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Grow at Home: the best way to grow Sweet Peas

Written by Sarah Talbot

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Posted on 18 January 2021

Sweet peas are gorgeous fragrant climbing plants that are great as cut flowers and a treat for the pollinators on your plot.  They grow well in the garden or in pots if you don't have much space.  

Which to choose

Some sweet peas are annuals (last just one season) and some are perennials meaning that they will come back year after year. 

blue sweet peas grown in Haxnicks Rootrainers

So that is your first choice - are you happy to replant each year?  The pay off if you do is that the annuals are nearly all beautifully scented.  There are a couple of scented perennials - Lathyrus nervosus, Lord Anson's Pea, and Lathyrus pubescens but generally you will sacrifice the delicious scent if you go for perennials.

Your second choice is colour.  There are many gorgeous mixed seeds available  for the country garden feel.  Or you can get a big range of single colours if you have an area you want to be in a specific colour.  

Lastly, its about where you want them to grow.  Most are climbers so need support - we have some great ideas for this further down.  But there are also dwarf varieties and clumping varieties that don't need the support.    

Sowing 

Sow annual sweet peas in either October to November to get nice early blooms the next Spring.  Or from mid January to April.  

The seeds have a hard seed coat and people disagree on whether they germinate easily.  There are ways to aid germination so try them and see what works for you. Options include

- plant them straight out of the packet (see how below)

 - place your seeds on a layer of moist vermiculite or kitchen tissue in an airtight container in a warm room.  Sow them as soon as they swell or begin to sprout.

- soak the seeds overnight - they then need to be sowed immediately or they can rot. 

- nick the seed with a sharp knife avoiding the 'eye' (small, round mark) then plant

Sweet peas in Haxnicks Rootrainers

However you do, or don't, treat your seeds, Sweet Peas have long roots and dislike root disturbance so by far the best way to grow them is in Deep Rootrainers. You can sow them direct into the ground but it will be less successful.

Fill the Rootrainers with good quality, peat-free compost and add 1 or 2 seeds per cell. Cover with 1cm (1/2") compost or vermiculite.  Water well, cover with the lid provided and place in a cold frame or greenhouse.

If you are planting in Autumn/ Winter then ensure that you have somewhere where they can grow protected from the frost until spring.

Pinch out the tips of the plants when they have 4 sets of real leaves and reach about 8-10cm (3-4") tall.  This will encourage bushy growth.

Planting Out

Once all risk of frost has passed you can plant out your sweet peas.  This is usually mid to late May depending where you are.  They need to be hardened off for a week or two before you plant them out.  Do this by putting them out in the day and taking them back in to a frost-free place at night.

Sweet pea seedlings showing roots as grown in Haxnicks Rootrainers

If you have 2 or 3 per cell then don't worry about separating them.  They can be planted together.  However, if you have bought them from a garden centre you may find 10 plants per pot.  If this is the case then it is best to tease them apart a little and plant in 2s or 3s.  

About a month before planting make sure the soil is good by adding some compost or well rotten manure and digging it in before planting.  Then plant them 5-8cm (2-3") from your supports and water them very well.  They will need tying in for the first 5 or 6 weeks.  After that most varieties will have grabbed your support and be away.  

Continue to water well to get them fully established.  

Supports

Most sweet peas will grow to about 2m in height so support is essential. 

They can climb up natural supports like trees and can vastly improve ugly fences. But many gardeners simply make a wigwam of bamboo canes for them to climb up.  If you would like to do this then Cane Rings are the ideal thing to help keep your canes in place. 

Another way to support them is with a Garden Maypole.  You can grow your own living maypole on your plot! 

 If you really want to make a statement then how about an architectural frame?  You could mix sweet peas with veg such as beans, peas, pumpkins, etc. and be the envy of your neighbours! We have a choice Big Ben, Eiffel Tower or London Eye
Haxnicks Plant supports - Cane Rings, Garden Maypole, Big Ben best for climbers and sweet peas

After Care

A soon as they start flowering start feeding with a high potash fertiliser, such as tomato food. Pick regularly to encourage more flowers and prevent them from setting seed. If you do this they can last all the way through to September.   

Continue to water any growing in pots, and both pots and garden grown during very dry weather.  If you notice flowers dropping this is a sign that the plants need more water.  In particularly dry years add a 10cm mulch of organic matter to the entire root area and water well.

After Flowering

If you are growing perennial sweet peas then you can either cut them back to ground level in autumn or leave them in place over winter to provide a habitat for wildlife. Then cut them back to ground level in February.

For annuals, in September collect the seeds (pods will be dried and papery looking), dry and store in a paper bag for next year.  Then pull out and compost the plants or leave as a habitat if you don't mind looking at them.

Pests & Diseases

Young plants are attractive to slugs & snails.  you can combat this by making sure the soil is warm enough when you plant for the young plants to establish and grow quickly.  

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