How to grow sweet peas

Sweet Peas, whose Latin name is Lathyrus odoratus, look fantastic as shown in the images, and smell even better. They are one of the most sweetly scented of garden plants.  Sweet peas are annuals, which mean they germinate, grow, flower, set seed and die all in one year and so have to be re-grown each year. Sweet peas are long flowering and provide colour, scent and flowers to pick for months. Sweet peas are not difficult to grow, but they need regular attention throughout the summer.  I grow them every year and when in full bloom they need at least 30mins+ a week to dead head, take off the tendrils, train and tie them in. For this reason they are a red wheelbarrow plant.

To keep Sweet Peas flowering all season it is important to dead head them regularly. Removing the spent flowers prevents the plant from making seed, which keeps it producing more flowers and prolongs the flowering season.  Sweet peas also require attention, if you want straight stems it is important to remove the tendrils regularly, and they require watering during dry spells.  The reward for all this attention is their lovely scented flowers. The most important task is to deadhead the flowers as they fade and form seed heads, this ensures the Sweet Peas flower for a long season. If Sweet Peas are not regularly dead headed, the blooms will get fewer and fewer, and eventually stop flowering, With regular dead heading Sweet Peas can flower through to November.

When planting Sweet Peas select a sunny spot bearing in mind Sweet Peas have a strong preference for moisture retentive soil enriched with compost or other organic matter. If you encounter any problems growing Sweet Peas, the most common problem is powdery mildew, a fungus which leaves white powder on the leaves. This fungus is much more likely to attack the plant if it is dry, which is why it is so it is important to water sweet peas, especially in any dry periods and to have plenty of organic matter in the soil to retain water. There is a Sunday gardener Video How to plant and grow sweet peas.

Sweet Peas are a popular choice for planting in containers. All plants grown in containers are prone to drying out more quickly which does make them prone to attack by mildew. If you are growing Sweet peas in containers, consider adding water retaining gel and a good mulch to retain moisture. It also follows they will require regular watering, especially during dry spells.

If growing annual Sweet Peas is too much trouble, check out the Everlasting Sweet Pea which has the same lovely delicate flowers, albeit not scented, but as a perennial will return reliably and flower year after year.



Sweet peas on Arbour

Growing Sweet Pea tips

 Plant out in spring when the risk of frost has passed. Sweet peas are half hardy so can go out earlier than bedding plants, but avoid spells of cold wet weather. Sweet peas will withstand cold but if frost threatens, although hardy, they are best protected with a fleece.

Sweet peas like rich soil with plenty of compost and to be planted in a sunny spot. They are best grown with a support such as trellis or an obelisk and tie the sweet peas in.  

If you want straight stems, and sweet peas which grow up the frame and not a tangled bunch it is necessary to remove carefully the tendrils and not to let these grow unchecked.  Why?  See how to get straight stems on sweet peas.

Best tip: The more you pick and remove the seed heads, the more sweet peas flower. The tip is to Pick, pick, and keep picking sweet peas, don't let the seed head form. If you are not sure about seed pods check out the image above, the seed pod is ringed in red. Remove all seed heads as they form and the sweet pea will reward you with more and more flowers. 

How to Plant and Grow Sweet Peas

How to Grow Sweet Peas from Seed

Sweet Peas are easy to germinate and buying seed gives you a wider choice in terms of fragrance and colour, but it is more time consuming. Many of the garden centres sell Sweet Peas seeds in mixed colours which is good, but it is also nice to have single colours to contrast and complement other summer flowering plants. This type of Sweet pea is an annual which means it will only flower for one season.

This last year, for the first time I had to buy Sweet peas from a garden centre as opposed to choosing my own varieties and growing from seed. I have to say I was disappointed. The shop bought Sweet peas did not have such lovely blooms, and colours. The stems were not as long and the fragrance not as good. 

There is a perennial sweet pea called Lathyrus latifolius which blooms every year and the flowers look very similar to the annual variety, but many of the perennial varieties are not scented. Sweet Peas are seeded in either Feb/March for planting out later in the year, or in the Autumn for the next year.

Sweet Pea containers

Sweet pea containers

Sweet Peas are quick and easy to germinate, a little heat will speed up germination, but it is not essential. You can germinate Sweet Peas on a warm windowsill, conservatory or using heated propagator to get a temperature of about 15C/ 59F. Autumn sown Sweet Peas will germinate in a greenhouse/lean to with no additional heat. When growing Sweet Peas from seed the choice of container is important. Sweet Peas, like many legumes including peas and beans have long roots which means it's important to plant them into a deep container, and not a regular pot to give a long root run.

You can use either root trainers sold by all garden centres, or cheaper and just as easy toilet roll holders, both are illustrated in the image left. If you are sowing Autumn sweet peas to over winter, they are best in root trainers as there is a risk the cardboard tubes will get damp, disintegrate and /or encourage mould over the winter. Equally, the cardboard tubes are fine for a Spring sowing of sweet peas, just take care when watering not to soak the tube.

Put two/three seeds into the container placing the seed near the top to give plenty of room for the roots to grow down. Sprinkle with a light covering of compost, spray with water so the compost is moist, but not too wet and place in a warm place. It's essential for germination to cover with a lid or clear polythene. Germination should occur within a few days and as soon as the sweet pea seedling is a few centimetres above the soil, remove from the propagator or take off the cover to prevent the seedling getting too warm which will make it sappy and leggy. Only use the heat to speed up germination. It is very important not to allow the sweet peas too much heat after they have germinated, or to keep the propagator lid on for too long. 

When and how to sow sweet peas

Sweet Peas sown into root trainers

 Sweet peas can be successfully germinated in the Autumn in a warm conservatory and then moved into an unheated greenhouse for the winter. Provided the sweet peas are protected from frost under glass, they will overwinter and produce sturdy plants for the Spring. Autumn sown sweet peas tend to flower earlier and by sowing both in Autumn and Spring the flowering season is extended. 

Take out growing point

Whether you sow in Autumn or Spring, with young sweet peas at the seedling stage if you pinch out the growing point it will make the seedling produce throw out shoots and the additional shoots will bear flowers. 

Looking at the images below, left the first image shows the young sweet peas with several early leaves already formed, and using secateurs to show where to remove the growing point. 

The second centre image shows the whole tray of seedlings in which every seedling has the top growing point removed. 

The third image was taken about 10-14 days later after and you can see instead of just the single stem, there is now a side shoot. Pinching out the growth point makes the sweet pea produce multiple stems not just one. Autumn sown sweet peas, and peas sown early in the season will often need pinching out several times to nip out the top growth before planting out.  

Sweet pea cutting back growth point

Sweet pea cutting back growth point

Sweet pea all growth points removed

Sweet pea all growth points removed

Sweet pea after cutting back growth point has new shoot

Sweet pea after cutting back growth point has new shoot 

Red Wheelbarrow means that Sweet Peas are more time consuming to grow. They are not difficult to grow just time consuming.

Once planted if the summer is dry they need regular watering as Sweet peas dislike being dry when they are prone to mildew.

To keep the flowering it is necessary to remove all the seed heads.

To keep them straight and looking good, it is also necessary to remove all seed heads.

Growing around 50 or so plants for a good display this take take an hour or two couple of times a week during the high summer, which makes for high maintenance. 

Updated 07.03.2020