How to grow sweet peas

Sweet Peas, latin name Lathyrus odoratus, look just fantastic as the images above show but even better they are one of the most sweetly scented of garden plants.  Sweet peas are long flowering and provide colour, scent and flowers to pick for months. Sweet peas are not difficult to grow but they do need regular attention throughout the summer. 

To keep them flowering it is important to dead head regularly. Removing the spent flowers prevents the plant from making seeds, which in turn keeps it producing more flowers and prolongs the flowering season.  Sweet peas also require attention, if you want straight stems, by removing tendrils on a regular basis, and they require watering during dry spells. The fact that sweet peas need so much attention is why they are tagged with a red wheelbarrow. The reward from sweet peas is their lovely scented flowers. The most important task is to dead head 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, dead heading keeps the plant going and if you do this you can be picking sweet peas right through to November.

When planting out sweet peas pick a sunny spot, and they like moisture retentive soil which needs to be 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. There is a Sunday gardener  Video How to plant and grow sweet peas



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 plant in a sunny spot. They are best grown with a support  such as trellis, obelisk or a frame and tie the sweet peas in.  

If you want straight stems, and sweet peas which grown up the frame and not a tangled bunch it is necessary to carefully remove 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, which is shown in the image above. Remove all seed heads as they form and the sweet pea will reward you with more and more flowers. 

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 some 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. 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 peas are vigorous climbers and will cover an arbor over the course of the summer making a tunnel of colour and scent.

Sweet Pea containers

Sweet pea containers

Sweet Peas are quick and easy to germinate and some 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 without any additional heat. When growing Sweet Peas from seed the choice of container is important. Sweet Peas, (like legumes all of the pea and bean family,) have long roots which means it's important to plant them into a deep container not a regular pot so they can develop those roots. You can use either root trainers sold by all garden centres, or cheaper and just as easy, toilet roll holders, both are shown in the image left. If you are sowing Autumn sweet peas to overwinter they are best in root trainers and there is a risk the cardboard tubes will get damp, disintegrate and /or encourage mould over the winter. Equally, the cardboard tubes are just fine for Spring Sown 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, if in a heated propagator remove so as to prevent the seedling getting too warm which will make it sappy and not very sturdy. 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. If the seedlings over heat they tend to go leggy and have less study stems.

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 more shoots which will in the summer will make more 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. 

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

The third image on the right was taken about 10-14 days later and after the growing points had been removed, 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 so much difficult, as time consuming. Once planted if the summer is dry they need regular watering as Sweet peas dislike being dry and if they dry become prone to mildew. To keep the flowering it is necessary to remove all seed head. 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.

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