on growing sweet peas from seed

Who is not a fan of sweet peas? Before growing anything each year, there is the same ceremony. Raiding seed drawers, scrolling through social for saved plants or old pictures of gardens, garden designer plant lists or the occasional text to a friend to remind me of something they have grown - it does not get more complicated than that.

Laying everything out on the table and maybe an amateur drawing of the garden or a pot. It inevitably starts with Sweet Peas; they are fuss-free plants to grow, give lots of fragrant scents and fill in empty spaces fast.

The challenge is always; which colours you want to grow. Sweet peas come in many shades of white, pastels, purples, pinks and even orange. They are a go-to for pots or can be planted straight in the ground. Sweet peas are good for climbing up frames or even an arch, so you get surrounded by their scent and ideal for a supply of cut flowers for the house. Bear in mind that some sweet peas have a stronger fragrance than others so check the variety before you buy!

Since it is a garden staple, I have gathered all the growing info to get the most out of growing sweet peas.

Complete Sweet Pea Growing Guide

Soil, Sun and Season

Sweet peas generally like soil which drains well but holds some moisture. They also love the sun, so plant them in a position with direct sunlight.

For best results, sow sweet pea seeds (undercover) in late October/November or late February/March, as the temperature and light levels are low in the winter months. Then plant sprouts outside during a mild spell between March and May; once frosts have passed. Or you can sow directly in the ground in April or May.

Sowing and Planting

Sweet pea seeds germinate well, but you can give them a helping hand; before you start sowing, place the seeds on some damp kitchen paper for 24 hours; to soften their hard shell. Or you can nudge germination by nicking the seed coat with a knife, avoiding the ‘eye’ area. Sow seeds in good quality, peat-free compost and in pots which aren’t too shallow (or invest in root trainers or use old loo rolls) and give plenty of room for their roots to grow downwards and branch.

To sow, dampen the compost, put two seeds on top of the compost in each root trainer and then push the seeds about 2-3cm below the surface. Cover the hole with compost. Then leave to germinate outside undercover if sowing in autumn or spring. If you start in winter, give them gentle warmth on a windowsill to germinate.

Keep them cool (5C), and don’t water them until you see seedlings come through after about ten days. Keep an eye on them and water lightly whenever the soil looks dry.

After about three weeks, when there are three or four pairs of leaves, pinch out the tips of young sweet pea plants. You can do this by squeezing off the growing plant tip between your finger and thumb. Pinching out is very important as it will make the plant bushy.

Plant out sweet peas

When the roots have filled the root trainer, it’s time to move them into a larger container. Again, a deep pot is best - 1 litre with good compost and water them once re-potted. When the roots have filled the container, it’s time to plant them outside (between March and May, during a mild spell).

Before planting outside, you can harden your sweet peas by putting them out during the day and returning them to a frost-free place each night. 

It is also a good idea to enrich your soil when you plant your sweet peas, by adding manure or garden compost. Not only will this provide food for your sweet peas, but it will also help the soil hold moisture.

Caring for Sweet Peas

Watering

Sweet peas don’t like to dry out; water regularly and daily during a drought.

Fertilising

Start feeding sweet peas with a high potash fertiliser (such as tomato feed) when flower buds appear and every couple of weeks after that.

Staking

They will need vertical support or frame as they often reach over 1.8m tall! As the young sweet pea plants grow, tie them into vertical support. Tying up the stems creates healthier plants and will make them grow more quickly.

Deadheading

It is so vital to deadhead your sweet pea flowers. Cut off spent flowers at the base of the stem.

Seed Collecting

You can collect any seed pods you have at the end of the season, allow them to dry for a month or so and store them in an envelope.

Seasonal Sweet Pea Checklist

Sweet Pea SOS - Common Issues

My sweet peas are turning yellow!

Yellow leaves on sweet peas can be a sign of various fungal problems. Make sure the soil doesn’t get waterlogged and drains away well.

Why are my sweet peas are dying?

Sweet Peas are ravenous growers and want plenty of water, sunlight and feeding. Growing them up with vertical support also give them more access to sunlight and will help them thrive in your garden. 

My sweet peas will not flower.

Deadheading regularly encourages new blooms. Also, be sure the sweet peas are in full sun as they need plenty of sunlight to flower well.

What is the white dust on my sweet peas?

White dust on sweet peas is a sign of mildew. Mildew can be a problem for sweet peas, especially if they are under stress - drying out or not getting enough sun and fertiliser. You can also apply anti-fungal sprays every two weeks, or a homemade brew of chives water which is high in sulphur. 

The flowers on my sweet peas are all dropping off...

Sweet peas have a tendency to drop their flowers when the soil is very dry. Remove any seed pods that form which can sap the strength of the plant and then water very well (in the evenings). Digging in lots of compost before you start sowing will help with this.