Sweet peas are frost hardy annuals. So there is no need to worry if a "normal" overnight frost in the range -1 to -4 degrees centigrade is forecast. If it gets colder than that, however, or if there is a prolonged spell of cold weather where the temperature does not go over freezing for days on end, then you might want to help your plants a bit. If they are still in pots or root-trainers, just bring them into an unheated greenhouse, conservatory, garage or shed.
If they are already planted, then just protect your sweet peas with some horticultural fleece and leave it there until the freeze is over.
Sweet Peas are natural climbers and so need something to climb up. There are various ways to do this, but whichever you choose, the support needs to be in place before you plant. All the methods of support listed are suitable for any of the range of sweet peas for sale on this site. Thinking about support after planting usually results in broken or trampled plants, compressed soil and a thoroughly bad mood.
Here are some of the more usual means of support:
The ground wants to be well prepared so dig in extra muck or compost because while sweet peas improve the soil by fixing nitrogen, to flower as freely and for as long as they are able they need plenty of available food and moisture. Organic matter helps improve moisture retention so add it freely.
With the support and soil sorted, your Ashridge Sweet Peas arrive, all pinched out so that they are nice and bushy and hardened off so that they can go straight into the ground.
There are two ways to grow sweet peas:
The amateur’s way (aka the "I just want a bunch of sweet peas in the house for most of the summer" way) or the exhibitor’s ("I want perfect blooms with immaculate straight stems and am prepared to put in the time to achieve this") cordon way! If you have not grown sweet peas before, we would recommend you begin with the amateur’s way.
Amateur sweet pea growers plant one or two plants about 5 cm away from their intended support by digging a hole that is about twice the size of the rootball that you have received. If you are gardening on very dry sandy soil it is worth putting some strips of damp newspaper at the bottom of the hole. Plant the sweet pea plug in the hole and cover it with soil up to the first side shoot. You need to firm in the soil so that good contact is made with the root but you don't want to compress it so much that you compact the soil. Water in well.
As soon as possible you should tie any shoots onto the support using flexi tie/sweet pea rings/garden twine. Doing this makes them grow faster and stronger. To start with you will do this every couple of weeks. Later in the season you need to do this more often and may even feel moved to remove a shoot or two if your framework is becoming very crowded.
As the flowers develop, pick them, and then pick them again. Picking the flowers actually encourages more to grow and obviously prevents them turning into seed pods. If you have the time, cut out at least some of the little curly tendrils that the sweet pea uses to grip the frame because the plant is putting lots of energy into producing these rather than flowers.
Sweet peas need lots of water so if it is dry, make sure that you keep the soil moist. Dry soil will encourage the flowers to go to seed more quickly and your sweet pea season will be curtailed. If your soil is poor you can use some of the potash fertilisers that you might have handy for your tomatoes to keep the crop blooming.
As the season progresses you will find that your flowers are borne on shorter stems which is perfectly normal. Keep deadheading and feeding and watering to keep them growing as long as possible.
Professional growers – including the amateur at your village flower show who manages to get six enormous flowers per perfectly straight stem and win first prize every year… use cordon training and layering and mainly grow Spencer varieties because their stems thicken up more naturally.
Start like an amateur but plant a single plant about 5 cm away from the cane to which it will eventually be tied.
Once the stems are about 20 cm long, choose the strongest, most sturdy stem and cut off all the rest from the plant with clean, sharp secateurs. Tie the chosen stem onto the cane using flex tie/sweet pea rings/garden twine and keep tying in as it grows. Remove all tendrils and secondary stems at the same time.
The flowers will be large and on long stems. There just won’t be very many on a plant at once. But if you keep picking they will keep appearing. Keep watering etc.
Now here is the clever/tricky bit.
Once a sweet pea has reached the top of its cane, untie it completely and lay it and its neighbours carefully on the ground. Beware! The stems are quite brittle. Take the stem of the sweet pea along the ground at the base of the canes and then tie it onto a new cane further along the row so that the top of this sweet pea stem is about 30 cm up its new cane. Do the same with all the other layered sweet peas. You then repeat the process of tying in the stems and removing the tendrils and side shoots as necessary. The sweet pea will grow and produce yet more show quality flowers on straight stems. With a bit of practice, you might give your local “amateur” at the show a run for his money/