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Growing Sweet peas – Indoors & outdoors
Last Updated on January 21, 2020 by John
Sweet peas are, as their name suggests, very sweet not only in production but in fragrance, however, it’s the annual varieties that are known for their amazing scent but you can also get perennials sweet peas that come back year after year but many of these are not that scented.
Thankfully growing them is quite simple and you can easily grow them from seed planting in autumn and overwintering in a cold greenhouse or cold frame or you can simply sow them in spring and not have to worry about overwintering but they may need hardening off first which usually just means putting them out during the day and bring them in at night for a week or two. Failing that most garden centres and nurseries sell them in 9cm pots but growing them from seed gives you the best choice of varieties.
Sweet peas can be planted in the ground, in pots and even in hanging basket trailing over.
How long do sweet peas take to germinate?
That depends on where you live, but on average between 7-15 days, so you don’t have to wait long, they germinate even quicker when placed in a heated propagator.
When do you plant sweet peas?
If you live in a warmer area with mild winters and want to try sowing them outdoors into the ground, you can sow the sweet peas in the fall. For any other area and for most of the UK, it is best to do it in spring around March to April.
If you want to sow them indoors which is often more successful, this can be done in October or November which may also lead to earlier blooms, young plants can then be overwintered in a cold frame or greenhouse.
The easiest time to sow them between January and April as you don’t need to overwinter them but you still need to harden them off first before planting out if there is still risk of frost.
Regardless of when you sow, you can also try soaking the seeds in water for an average of 9 hours beforehand so that the seed coat is softened and the sprouting process is expedited. Some gardeners recommend a few methods to help with germination but we have always had no issues with just planting the seeds straight away and have always had a good success rate.
Are sweet peas annuals or perennials?
Most sweet peas are considered annuals but you can find some perennials out there such as Lathyrus latifolius, however, they won’t have the sweet pea fragrance of the annuals. But they do grow year after years and still give a good show growing to over 6ft tall.
Perennial sweet peas can be planted as you would any perennial and can be put back for to ground level for winter.
Planting sweet peas
What you will need:
- Sweet pea seeds
- Potting soil (if you are growing in pots or germinating indoors)
- Fencing or support structures
Prepare the soil for the best show
When you are ready to plant your sweet peas in your garden, be aware of the fact that they eat a lot so you should apply a layer of bone meal, compost or manure, and natural fertilizer to the soil beforehand, we recommend doing this up to 2 weeks before planting if possible. Mix all of this in deeply to achieve optimum results.
The vines will grow rapidly and they need something against which to climb. To that end, you can place support posts or sturdy frames where you have your sweet peas and they will scramble up them as tall as 6ft.
When you sow seedlings, do so after the last frost, in rows. You want one row on either side of the trellis or structure you are using. Plant each seedling around 20cm apart. The vines will begin to explode with new, lush growth at which point you should tie them to the trellis so that the vines can be supported. You might see over 30cm of growth per week once they get going. It’s also a good idea to pinch the top out once they reach around 1ft tall as this encourages them to bush out more for an even better show.
Sowing Indoors before planting out
If you sow them indoors this can be done between January and March, fill a 9cm pot with quality compost and place around 6-7 seeds nicely spread with an inch of compost on top. Water well and cover with a piece of clear plastic such as a sheet of polythene.
Once they shoot, remove the plastic and once established enough plant out ensuring the risk of frost has passed or harden off by placing outside during the day and bring in at night to protect them from frost. After a couple of weeks, they should be fine to be planted outdoors.
Sweet pea care
Sweet peas are at risk for slugs and snails when they are developing younger growth, so keep a lookout. These plants are also susceptible to things like powdery mildew, leaf spot, and pythium root rot.
Do sweet peas need full sun?
Yes, sweet peas prefer full sun and will do best with full sun exposure.
As far as water is concerned, they love it. They need consistently moist soil, especially during warmer weather but it must be well-drained.
After they are successfully planted, you should feed them with a mixture of seaweed emulsion and diluted fish emulsion. Once they are flowering be sure to deadhead them regularly to encourage more flowers and remove seed pods straight away.