet pea seeds rot easily; if you're going to soak you should do it for up to four hours and no longer - certainly try to avoid leaving them in water overnight. Make sure the water is tepid and collect only those seeds that have swollen to about one and a half to two times their size. These will have absorbed water. Discard the rest.
When to Sow Sweet Peas?
Don't feel you have to chip or soak seeds, but however you treat them, you should sow sweet peas into a dryish seed compost, about 1in. (2.5cm) deep and water well. September and October are the best times for sowing if you live in the northern hemisphere (March and April in the southern hemisphere) as you end up with stronger plants that flower earlier and are able to ward off diseases better than plants sown outdoors in spring (fall/autumn sowings are made indoors, spring sowings outdoors).
Your seedlings are going to be in their pots for a good few months, so it’s important to give their roots plenty of room. You could sow several in a deep 3in. (7.5cm) pot or you could use Rootrainers, which are designed to accommodate one plant per cell – the inner walls are ribbed, which encourages roots to grow straight down rather than winding around. The other great thing about them is that when your plants are ready to go out the Rootrainers can be opened on a hinge and you can remove the sweet peas with minimum damage to the roots. Most garden centres and seed catalogues sell them.
Sweet Pea Aftercare
Once sown and watered, place in a propagator or seal the container inside a polythene bag and keep at 20-25°C (68-77F°) until after germination, which takes 7-21 days. Keep on the dry side and do not exclude light. Spring sowings can be sown outdoors, 1in. (2.5cm) deep in drills 3in. (7.5cm) apart.
Dig in plenty of organic matter during the winter months. As soon as seedlings are growing well it’s important to move them to a cooler location, such as a coldframe or unheated greenhouse, before planting out in spring when the ground has warmed, 9-12in. (23-30cm) apart. Pinch out the growing point once the first or second pair of leaves has opened. This will encourage them to branch out and produce more stems and therefore more flowers. If you want to grow for showing, you'll need to train plants as cordons, which involves training plants as one stem. In this case don't pinch them out.
Keep Sweet Pea Flowers Coming
Aside from boosting the soil's humus content by digging in plenty of home made compost, leafmould or rotted manure over the winter months, sweet peas aren't fussy plants. Watering with a phosphate-rich fertiliser (such as liquid tomato feed) once a week when the first flowers have opened will help encourage more buds but the best way to keep the flowers coming is to pick regularly. Even if you decide not to cut them for the vase it's important to dead-head on a regular basis or plants will think they've achieved their main objective of setting seed and will stop flowering.
Collect Sweet Pea Seeds
Of course, you can try to collect your own seed and sow it each autumn, but it's best to select just one plant for seed production and keep the others flowering. Allow insects to cross-pollinate and you could have some interesting results when your offspring flower next summer - after pollination the seed pods (which look like miniature pea pods) will swell. They will be ready for collecting when the pods begin to yellow - store them in paper bags, not plastic bags, and sow by the end of the year. Sweet pea seeds germinate best when fresh.
Support for Sweet Peas
Plants may need a little initial help climbing their supports (unless they're dwarf varieties that can be grown in baskets and tubs), but will soon be romping away. However, in hot, dry summers they usually become affected by powdery mildew - the leaves and stems look like they've been dusted with very fine talc! You can minimise this by mulching plants in early summer, to lock the moisture in, or by spraying with a fungicide as a preventive measure. Some gardeners even swear by cows' milk, which they spray on.
Plants are usually past their best by September and are certainly ready to be cut down by October at the latest. The lifted plants can be added to the compost heap.
Conclusion
Sweet peas are easy plants to raise from seed - even novice gardeners should get good results if they follow the tips above.
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