Growing Sweet Pea: Basic Cultural Advice.

 

Sweet Pea need some sunshine: if you can't put them where the sun will light them for at least a couple of hours on a sunny summer's day, grow something else. They don't do well if their soil is often waterlogged: apart from that, they are not too choosy.  

 

Support. Sweet Pea need something to hold on to. They do very well on chicken-wire or sheep-wire, but plastic netting is almost useless. The ideal support is made of twiggy birch branches cut after leaf-fall, arranged either in a circle or a line.  These are favourites because they are wider at the top, where the Sweet Pea plant branches widely.  The trouble with wigwams is that they are narrow at the top. If you want to use a wigwam, try making the sticks meet half way up.   You need to get your supports installed and totally wind-firm just before planting out.

 

Soil.  Tall-growing Sweet Pea do appreciate being able to root down just a few feet, but they don’t expect you to do the work for them.  Merely forking through the top spit a couple of times to develop a good tilth will produce satisfactory results in most gardens.  Beware of giving Sweet Pea indigestion with too much organic matter or nitrogen-rich fertiliser, which produce lots of leaves but few flowers.  For best results, breaking up a second spit and incorporating a little leaf mould or well-rotted compost would be ideal, enriched with no more than 50 g/sq m of potato fertiliser.  The top spit should lie rough through winter frosts, and be cultivated to a fine tilth with a taste of a soil conditioner such as Danu two or three weeks before planting out.   If sowing in autumn, your site must be ready to receive the plants in March, so you probably need a plastic cover over it after final site preparation late in February.

 

Warfare.  The other basic preparation is to decide how you are going to succeed in keeping slugs and greenfly away throughout the season, and mice away from seed and baby plants.  Dedicated no-chemicals gardeners, please take this very seriously.

 

Selection.  The short and knee-high kinds of Sweet Pea are not suitable for most parts of Ireland, as they generally require more heat and light than our damp areas can provide.  For strong sweet scent there's nothing to beat the "Old-fashioned" varieties.  They are fine for scenting the garden or making a posy, but the flowers are small and plain and the stems are very short.  The multiflora kinds have more than five flowers per stem: these can make a good show in the garden but have limited use in the house because the bottom flower falls before the top one opens, and the individual flowers lack refinement.  The Spencer peas we work with grow to two metres high and have much larger, frillier flowers, generally four of them per strong stem in a more varied colour range.  Not all modern Spencer varieties are strongly scented but virtually all the whites, blues, and lavenders are.

 

Sowing time. For the best crop, October is best, December or January second best, March good, early to mid-April is not too bad, but May is no good - you miss half the season.  Plants sown in autumn or winter must have the protection of a sun-lit cold-frame or an unheated but sunny glasshouse.  

 

In Spring you can sow directly where the plants are to flower as soon as a sun-lit site is ready.  However, if there's no sunlight there at ground level in March, it's best to sow singly in 9-cm pots or root-trainers and stand these in a sunnier spot until you plant out a few weeks later on, when the sun rises higher.  Open ground for direct sowing needs to be brought to a fine tilth at least 10 cm deep, and to be moist but not wet at sowing time.

 

 

Germination. Germinate enough seed to allow for a few casualties: plan for at least 15 cm between plants.  If your soil is rich they can be further apart .

 

Don't listen to anyone who says you don't need to soak or chip Sweet Pea seed before sowing.   You should germinate the seed on a surface kept damp, (tissue, cloth or cotton-wool) at room temperature or not much below (65-68 deg F).   Cover fairly airtight so that their atmosphere becomes saturated.  Darkness isn't essential.  The coat of any seed that hasn't swollen after 24 hours must be nicked to let moisture in.  I use nail-clippers, but a file is OK, even a sharp wee knife can be used.  After nicking, put the seed back straight away.  After the seed has been four days in the damp, every day look it over and sow all that have the root-tip showing through the seed-coat.  

 

Sowing. Sow into the open ground, 9-cm pots, the largest size of root-trainers, or a deep seed tray.  You can use one seed-tray for all the seed of each sort, and transplant later, or sow individually at this stage.  Never do what most exhibitors do, and grow several plants in one pot: the root damage that occurs when untangling at planting time checks growth and invites disease.  A general-purpose peat-based compost is OK for winter and spring sowing, but loam-based John Innes No 1 compost is best for plants that have to stay in their pots from Autumn until planting-out.  Avoid composts that contain coir or other fibres.  They prevent the roots from being spread when you come to plant out.  Except in the seed-tray, all compost needs to be fortified with 3 g/litre of slow-release Vitax, Osmocote or MiracleGro Shake and Pour.   Sowing compost needs to be just moist enough to hold shape when squeezed, moist but not wet.  The sprouting seed should be covered 15 mm deep but not much more: this is deep enough to anchor the root and steady the emerging shoot.

 

Potting-on. If you use the seed-tray approach, pot on when the plants have two pairs of leaves, and nip the tip of the main root at the same time.  This will give a nice branchy root structure.  

 

Growing on. The hardier the plants are, the better they'll flower when Summer comes.  That means they need maximum light and air.  Through the Winter and early Spring, give the plants all you can, so long as they aren't deeply frosted.  Let them thaw slowly in the dark if the compost freezes.  Well-hardened October-sown plants will stand five Celsius degrees of frost well so long as you thaw them slowly.  Winter-sown plants in their early stages are checked by more than a degree or two of frost.  Only close down the cold frame or glasshouse if frost is likely, and open up as soon as the risk as passed.  It’s good to let light showers do your watering, but leave the cold-frame glass over to prevent heavy rains from leaching the nutrients out of the compost.  Prop it up to make a gap 10 cm high all the way round, then tie it down to cleats on the cold-frame unless you are gardening in a very sheltered locality.   When your plants have four pairs of leaves, nip out the top bud.  Basal shoots will then break out if they haven't already.  

 

Planting out. You should get the plants into their final position before the basal shoots are 15 cm long - 10 cm is better.  Spread the roots out a bit to give the plants a better "take".  The newly set out plants will need something low to hold on to and stop them swivelling in the wind.  Bushy twigs (birch again) 20 to 30 cm long poked in beside the plants do well, but poke some short bits in between the shoots as well.

 

Flowering. Flowering typically starts in late May from an October sowing, and two weeks later for every later sowing-time option. You should have buds showing colour six to eight weeks after planting, when the plants are about 75 cm above ground.  From now on, you may have to help the plants to hold on in the right places, but your main tasks will be to keep on cutting the flowers and keep the greenfly away.

 

Cooltonagh Irish Sweet Peas   

September 2004