Expert Lathyrus Growers Share Sweet Peas Growing Tips Learnt Over Many Decades
Elizabeth is a Permaculture Garden Designer, Sustainability Consultant and Professional Writer, working as an advocate for positive change. She graduated from the University of St. Andrews with an MA in English and Philosophy and obtained a Diploma in Applied Permaculture Design from the Permaculture Association.
Reviewed By COLIN SKELLY
Colin is a Horticulturist and Horticultural Consultant with experience in a range of practical and managerial roles across heritage, commercial and public horticulture. He holds the Royal Horticultural Society’s Master of Horticulture award and has a particular interest in horticultural ecology and naturalistic planting for habitat and climate resilience.
Contributions From CAROLE TATE
Carole is the General Secretary of The National Sweet Pea Society, based in Buckinghamshire. Carole has created displays for the RHS as well as local shows, where she has won several accolades.
Phillip has 40 years of experience growing these wonderful annuals. He has bred Sweet Peas that have been awarded the RHS Award of Garden Merit and also won numerous awards at flower shows.
Georgina grew up in the UK surrounded by sweet peas that her grandmother grew. Ever since she was young, she had a passion for gardening and, after moving to the USA, is now the owner of Sweet Pea Gardens, a venture she started in 2018.
Emily is a Gardening Writer, Photographer and Videographer from Derbyshire, UK. She is the Founder of Emily's Green Diary - a community of more than 75,000 people who share in her gardening journey.
Sally Flatman is the host and creator of the 'Our Plant Stories' podcast. She is a former BBC Radio producer and has received an RHS Level 2 Certificate in the Principles of Horticulture from Capel Manor College.
IN THIS GUIDE
Sweet peas are without a doubt one of the most popular annual flowers grown in the UK.
Beautiful, fragrant and useful, there are many reasons to grow them, or a perennial type, in your garden.
We interviewed three expert growers of these plants especially for this guide:
- Carole Tate – The General Secretary of The National Sweet Pea Society.
- Phillip Kerton – Owner of Kerton Sweet Peas.
- Georgina – Owner of Sweet Pea Gardens.
When questioned, Phillip cites the “range of colours and scent” as his reason for being so passionate about growing Sweet Peas, whilst Georgia puts it down to the plant’s “nostalgia, fragrance and pure prettiness.”
These climbing plants are rightfully popular for their delicate pea flowers in a range of hues, and for their pleasing fragrance.
As legumes, these plants can also be useful for their ability to co-operate with bacteria in their roots, which are able to take atmospheric nitrogen and make it available in the soil.
Nitrogen is a key plant nutrient, so this is good news for plants placed in the spot after sweet peas, or, potentially, also for plants growing close by.
These flowering plants are also great for bees and other pollinators, and can help with attracting other beneficial insect life to your garden.
Overview
| Botanical Name | Lathyrus |
| Common Name(s) | Sweet Peas |
| Plant Type | Annual / Perennial / Climber |
| Native Area | Europe – Cultivated |
| Hardiness Rating | H3 |
| Foliage | Pea-like, deciduous |
| Flowers | Numerous hues |
| Flowering Months | June – October |
| When To Prune | February |
Sunlight
Preferred
Full Sun / Part Shade
Exposure
Exposed or Sheltered
Size
Height
1 – 2.5M
Spread
0.1 – 0.5M
Soil
Preferred
Loam, Sandy
Moisture
Well drained
pH
Any
There are two main types of sweet pea, the common annual type and perennials.
Annual sweet peas, Lathyrus odoratus, as gardeners know them today, were cross-bred and cultivated by Scottish plantsman Henry Eckford in the late 19th and early 20th Century.1Don, M. (1999, June 13). Sweet smell of excess. The Guardian. Retrieved March 21, 2023, from https://www.theguardian.com/lifeandstyle/1999/jun/13/gardens
Bred from plants with purple flowers, in the wild, sweet peas are now available in a wide range of hues.
While these are the sweet peas best known to most gardeners, there are also perennial types, often known as ‘everlasting peas’.
These include cultivars of Lathyrus latifolius, L. grandiflorus, L. aureus, L. vernus, L. rotundifolius and L. nervosus, for example.
Though these are not fragrant like the annual types, they will return year after year, bringing many benefits to your garden.
Annual Or Perennial?
The first decision you will have to make when growing sweet peas is whether the annual or perennial types are best for you.
Annual sweet peas are an excellent choice for novice gardeners, and for sowing with kids.
They can be a great choice for inclusion among the crops in an annual kitchen garden, for growing in pots or containers, or for a sunny mixed border.
There are over 50 cultivars of annual sweet pea which have been awarded with an RHS AGM.
Just a handful of the great options to consider include:
- L. odoratus ‘Bobby’s Girl’ (pink)
- L. odoratus ‘Charlie’s Angel’ (purple)
- L. odoratus ‘Gwendoline’ (pink)
- L. odoratus ‘King Edward VII’ (red)
- L. ororatus ‘Mrs Bernard Jones’ (pink)
- L. odoratus ‘Blue Shift’ (purple and blue)
“I love ‘Mrs Bernard Jones’ for the copious amounts of sugar pink ruffled flowers and sweet scent,” explains Georgina.
“Another favourite of mine is ‘Blue Shift’. It is a fascinating variety that changes colour as it ages.
“The flowers start out a purple colour and slowly morph into the most wonderful turquoise hues.”
Perennial peas or everlasting peas do not need to be sown anew each year.
As perennials, they can remain in your garden over a number of years.
They can be a great choice for the sunny fringes of a forest garden or fruit tree guild, or for a herbaceous border.
Some great perennial types to consider include:
- L. grandiflorus (deep pink, AGM).
- L. latifolius ‘White Pearl’ (white, AGM).
- L. latifolius ‘Rosa Pearl’ (pale pink, AGM).
- L. rotundifolius (deep pink/red, AGM).
- L. vernus ‘Alboroseus’ (pink and white, AGM).
Sowing Guidelines
Sweet peas, both annual and perennial, are typically sown either in spring, between March and May, or in autumn, in October or November.
“I sow two batches of Sweet peas for my garden, one in October and the other in February, both under glass,” shares Horticultural Consultant Colin Skelly.
“This provides both some degree of insurance that at least one batch will be successful and two waves of flowers if both succeed.”
Sweet peas are particularly easy to grow from seed, even for beginners, so it is unlikely that you will need to buy plants.
However, if you wish to avoid this step you can also purchase plug plants in the spring.
Germination rates are usually excellent, though you can help ensure germination by carefully nicking each seed with a knife, avoiding the ‘eye’ area – this is not usually required.
Seeds can be sown in small, individual pots (3 seeds per 9cm pot), in soil blocks, or in seed trays – in good quality, seed-starting peat-free compost.
Growing your seeds in cooler temperatures might also improve their success rate, Phillip explains: “When the seeds have germinated, grow them in cooler conditions. This will stop the plants from growing leggy.”
“Sweet peas are hardy annuals and will withstand frost and snow,” advises Carol.
“They sulk a bit but do not die. Mine are outside hardening off in March and I plant out in April (in Lancashire).
“They can be planted earlier further south in the country, and usually May in Scotland (there is no point planting earlier as the soil is not warm enough and they will just sit until it warms up).”
“Grow sweet peas close to a garden bench so you can sit and enjoy their colour and fragrance,” Georgina recommends.
If you sow them in autumn, a frost-free place to keep them over the winter months is therefore preferred but not always essential.
When & How To Plant Sweet Peas
Indoors sown sweet peas should be hardened off before you place them outside.
This simply means slowly acclimatising the young plants to outdoor growing conditions.
Where To Plant
Sweet peas can work well in a range of settings.
Annual types can work well, as mentioned above, in a kitchen garden as a companion plant for annual crops.
Perennial types work well in borders or the fringes of other polyculture planting schemes.
Phillip from Kerton Sweet Peas suggests tilling your soil and removing any weeds before you plant out your Lathyrus in the chosen location for the best results.
Both types can also be grown in containers.
Spacing & Depth
Plugs or pots (with three seedlings in each) should be spaced around 20cm apart, through precise spacing is not hugely important and you do not need to worry about too much about separating the individual plants from one another.
Plant them to the same depth that they were in their previous container.
Caring For Lathyrus
Most sweet peas are not only incredibly easy to grow, but also very easy and straightforward to care for over time.
Supports
Most sweet peas require some form of support, whether that is other plants, a trellis or other support structure.
Make sure you choose a support tall enough to support the particular variety or varieties that you wish to grow.
But remember that you might be able to use natural or reclaimed materials and do not need to buy anything new.
Most sweet peas are self-clinging climbers, which have tendrils which latch onto supports.
However, there are some sweet peas that will need to be tied into support structures.
Some perennial types have a different growth habit and don’t need support at all.
Preferred Sunlight
All sweet peas can cope with a little light shade, but most will do best in an open position in full sun.
“I’ve always tried to grow sweet peas in my garden, but I’ve finally given up as they just don’t grow in my fully shaded garden,” shares the creator of Our Plant Stories Sally Flatman.
Soil Requirements
Sweet peas need a moisture retentive yet free draining soil or potting mix.
They will thrive in loam or sand but can cope with a range of soil types and are unfussy about pH.
They will not particularly like a heavy soil, and can rot in very heavy and very wet conditions, and a very dry and low-nutrient soil can also increase the chances of issues like powdery mildew setting in.
But in most situations, sweet peas will remain largely hassle-free.
Watering
“Water, water, and water again to ensure your sweet peas do not dry out but make sure they are not waterlogged: free drainage is essential,” says Carole.
Continue to water regularly when growing in pots or containers, through additional watering will only be required during very dry periods when sweet peas are growing in the ground.
Temperature & Humidity
Annual sweet peas are typically H3 hardy, meaning that they are hardy only in mild and coastal areas of the UK (down to -5 to 1°C.).
They will however, thrive in the temperatures afforded in most UK gardens during the summer months.
Fertilising
Especially with annual sweet peas, it is a good idea to feed plants with an organic, potassium-rich plant feed once a week or so after the flowers begin to form, to promote strong and healthy flowering.
This is especially beneficial when plants are growing in less fertile, lighter soils, or in pots.
Perennial types can benefit from a mulch (such as comfrey leaves) around the base, though take care not to mound mulch around the stems.
Dividing
Larger, mature perennial peas can often be divided in spring or autumn, and the divisions can be carefully moved to new locations in your garden.
Pinching Out
When annual sweet pea plants sown in spring are around 10cm tall, you should pinch off the growing tips to encourage bushier growth.
Autumn sown plants will usually branch naturally on their own.
Pruning
If you want the best blooms with long, straight stems, growing annual sweet peas as cordons will offer the best results.
Select the strongest shoot and train it up a cane or tall stake, and pinch out all the other side shoots and tendrils when they appear.
Perennial peas can be cut back to the ground in the autumn.
But for the sake of garden wildlife, it is best to wait until February before perennials are cut back.
The dead foliage and stems leave shelter for a range of creatures.
Picking Flowers
Sweet peas make great cut flowers.
Flowers should be picked frequently, as this will encourage more to form and prolong the flowering season, Carole explains.
“If they go to seed, they will stop flowering.”
Common Pests & Diseases
“If planted too close together, Sweet Peas can suffer from mildew and can also attract greenflies,” Carole from the National Sweet Pea Society explains.
“I leave the greenflies on my sweet peas and let the ladybirds sort them out.”
Sweet peas are not generally very difficult to grow successfully, but they can be very prone to slug damage, especially when young.
“I surround my sweet pea beds with hosta leaves to divert any slugs and snails,” says Carole.
Aphids can also be a problem for young plants.
Powdery mildew can set in, especially if plants are under-watered.
Viruses can also attack sweet peas, though this is not particularly common.
Saving Lathyrus Seeds
If you are growing annual sweet peas, saving the seeds is a good way to make sure you do not have to buy more seeds to enjoy these plants in your garden again the following year.
Simply leave seed pods on the plants until they get dry and papery, then collect them on a dry day in autumn, shell them from the pods, and store them in a paper bag in a dry spot until you are ready to use them.
