The elegance and fragrance of sweet peas in the spring - summer garden captivates and enchants many gardeners, florist and bouquet customers. Prized for their delicate blooms and intoxicating fragrance, they are easy to grow and mix well in the herbaceous border and into cut flower production.

Sowing Sweet Peas

TIMING

We recommend sowing sweet peas anytime from late March - August. When we transplant into a poly tunnel, we sow them earlier. The earliest blooming varieties will flower with shorter day length lending them to Autumn sowing dates. Consideration must be given to the heaviness of the soil in winter, though, as sweet peas detest wet feet, and protection of the flowers from late winter/spring storms, wind and frost. Also, depending on when the heat in your area really starts to increase in late spring, sowing earlier will give you a longer bloom season.

While sweet peas are cold hardy, best to wait until the nighttime lows are above -5°C before transplanting. Start your seeds indoors 10-12 weeks before your transplant date which can be around the time of your last frost.

POTS

Deeper pots allow sweet peas to develop a strong root system ahead of transplant. Forestry tubes (50mm x 50mm x 120mm) or 5” root trainers are recommended. These longer pots allow for the deep rooted nature of the sweet peas. If you are sowing in late winter, these pots will be enough. If you are sowing in late Autumn, watch the bottom of the pots. If the roots begin to poke through and the weather is still too cold for transplanting, pot up your sweet peas into a 1L pot. If they become root bound, they never recover.

PROPOGATION MIX

Use a peat moss, multi-purpose propagation mix that has been watered into the pot as opposed to packed tightly. We use our seed raising mix (recipe found here) which includes a base fertiliser with great results.

SOWING

Depending on the germination rate listed on the packet, sow 1-2 seeds per pot, 5mm deep lightly covered with propagation mix.

OPTIMAL GERMINATION TEMPERATURE is 10°C. If you are sowing in late autumn or winter, your seed may require additional ambient warmth during the night. Be careful with bottom heat, though, as it can overheat!

We also have great success, germinating the seed in paper towels in a cool room and immediately after the rootlet breaks out, we transplant into the ready pots. This is extra work but can ensure that no space/resources are wasted.

We do not recommend soaking sweet pea seeds although this is recommended by many great growers. Depending on where sweet pea seeds are produced, they can form an unnaturally hard seed coat. Our recommendation is based on our own seed production - our germination tests have not shown that chipping, sanding nor soaking are required to induce germination.

Germination can take 14 - 21 days. Throughout this time, keep at the optimum temperature and protect from snails, slugs and mice.

GROWING OUT A SEEDLING

Once germinated, give the seedlings lots of light to ensure they do not become leggy.

Sweet peas can tolerate light frost and should be grown as hard as possible - moving them out of the glasshouse on sunny winter days.

Protect from heavy frost (below -5°C) and strong winds.

Do NOT pinch autumn sown plants. Later sowings though, pinch the tip when it is about 10cm tall to encourage side shoots to develop. Roger Parsons, a leading UK sweet pea expert, in his book SWEET PEAS - THE ESSENTIAL GUIDE, states, “ [Autumn] sown plants grown cold will have reached 75mm high by [Winter] and side shoots will form naturally at this time….Left unstopped, those side shoots that are starting to form in [Winter] will be just the right length for planting out in early [Spring]. It is the cold weather that encourages natural side shoot development.” He goes further to suggest that if by this time, you are not seeing side shoots in a plant, this is the time to pinch it.

TRANSPLANTING

The ground where the sweet peas will be planted should be well amended - sweet peas are hungry and benefit from well rotted. manure laid into and then lightly incorporated into a 30cm trench where they are to be grown. The soil should be loose - sweet peas have deep roots - and well draining. Excessive dampness in the soil will promote fungal diseases.

Sweet peas thrive in full sun but also benefit from late afternoon shading as they dislike heat.

Plant at a depth where the root ball is just covered.

Water in deeply and continue to keep well watered - but not soggy.

Support of some kind is necessary - unless a dwarf variety, most sweet peas will achieve 180-200cm in height. There are many options in the home garden - such as a teepee, arch or tunnel. For later plantings, 2+m stakes can be set every 3m and then two layers of hortonnova netting, one over the other, can be used to create 180m of growing surface for the pea tendrils to grab. Metal fencing can also be used.

Wind breaks are very helpful in not only protecting the young seedling but in producing higher quality blooms.

Spacing varies from 18cm - 30cm depending on the support used. We sow 2 rows on either side of the trellis at 22cm spacing.

Continue to ensure that sweet peas are secured to the trellis. This encourages the upward growth of the plant and strong, long stems on the blooms. You can use twist ties, metal rings, clothes pins and/or twine for this task.

Protect newly transplanted seedlings from slugs, snails, mice and magpies.

Harvest/Vase Life

Sweet peas have a short vase life - 4-6 days. To try and extend this, harvest in the coolest part of the day, when one-two flowers are open and put a bit of sugar or flower food into the vase water. The remaining flowers will open extending the vase life.

Resources

If you have been caught by the sweet pea bug, the following experts are well worth reading

Roger Parsons - I highly recommend his book Sweet Peas - An Essential Guide

Dr Keith Hammett

Erin Benzakein of Floret Farm