How to grow Sweet peas
Everyone can enjoy a row of fragrant Sweet peas.
The potted seedlings often found in hot stuffy garden centre’s bare little resemblance to those you can grow yourself. They are crammed into pots, forced into with immature roots systems.
These Sweet peas rarely go on to make good plants. The disappointed gardener then blames themselves and thinks ‘wrongly’ that they can’t grow Sweet peas!
You can, and I’ll help by showing you how.
Let me start by explaining…
Types of Sweetpeas
The sweetpea we most commonly encounter is the ‘Spencer’ type. It has large frilly blooms on long stems beloved by floral designers. The ‘Spencer’ type has been subject to intense hybridization which has led to varieties with significant vigour which can grow to over 8 feet tall.
It is confusing that ‘Grandiflora’ types are actually smaller than the ‘Spencer’ type. The name comes from Henry Eckford when he first created varieties that were then bigger than any type previously seen. The term ‘Pre Spencer’ is sometimes used to indicate that these are the small flowers that also have plain petals.
The original 17th Century types. The flowers are smaller than both the above but what is lost in bloom size is made up in nostalgia and enthralling fragrance. These are easier to manage so an excellent choice for the home gardener wanting a simple jar for the nightstand.
Early Flowering Types
Most Sweetpeas are Summer Flowering. The day length is the factor that leads to flowering with ‘Spencer’ and ‘Grandiflora’ types requiring 12 hours of daylight to produce blooms.
‘Spring Flowering’ types require 11 hours of daylight to initiate flower while ‘Winter Flowering’ types will bloom with just 10 hours of daylight.
I also find their blooms to be more delicate in colour, like a watercolour and by far the most admired.
‘Multiflora’ Sweetpeas are those with more than five flowers per raceme (individual flower stem). The first variety was introduced by Suttons around 1930. Not as blousy as the Spencer’s they have not gained as much popularity despite the extra blooms.
How to Grow
We have found by far the most successful time to sow Sweet peas is to begin them in the Autumn. We find that plants are bigger, more hardy and much more vigorous than the same sown in the Spring.
If you have not started your Sweet peas in the Autumn then sow as early as you can in the Spring.
Seeds have a thick seed coat, so will benefit from a soak overnight in tepid water. The water needs to permeate the seed coat before the seed will wake from its slumber.
Once the seed has been soaked you should see the seed has swollen in size, but don’t worry if it hasn’t, this does not mean the seed will not go on to germinate, it just means the water is still making it’s way through and this will continue to happen in the pot.
Seeds are beloved by mice so for this reason I don’t personally direct sow outside. I like to sow 3 to a 9cm pot and keep them inside on the top shelf in my greenhouse but your kitchen windowsill will work just as well.
Keep them safe until the seeds have germinated and are pushing skywards through the surface of the compost…. Its them important that they have plenty of light.
Some people recommend planting root trainers or even empty loo rolls and over the years we have tried everything. I just find 9cm pots are easier, cleaner and a whole lot less fiddly – we always will opt for simplicity!
- Fill 9cm pots to the top with soil, tapping firmly against the table as you go, so the soil settles and there are no trapped pockets of air.
- Get your label ready, you forget very quickly what you have sown so write them first.
- Soak each variety in a few inches of water overnight with the plastic label in the jar.
- In the morning sow 3 seeds to each pot. Make a small hole with a pencil or dibber about 4cm (or knuckle) deep.
Smaller containers just 1 seed per pot or cell
- Cover with a light dusting of the compost mix or vermiculite
- Place freshly sown pots in a tray of water to soak them from underneath, overhead watering can dislodge those carefully sown seeds.
- Covering moist pots with a clear plastic dome will help keep a humid moist environment ( if sowing in early Spring I find providing a little bottom heat will help speed up germination. But the kitchen windowsill is sufficient if a little slower for successful germination).
- Don’t over water again until you see your seedlings emerge, the dome will keep the moisture in.
- Once seeds have sprouted, remove plastic dome lids and move them to a bright space such as a greenhouse.
- Check seedlings daily and water from underneath when the soil appears dry.
- As young plants grow, they need to be fed. Following the label instructions, add the correct amount of liquid seaweed to your watering can and add this to your watering trays. Seaweed is a brilliant all round feed and can also be used a foliar feed.
For Autumn sown plants we overwinter in their pots before planting out in March.
Pinching out the tip of branching plants is one of the most important techniques to give much stockier plants that will give you many more flowers.
How it works
Removal of the top shoots (apical buds) enables the sideshoots (axially or lateral buds) to branch out.
The top shoots would normally inhibit the sideshoots by producing hormones in a process called apical dominance causing the plant to just grow skywards.
Cordon training is used by professional growers and gardeners who regularly exhibit plants as it produces the best, top quality blooms. But it is labour intensive.
In the cordon system, sweet peas are trained as single-stemmed plants, tied to individual bamboo canes. All the sideshoots and tendrils are carefully removed when they form, so that all the plant’s energy is put into producing flowers, and the plants have to be tied in regularly to the canes.
Bush, sometimes known as ‘clump cultivation’, is when a whole pot full or several plants planted separately, are allowed to grow up a structure independently with an occasional tying in should it be required. With this method the flowers are early and the first flush have large stems and flowers. The sight and smell of a clump in full bloom is something special.
Sweet peas are ‘hardy annuals’ so will survive the Winter outdoors, however growing them in a warm environment will reduce their resistance to the cold so do ‘harden plants up or off’ before transplanting outside in the Spring.
Harding off is the process of acclimatising young plants to the outside temperatures and the wind and weather before putting them into the garden, otherwise they will be shocked by the sudden change in temperature. At best they will stall, at worst the plants will suffer damage and could die.
Set pots in a sheltered spot outside, increasing the amount of time they are out each day. This helps the young plants acclimatise to outdoor temperature fluctuations.
Sweetpeas can be planted out into the garden in September, they won’t grow much above the surface but the soil retains heat for a good while and the plants can put down good roots ready to get away quickly in the spring.
We also sow again an early Spring batch of Sweetpeas to extend the growing season and provide later Summer Brides blooms for their bouquets. Spring Sown plants can go out once all danger of frost has past.
Sweetpeas are hungry thirsty crops so take a little extra care when preparing your beds.
We tend to prepare our beds in the Autumn, digging the whole area over in incorporating well-rotted manure / compost as we go before covering the bed with weed matting to protect from weeds as well as helping the soil to warm up faster in the Spring.
Just before planting we will add a fertiliser to the whole area.
Plant pots 25-30cm apart into your pre prepared soil, making sure to water in well – this will also settle the soil back gently around the root ball.
If you are preparing your bed in the spring you can obtain good well rooted manure from the garden centre to improve soil structure and pelleted chicken manure won’t burn your plants.
It is a good idea to build your supports before planting… Plunging in canes later can damage the roots!
Sweetpeas are climbers. It is essential to give your Sweetpeas adequate support while still being able to easily reach each bloom to cut it before it has a chance to go to seed.
At Swan Cottage we have driven posts 1m apart to make a frame for chicken wire. We prefer this greener option where leftover plant material can be burned off at the end of the season and the support used again the following year.
Pea netting will be too tangled up to reuse and will end up in landfill or worse floating in the ocean!
For the home gardener a tepee canes or an attractive purpose made plant support can be sufficient.
Tie in sweetpeas as soon as they are tall enough and continue to check and tie in regularly throughout the season – we check ours daily and pinch off the tendrils that tend to reach out and clutch the neighbouring flower.
Note: Make sure you tie in the stem and not the leaves.
Water regularly, Sweet peas don’t like their feet drying out.
Sweetpeas are cool weather plants so its a good idea to mulch roots during hot spells to keep them cooler.
Once a week at least comb the plants looking for developing seed pods from flowers that you might have missed. If you let the pods develop flower production will slow and eventually stop with the plant thinking it’s don’t its job.
Sweetpeas are hungry plants, we add liquid seaweed to our watering cans switching to tomato feed as soon as blooming begins – feed weekly.
Picking regularly is vital – if not picked the length of stem or spike soon deteriorates.
Sweet peas will continue ever skyward to over 8 feet and far out of reach, but you can ‘stop’ them. This is a method of cutting the main stem at the desired height. The plant then wake up the side shoots, which will each start producing stems of beautiful sweet peas.
We have found that the side shoots never produce the mighty long stems of the main shoot but they are plenty long enough for most purposes.
I find I actually have to cut the first sweet peas shorter at the start of the season as they are too tall!
Cutting and Conditioning
Try and pick flowers in the cool of the morning or evening when the stems are full of water.
I pick and plunge stems straight into a waiting bucket of water (tepid not cold) at my feet before moving them to a cool, dark place for at least a few hours – preferably overnight.
Keep the cut blooms away from drafts as this will cause them to wilt prematurely.
This is a common condition when buds fail to develop and drop off. It is not fully understood but extremes in temperature and fluctuates in conditions often result in the plant ‘blowing off’ flowers as some sort of safety valve. The plants quickly recover.
Symptoms of leaves that turn prematurely yellow beginning at the base of the plant can be caused by accidentally damaging the plant by digging at the base or by a pest doing the same or from a nutrient in balance. Prematurely is the key since all plants show some loss of their eldest leaves as they mature.
Mildew is caused by a fungus which favours hot dry conditions. It’s very common and is evident and easily recognisable since the leaves are covered by a powdery white substance. Maintaining a higher humidity around the plant may reduce this disease. This can be achieved by spaying the mulch (see maintenance above) with water and placing shallow trays of water near the plants to evaporate upwards on hot days.
Slugs and Snails
Mostly this is only really a problem when plants are young and newly emerging or just transplanted, once the vines are away you should have no problems unless your conditions are excessively damp.
This are annoying tiny black creatures that invade blooms, I don’t know if they are more attracted to white blooms are it’s just that I can see them? The solution is to stand newly cut flowers in buckets of cool water in a dark shed or garage with the door or window open, then pollen beetles will then be attracted to the light and all but a few will remain by the time you return to collect your flowers for arranging.
Aphids or Greenfly
Of all problems this is the most likely to arise. Luckily there is much that can be done. You can gently shake greenfly from a freshly cut stem by holding it upside down and giving a gentle but determined waggle.
Aphids all breathe through their skins so an organic solution of soft soap (washing up liquid) in a spray bottle applied at frequent intervals as well as plenty of chemical solutions. Whatever you use, spray in the evening or the liquid may cause the plant to scorch in the sunlight and any chemicals may affect the Bee’s.
There are many many more pests and diseases that could affect yours plants but these are the most common and good plant health will protect you from the majority.
The choice is endless and can seem overwhelming and you should choose according what colours you would prefer to grow:
Some of my favouries included
Spring Sunshine Champagne, Charlies Angles, Ethel Grace, Gwendoline, Our Harry, Sir Jimmy Shand, Valerie Harrod, Matucana
If you still can’t decide I have found that Sweetpeas with The RHS Award of Garden Merit (AGM) have performed the best for us.