Cultivation Advice

Ground Preparation

Sweet peas are quite greedy creatures. Although they will grow in most soils they will benefit from a little ground preparation. Well-rotted farmyard manure dug into the ground in the autumn will suit them well. However, if you don't get going until spring, the use of a proprietary brand of composted manure, the contents of your compost heap or a dose of blood, fish and bone will do just as well. Sweet pea enthusiasts all have their own special recipe for success but the most important thing is to give some goodness back to the soil each year.

Seed Sowing

Sweet pea seed can be sown in the autumn or spring. The seed should be sown 15mm deep either singly in 8cm pots or 5 or 6 seeds to a 13cm pot. We use a peat based multi-purpose or potting compost.
If seed is sown in October it will usually germinate without heat in a greenhouse or cold frame. We grow our plants in large well-ventilated polytunnels. We keep the tunnel closed until the seed has germinated. Once the shoots are through we begin to leave the doors open, firstly during the day and eventually at night unless the temperature falls very low. As a general rule until the end of December we would shut the tunnels at night if the forecast was for less than zero degrees C. If -3 degrees was forecast we would provide some heat. As we move into the new year we treat them progressively harder so that by the end of February they are conditioned to cope with most night temperatures.
For the gardener at home a cold frame is the best place to grow autumn sown sweet peas. Once the sweet peas have germinated the top lights can be removed and only replaced on cold nights or during heavy or prolonged rain. During exceptionally cold spells extra protection can be provided by covering the frames with old carpet or newspaper.
Sweet pea plants can be over wintered in a glasshouse but need vigilant care. In winter and early spring a closed up greenhouse can build up a surprising amount of heat. Sweet peas hate getting too hot and can very quickly get drawn and weak. It is essential to keep the greenhouse cool and well ventilated.
If seed is sown in early spring it will usually need some heat to germinate. A windowsill in the house is usually ideal. However, as soon as the shoots appear the pots should be placed somewhere cooler such as an unheated greenhouse or coldframe and gradually acclimatised to outside conditions.
Alternatively , you can sow sweet peas straight into the ground or in pots outside in April or even May. However, these will be some time before they flower. You will get much better value if you sow earlier.

Stopping or Pinching Out

During January for autumn sown plants, (later if spring sown), when the plants have at least two pairs of true leaves, we stop them. This involves cutting out the main shoot above the second pair of true leaves. This encourages the growth of side shoots from the leaf axils. It is these side shoots which will grow to give a magnificent show in the summer.

Pests before Planting

Two major pests to protect against:

Mice love sweet pea seeds as they germinate and can do irreparable damage before the plants have a chance. If mice live nearby either set traps or enlist a cat's help. The most serious risk of damage is at germination stage but at our nursery mice have been known to nibble the leaves on more mature plants.
Slugs love the young leaves of sweet peas and prevention is needed from the time they germinate until they are safely growing out of harms way.

Planting

For a good show of sweet peas, plant them 15cm to 20cm apart either in rows or in a clump. Protect them from slugs. Then, all you need to do is provide them with something to climb up. This could be netting, bamboo canes or some fancy support system bought at the local garden centre. The only important criterion is that it won't blow over. You will need to tie up a few shoots at the start, and occasionally over the summer, but generally they'll find their own means of support. If you live in a particularly cold area, it would be a good idea to purchase a length of frost fleece. Although the sweet pea is a hardy annual and even if your plants are carefully hardened off, a very severe frost following a period of mild weather can seriously check the plants growth. Covering the plants with the fleece when a very cold night is forecast is a very simple preventative measure.

What to do During the Summer

Pick the flowers and keep picking. You must keep on top of this. If the flowers are allowed to set seed the flowering period will be reduced. If you have to go on holiday ask your friends to come and help themselves to flowers. Watering may be necessary during dry spells. Sweet peas do not like dry soil. Feeding requirements will depend on how well the ground was prepared before planting. If the plants seem hungry a liquid feed may prove beneficial.

Problems after Planting

The sweet peas greatest enemy is the greenfly. If allowed to run riot it will sap the plant of its energy and cause the flowers to become distorted. They are also the means of spreading disease. Keep vigilant and take steps to control greenfly as soon as it appears.
The second common problem isn't really a problem (unless you especially need flowers for a particular occasion.) Quite often, usually at the beginning of the flowering season, the flowers will begin to form, but then the buds drop off and you end up with a bunch of stalks. This is 'bud-drop' caused by over-watering or sudden changes in the weather, usually conditions that are beyond your control.
Thankfully, it is a short-term problem and a week later you will be picking magnificent flowers again.

The Experts Method

If your sights are on becoming next years sweet pea champion at the local flower show or perhaps even at national level, your approach will need to be a little different. To achieve the perfectly formed large flowers and long straight stems, the plants need to be grown on the cordon system. This method of growing cannot be described in a single paragraph, but essentially means allowing only one of the original side shoots to grow, and from then on removing all side shoots and tendrils thus concentrating all the plants energy into forming quality flowers. It does involve a lot more work but can be very rewarding. There are several books available on the subject. Useful advice can be obtained by joining 'The National Sweet Pea Society' whose secretary is Mrs. M. McDonald, 'St Annes', The Hollow, Broughton, Stocksbridge, Hants. SO20 8BB. Telephone: (01794) 301490.