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Growing Sweet Peas - planting, growing and caring for them

Growing Sweet Peas - planting, growing and caring for them

14 minute read

Two Wests & Elliott's Gardening Guide To Growing Sweet Peas

When you consider growing sweet peas you need to decide between the two main types – there are annual sweet peas and there are perennial or ‘everlasting’ sweet peas, here are the basic differences:

Annual Sweet Peas – Lathyrus odoratus, being an annual these last for one season and so will need to be grown every year. These are the sweet peas we normally think of, they are the highly scented climbers

Perennial Sweet Peas – Lathyrus latifolius, being a perennial these come back every year, some are bushy and some are climbers but most have little or no scent.

You will find around 160 different species of sweet pea around the world currently, whilst sweet pea breeders are continuing to work on new varieties to introduce new colours, blooms per stem, etc.

In this post we are going to talk about growing annual sweet peas, so the information and advice you see below will be geared to you growing annual sweet peas.  

Growing Sweet Peas

When Growing Sweet Peas From Seed Which Varieties To Try
With so many different varieties of sweet peas to choose from, consider the height of the plants, the colour of the flowers and their scent when making your choice. Here are just a few examples you could try: 

  • Sweet Pea Matucana – grows up to 180cm in height, has stricking bicolour flowers of crimson and violet, an heirloom Graniflora type
  • Sweet Pea Bobby's Girl - grows up to 180cm in height, has pastel petals of cream with shades of salmon-pink towards the outer edges, a highly scented Spencer type
  • Sweet Pea Lavender Sprite – a compact plant growing to 25cm in height and a spreading habit (making it ideal for hanging baskets), has large, ruffled, light lavender coloured flowers
  • Sweet Pea Mrs Bernard Jones – grows up to 220cm in height, has very large blooms of almond-pink on white, introduced in 1980 by breeder Bernard Jones and named after his wife.

Sweet pea seeds are fairly large, making them easy to handle which makes them easy to sow and space out. They have a very hard shell, so although you can plant the seeds straight into the compost and they will germinate, there are a few methods which more experienced gardeners will use to increase germination success. These methods are fairly easy, so worth trying, even if it is the first time you are growing sweet peas from seed. 

First, you can try soaking the seeds pre planting, with the aim of softening the seed coat, which should make sproutng easier and faster. They can be soaked in tepid water from just a few hours or overnight and should be patted dry on a paper towel prior to planting. As they soak up the water they will swell and should be planted straight away after soaking - so don't soak, dry and then leave the seeds a few days prior to planting. 

Another option to try with sweet pea seeds prior to sowing is to 'chip' them - 'chipping' the seeds means removing a small part of the hard outer shell of the seed. This can be done with a pruning knife, nail scissors, coarse sand paper and should be done on the side of the seed opposite the eye. 

Growing Sweet Peas Under Cover / Indoors 
Now you have prepared your sweet pea seeds, you can decide what to sow them in. Using a general, multi-purpose compost, these seeds can be sown in standard seed trays, plant pots or specially developed deep cells which prodive lots of space for root growth. We will give you a brief idea of all three methods and you can decide which will best suit your time and space available. 

Growing Sweet Peas In Deep Cells
One of the most important things to know about sweet peas is that they produce long, tap roots as soon as germination takes place, so ideally you need to sow them in a container which is going to provide sufficient depth for these roots to reach deep into the compost. 

Sweet peas also don’t like root disturbance, so are best sown in individual cells where they can grow undisturbed without their roots becoming entangled with their neighbours.

growing sweet peas in rootrainers

This makes growing sweet peas in deep cell systems ideal, such as the traditional Rootrainers or the new Deep Root Plant Cells. Either of these will provide sufficient depth for healthy, strong root growth. Both systems also use hinged cells which are easy to open to inspect root growth and at the same time make it simple to remove plants ready they are ready to be transplanted.

Growing Sweet Peas In Plastic Pots
From the information above we know that you will need pots which are deep enough for the sweet pea roots, so ideally you are looking for pots which are at least 3½ inch (9cm) deep, whilst Monty Don recommends using pots at least 5 inch (12cm) deep.

Even though you are planting multiple seeds into one pot, to reduce the opportunity for the roots to become densely entangled you should only plant two or possibly three seeds per pot, placing them as far apart as possible.

growing sweet peas

Transplanting Your Growing Sweet Peas Outdoors 
When you have raised your sweet peas indoors – in your home, greenhouse or polytunnel – they will need to be hardened off prior to being planting into your garden. This should take up to 14 days so they can acclimatise to the colder outdoor temperatures without being damaged.

Sweet peas are greedy plants and will need nutrient rich soil if they are to flourish. So, if you are preparing a space at your allotment or in your kitchen garden for a long row of sweet peas then 4-6 weeks before you intend to transplant your sweet peas outdoors you should prepare the ground. Dig a trench and fill with well-totted manure or compost, you can even top up the nutrients in the ground with a sprinkling of a general-purpose fertiliser if you wish.

As well as the ground they are growing in being full of nutrients, sweet peas will do best when grown in a soil with good drainage but is also moisture retentive.

Ideally your sweet peas should be planted into a location in your garden which will get full sun – these are sun-loving plants that will produce more blooms when they receive plenty of sunshine. A partially shaded location will suffice if that’s the only space you have available.

Another important consideration when transplanting your sweet peas outdoors is that they need to be spaced sufficiently apart from each other – sweet peas are a plant which are susceptible to mildew so need good airflow around them. So ideally you should be planting them between 8 to 12 inches apart (20 to 30cm). This also means that if you are growing sweet peas in pots, the pots should be at least 12 inch (40cm) in diameter and the same in depth.   

Caring For Your Growing Sweet Peas

Depending on which variety of sweet pea you have chosen to grow, you are likely to need some type of support structure for your plants to grow up as they are prolific climbers. In fact, some sweet pea growers say that you can expect established plants to put on 1ft (30cm) of growth every week.

So, prior to transplanting your sweet peas outdoors, get their support structure in place and build it so that it is tall enough to hold the expected height of the plants when fully grown.

As they grow so quickly, you will need to stay on top of tying your plants to the supports as you need to – although most varieties of sweet peas have tendrils which enable them to cling onto their support, some will need your intervention with string or other ties to keep them upright.

We have lots of different ties and supports available so click here to take a look.

growing sweet peas up a support frame

Here are little tendrils
Helping them ready to climb.
Here are the sweetest colours;
Fragrance very sweet;
Here are silky pods of peas
Not for us to eat!

From ‘The Song of the Sweet Pea Fairies’ by Cecily Mary Barker.

Growing Sweet Peas In Your Garden Will Attract Beneficial Visitors
We might find the colours of sweet peas captivating and the fragrance sublime, but there are also insects which will be attracted to them, and which will benefit your garden, including:

Bees, honeybees and bumblebees – the fragrant, pastel flowers of sweet peas will attract these into your garden where they will go on to pollinate your other plants.

Butterflies – not only attractive to see in your garden, butterflies are also good pollinators as they flit from plant to plant.

Pests Attracted To Growing Sweet Peas
Sweet peas can be susceptible to a range of different pests and diseases, from when they are young plants in your greenhouse through to when they are tall, strong plants in your garden. Here are some of the common pests you could face: 

Aphids – these sap sucking insects can cause real problems for your sweet pea plants, where they will happily feed on the leaves, stems and flowers which results in damage and nutrient loss resulting in weakened plants that can be stunted in growth or distorted. A natural way to help keep aphids under control is to encourage beneficial insects into your garden - such as ladybirds and hoverflies. You will also find some garden birds, such as blue tits and long-tailed tits, will feed on aphids too.  

Spider Mites – one of the most common garden pests, these mites are smaller than the size of a pin head, yet can cause destruction to plants, especially those in greenhouses. Spider mites pierce the leaves of plants to suck up the plants' fluids and can result in the leaves changing colour, curling and eventually falling off. Spider mites are fast breeders and as a result this makes them hard to get rid of - you can use natural predators to help you such as ladybirds and lacewings and also ensure plants remain well watered - plants which are dehydrated are more susceptible to mites.  

Thrips – another sap-sucking insect, thrips will not only feed on your plants and weaken them, they will also transmit plant viruses from one plant to another (as will aphids and spider mites). This act of transmitting plant diseases can be just as devastating to plants, if not more so, than the physical damage they can do. 

Slugs & Snails – unfortunately young sweet pea plants seem to attract slugs and snails. It's usually a case of physically removing them by hand or you could try companion planting, using strongly scented plants to discourage them or growing 'sacrificial' plants for the slugs and snails to munch on instead of your precious sweet peas.    

Diseases Affecting Growing Sweet Peas
Like other plants, many of the diseases which sweet peas can suffer from result from overcrowding or over-watering, with likely problems including: 

Powdery Mildew – when you research sweet peas and diseases, the general consensus is that at some point in their life sweet peas will be affected by powdery mildew, especially towards the end of the flowering season - if it is after they have bloomed, then at least you have been able to enjoy their fragrance and beauty! There are a few ways to reduce mildew attacks. Firstly ensure they are planted in a rich, moisture retentive soil, and r water regularly, so that they don't become over dry. When planting sweet peas in your garden, try spacing the plants so they can get good air circulation which will reduce the chances of mildew.   

Botrytis – this is a fungus, which appears on sweet peas as a grey mould and is usually associted with damp. Therefore, whilst you are ensuring your plants remain well watered to try to prevent powdery mildew, you also need to be careful to not over water which can increase the chances of botrytis. You can prevent botrytis affecting your sweet peas by watering from below to avoid getting water on the leaves of the plants. You should also remove any dead or diseased plant material immediately to prevent the disease spreading. This, combined with the correct spacing when placing your plants, will help to reduce the chances of botrytis. 

Sweet Pea Colour Meanings
Sweet pea flowers are available in an enormous range of colours, from pure whites and creams, through to pastel pinks and blues and deep mauves and purples. The only colour which you won’t find as a sweet pea flower is yellow, as despite growers’ best efforts a yellow sweet pea has proved elusive.

With so many colours to choose from you might want to consider the meanings given to the different colours before deciding which to grow or which to give as a gift. Here are the general meanings we have found so far:

  • White Sweet Peas – peace, purity, spirituality, innocence
  • Orange Sweet Peas – enthusiasm, excitement
  • Red Sweet Peas – passion, love, drama, romance
  • Pink Sweet Peas – happiness, warmth, gentleness, non-romantic love
  • Purple Sweet Peas – royalty, pride, success
  • Blue Sweet Peas – rarity, uniqueness, desire, calmness
White Sweet Pea Blooms

You will also find sweet pea flowers which are a combination of two colours or contain water-colour style washes of colour. There are also varieties which are speckled – you may see these referred to by sweet pea growers as ‘stripped’ or ‘rippled’ (these flowers have a border or picotee edge) or ‘flaked’ (these have coloured markings that run across to the edge of the petal).

In the language of flowers, sweet peas represent lasting friendship, making them the perfect gift to give someone.

Sweet Pea History And Symbolism

The botanical name of the sweet pea is ‘lathyrus ororatus’ derived from the Greek word ‘lathyros’ meaning pea or pulse and the Latin word ‘odoratus’ meaning fragrant, so roughly translates as ‘fragrant pea’, apt as sweet peas are known for their delightful fragrance, with different varieties having different scents.

Sweet peas were first discovered in Sicily as a wildflower, recorded by a monk, Franciscus Cupani in 1695. He sent seeds to plantsmen in Europe resulting in the sweet pea becoming widely grown.

By the 18th Century, from the original sweet pea more colours were then available due to its’ tendency to mutate resulting in different colours and forms, yet all characterised by their distinctive scent.

Plantsmen continued to breed sweet peas so that by the middle of the 19th Century new colours were being bred commercially, and the Victorian era in England was when sweet peas became incredibly popular with sweet peas being given as a thank you gift to a host for a wonderful time. Credit for the popularity of the sweet pea is often given to the famous Scottish breeder of sweet peas, horticulturist Henry Eckford and the sweet pea became nicknamed the ‘Queen of Annuals' and was the subject of a famous London exhibition held at Crystal Palace in July 1900.   

Our growing sweet peas guide has been created from our personal knowledge, information gathered by speaking to other gardeners or manufacturers in the gardening industry, by reading gardening magazines and devouring information from books and the internet. We aim to be as accurate as we can, so if you find a mistake, please remember, we’re only human. if you have any queries you can contact us today!

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