A flower lover and seed merchant’s guide to different varieties of the sweet pea flower (latin name ‘Lathyrus odoratus’), & my best tips for growing sweet peas from seed.

Sweet peas are one of those magical flowers. The scent alone merits their inclusion in any garden, whatever size or inclination, and the fact that you can sow them in the darkest days of late winter makes them all the more special.

I’ve been growing these beautiful flowers for years, and sell the most exquisite varieties in my seed shop for Gather members. In fact, I love them so much that I have written a whole book about them (again, available inside the Gather library). 

I’ve learned a thing or two about successfully growing abundant sweet pea flowers from seed over the years as a flower grower and seed merchant, and in this blog post I’ll share some of my tried-and-tested tips for growing, as well as giving you an idea of some of the best varieties of sweet pea for cutting, colour, and fragrance.

Being a die-hard fan of the English cottage garden, I stock the loveliest, most scented and the most generous of the British sweet peas. They are so hard to find in America but the amazing news is that I have managed to stock all of my favourites in the Gather USA seed shop.

A few of my favourite varieties of sweet pea flowers

How long do sweet peas flower for, & What month do they flower in the UK & USA?

When sweet peas flower depends on when you planted them, and the weather of course, but generally peak sweet pea season in the UK is in June and July. If you keep cutting them little and often, watering well, and deadheading old blooms, sweet peas can flower all the way through the summer and as late as October.  In warmer parts of the USA they may well peak later in the season, September-October. But one of the (many) wonderful things about this flower is that you can plant them throughout the winter and spring so as to have abundant flowers through the summer and into the early autumn.

Do sweet peas come back every year?

Most of our familiar varieties of sweet pea flowers are annuals, meaning they don’t grow back after their first year, and others are perennials, which means that they can keep blooming year after year.

The annual varieties tend to be highly fragrant and the vines tall and packed with flowers, and the perennials don’t tend to have a scent; if you want fragrant and abundant sweet pea blooms, taking the time to plant new annuals from seed each year is well worth the effort. The seeds I sell in my Gather shop (available to members in the UK and USA) are annual, but it is so incredibly easy to save their seeds to plant again from your own crop the following year if you don’t want to buy new seeds every year. Time it right, and you will have sweet peas in your garden forever…

When to plant sweet peas

I suggest sowing a few sweet pea seeds of each colour in October, a few more at Christmas, and then one last sowing in the spring. It is good to have spares in case of mice and staggering sowing means you get a much longer flowering period than if you sowed everything at once.

Plant seedlings out after the last frost, roughly 8 inches apart, against a support, trellis or netting.  Tie them in to get them started. 

How to grow sweet peas

To sow your sweet pea seeds, you will need:

·    Peat-free compost. Not the seed compost, a good multi-purpose.

·    Cardboard inners (toilet rolls work) or, if you are going to reuse, good quality plastic root trainers.

·    A container to hold the inners, one of those plastic trays that mushrooms come in is perfect

·    Labels

·    Seed

There is also a bit of a debate about pre-soaking seeds before sowing and, like so many of these gardening dichotomies, it inspires strong feelings in some. Not in me, I hold a pragmatic view. If the seed is over a year old and looks a bit wrinkled, soak it. If they are plump and look smooth and round, they probably don’t need it. The initial watering will suffice.

Fill your pots with good quality compost. Sweet peas produce tap roots, so they do need a bit of depth underneath them. This is why cardboard tubes or root trainers are better than small pots, but the deeper 9cm pots can be used if that is what you have. 

I always used to say sow two seeds per tube because most sweet peas germinate at around 65%. However, my seed has proven to be so good, I think I am going to say one seed for each tube. Sweet peas do like space and I am never going to thin out a perfectly healthy sweet pea seedling. I am just not that person. 

How deep to plant sweet pea seeds

It is important to make sure the seed is not buried too deep. You are aiming for about a centimetre. I find dibbing with a pencil and dropping the seed in is incredibly satisfying, but it is hard to keep track of the depth and everything sinks again when you water. Filling with compost to very nearly the top and then adding the seed and covering is safer in terms of knowing how deep they are, but also doesn’t compact the compost. 

Water very gently but very thoroughly. When I say gently, the water will bounce out of the container and splash everywhere, particularly when the compost is dry. Do it in a sink or outside. I haven’t found a way of doing this without water spurting off in strange directions so I just accept that it will and take precautions. The first water should be quite a comprehensive one as it takes the place of the soaking step that we have missed out (if you have) and there needs to be enough moisture in the compost to soften the seed coating. 

The mantra to remember for most seeds, but particularly sweet peas, is warm and dark for germination, cool and light for growing on. Around 15 degrees Celsius is about right according to the experts but I think a kitchen windowsill, or any place out of a draft indoors, is fine.  

One of the most important reasons for doing this indoors is that (hopefully) you don’t have mice inside the house and mice love sweet pea seeds. They will generally ignore plants so once they are up and growing, they are fine. 

Keep them moist but not wet. Once the shoots are up and through, get them out in the cold. If you molly coddle them, you get weak, leggy plants. 

How and when to pinch out sweet peas

Once the plants are 4–6 inches tall, pinch out the central growing tip, just above a leaf joint, leaving just two or three leaf nodes. This will encourage the plant to branch vigorously from the base. If they are growing really well, it might be worth putting the individual tubes into a pot.

Hardening off sweet peas

If you followed the instructions above and turfed your precious plants out into somewhere cold, you shouldn’t need to harden them off. They really are tougher than you think. If you (like me) couldn’t quite bring yourself to expose them to the elements and they have been sitting in a sheltered greenhouse for the winter months, you are going to have to be brave and harden them off. This just means putting them out on warmer days and taking them in at night for a week, and then putting them out on the warmer nights and taking them in if frost is forecast.

After a fortnight of this ridiculous juggling, they will be fine to be out in all weathers.

Sweet peas are surprisingly hardy so, although the advice is generally to wait until the last frost, it doesn’t matter if you time this a bit wrong. Obviously wait for the soil to start warming. A fresh rash of weed growth is usually the sign to put plants in the ground.

Sweet peas are heavy feeders and require a little extra pampering to produce abundantly. Prepare planting beds by applying bone meal, a thick layer of compost or well rotted manure and a generous dose of natural fertiliser. They grow rapidly and require a strong structure to climb. Hazel teepees are perfect.

Sweet peas love water, and without consistent moisture they will fail to thrive. Keeping their thirst quenched during warm weather is crucial. Feed plants weekly with diluted seaweed emulsion.

Growing sweet peas in pots

If you are thinking about growing in pots, I’ll warn you now; you need big, deep pots. At the very least, 45cm in diameter. 

All peas have long tap roots, and all peas are hungry plants, so I wince when I see five sweet pea plants crushed into one small pot, usually accompanied by shiny bamboo canes that the tendrils keep slipping down. You might get the odd flower from them, but they will never live a happy life, and my heart will break.

My pot is an old metal wash tub from the tip shop and it is at least a metre tall. This is no time for terracotta. Fill it with the best peat-free compost you can get your hands on and be prepared to feed. Bear in mind that if you’re severely limited on space you can buy specially bred dwarf varieties of sweet pea flowers.

Cutting sweet peas

Once flowering, you can cut sweet peas little and often and they should keep blooming through to the end of the summer.

11 of the best varieties of sweet pea flowers for fragrance, cutting, and colour

‘Indigo King’ sweet pea flower

A dramatic sweet pea in rich, royal colours.

This is a dramatic sweet pea flower in rich, royal colours. I have been utterly seduced by the intensity of the colour of Indigo King, one of the most fragrant sweet pea varieties. Deep, rich purple standard petals are set off by vibrant violet wings. This sweet pea is incredible for scent and blooms with abundance, even in the heat. 

Sow indoors in autumn or winter, direct in the ground in spring. You can start cutting the flowers in late spring and just keep cutting until late autumn when the last blooms appear.

’Piggy Sue’ sweet pea flower

Soft blush pink edges on parchment ground.

Rivalling the tulip mania of 1634, the demand for this exquisite sweet pea is a result of its incredible beauty. Perfect tones of vintage blush, if I could only grow one sweet pea, it would be Piggy Sue.

‘Nimbus’ sweet pea flower

Inky, purple-grey streaked blooms.

The most intricate and the most beautiful, Nimbus has dark streaks and edges on a cream ground. Famed for a long stem and an even longer vase life.

‘Charlie’s Angel’ sweet pea flower

Romantically soft powder blue.

Generally accepted as one of the best sweet peas for cutting. Long stems, big flowers, great scent, good vase life.

’Zorija Rose’ sweet pea flower

Eye-catching deep magenta pink blooms.

Arresting. Striking. Stunning. Undeniably pink. I am not going to pretend Zorija Rose is subtle but she is assertively, unapologetically herself. And what’s not to love about that?

’Bristol’ sweet pea flower

Soft blue with waved cream edges.

Highly scented variety with large flowers on strong stems.

‘Jilly’ sweet pea flower

Big, beautiful creamy blooms.

My favourite. Softly coloured and elegant in form. They open in cream and then lighten to ivory.

’Mollie Rilstone’ sweet pea flower

Cream edged with soft apricot-pink

A classic, and for a reason. Mollie is unapologetically romantic. Starts as an edged bloom, then fades to a perfect vintage cream. An utterly perfect sweet pea.

‘Erewhon’ sweet pea flower

A super-stylish bi-colour dark lavender and strong pink.

If I hadn’t already committed to Jilly as my favourite, Erewhon would be it. It is rich but delicate, strong but sophisticated, she is an absolute cracker.

’Cream eggs’ sweet pea flower

Utterly unique; prolific cream with a blue wire rim.

Super-charged with scent but that’s not even the special thing about this beauty. It’s the colour. Big cream flowers with a light blue wire rim that darkens with age.

All of these varieties of sweet pea flower seeds are available to purchase inside the Gather seed shop. The seed shop is exclusive to members of my online space for flower lovers, Gather.

Membership costs £10 a month (the price of a few cups of fancy coffee), and yes, you can join for one month just to get seeds if you want—cancelling is hassle-free and you can do it any time. Seeds are available in the UK and USA.

Gather membership also gives you access to a whole library of inspiring flower growing guides and interviews with flower experts. I’ve been told that Gather is “a peaceful respite in the noise of the everyday”. You can find out more this way.

And, if you’d like to get your hands on my top tips for successful seed-sowing, sign up to my newsletter below, and I’ll send you my free guide to growing flowers from seed. See you in your inbox soon, and I wish you an abundance of flowers this summer…