A job for autumn: Sow sweetpeas now for better blooms next year

RHS Botany for Gardeners

Sweetpeas have to be one of the highlights of summer. Their scent is like nothing else. Despite their delicate, spindly appearance, the seedlings are actually hardy little things. Which means they can be sown in autumn and grown on with minimal effort over winter, leading to earlier and often better and longer-lasting flowering the following summer.

Sowing and growing on sweetpeas is very easy, and the thought of  those seedlings merrily growing on through the cold winter months, ready to give tonnes of flowers next year, is a really cheering one as the gardening season starts to wind down and the days get shorter.

A bit about the sweetpea

The annual sweetpea’s latin name is Lathyrus odoratus. Lathyrus is its genus, of climbing herbs,
and odoratus its species, obviously referring to its distinctive scent. It is in the legume family (which includes peas and beans) which is presumably how it gets its common name; the plant looks a lot like a pea, and the flowers are sweet-smelling.

There is also a perennial form of the sweetpea, which is less commonly found so you are unlikely to get the wrong one by mistake, but if you find you have Lathyrus latifolius (everlasting sweetpea) you have the perennial version which is also lovely in its own right, but less suitable for sowing at this time of year.


How to autumn sow

This really is easy to do.

1. Chooose your sweetpea seeds. There are hundreds of varieties to choose from, offering different colours, size of flower, length of stem, flowering time but don’t let this put you off. Just choose the type you like the look of, all annual sweetpeas can be grown in this way.

2. (Optional) Alternatively if you grew sweetpeas this year, you can collect seeds very easily from the current crop and you should have a really good success rate sowing seeds you collect yourself if you sow them the same year, as they will be really fresh. To do this, just leave the plants after they flower until they form pods that look just like pea pods. They will be green and furry at first but will go brown in a week or so, and once they are totally brown and crispy the seeds are ready to collect. Just pull or cut the pod off, open it carefully and take the seeds out. They are easy to handle as they are quite large for the size of the plant. Don’t store them in plastic as there will be too much moisture and they will rot. Keep them in a paper bag or envelope until you’re ready to sow them.

2. (Optional) Soak your seeds in tepid water for a few hours. Sweet pea seeds have a hard outer layer and you can soften it to help aid germination. Some people also scratch the outer layer or chip part of it away with a knife. Personally I think this could do more harm than good if you’re not very careful- both to you and the seed! And I did say sweetpeas were easy to sow, to be honest you might well get a very good germination rate by missing out this stage altogether, especially if you buy one of the commonly sold sweetpea varieties from a large scale supplier, as a lot of modern popular varieties have been bred not to need this preparation before sowing.

Soak sweetpea seeds before sowing to soften the seed case

3. Choose your pots. Lots of seeds are started off in seed trays- shallow trays about 10cm deep- and then moved on once they have germinated. The process with sweetpeas is different. They quickly grow long, deep roots and they don’t like disturbance to their roots once they have started growing. Sowing them now means they won’t be planted out for up to 6 months, so they need to be sown in a container that can sustain them for that long. Your pots should be at least 20cm deep, and you’ll want to sow three or four seeds per pot.

4. Fill the pots with compost. Again, a lot of seeds are started in a specific seed compost which has a low level of nutrients because seedlings stay in it for a few weeks at the most. Your sweetpea seeds need to be sown in a different type of compost which will provide more nutrients; a regular multi-purpose compost will do the job well. Fill the pots to a couple of cm below the top and firm it down so it supports plants as they start to grow.

5. Poke small holes about 3 cm deep in your compost with something like the blunt end of a pencil. Pop the seed in and cover it over with compost.

6. Water the seeds gently, making sure not to wash them out of the compost. If you have a ‘rose’ head for your watering can, which is an attachment with lots of small holes in it, use that.

7. Place the pots on a sunny windowsill. They need some warmth to help them germinate. You should see small green shoots certainly within a week.

Sweet pea seedlings just after germination

8. Once the sweetpeas are about 20cm high, start to ‘harden them off’, which means getting them used to colder weather outdoors. Put them outside during the day and bring them in at night for about 5 days. After this you can leave them outside. They need a bit of protection from heavy rain and wind. Don’t let them get buried in snow, but don’t worry too much about the cold. Water them once a week. They can be planted out around April-May in most places.

Something to look forward to next year, right?


“Here are sweet-peas, on tip-toe for a flight:

With wings of gentle flush o’er delicate white,

And taper fingers catching at all things, 

To bind them all about with tiny rings.” John Keats


5 Comments Add yours

  1. Bec says:

    Thank you for this post – really helpful information. I’ve never grown sweetpeas from seed – I’ve been gifted them 🙂


  2. Bec says:

    But I love them in the garden – Spencer varieties been best for me in my soggy northfacing backgarden


    1. That’s a very useful tip Bec, thank you. I imagine they quite enjoy the cooler conditions of your garden.


      1. Bec says:

        Yes I think so – I’ve had no joy with dwarf varieties either


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