Sweet Peas

Tim Sansom explains how to provide the heavenly scent of Sweet Peas for 9 months of the year

The Diggers Sweet Pea trial garden in January 2013

Sweet Peas are the easiest of garden flowers to grow, and our 2012-13 trials here at Diggers debunk the widespread belief that the Australian summer is too hot for these dependable flowers. Our research showed with a little planning you can enjoy up to 9 months of flowers a year.

Everyone loves a Sweet Pea!

Sweet Peas are somehow ingrained in our cultural psyche. Whilst most non-gardeners have trouble naming more than a couple of plants, the Sweet Pea is as well recognised and appreciated as a garden rose. Whether in the garden or in a vase indoors, the sweet scent and myriad of colours of Sweet Peas has meant that even those who have little interest in gardens have had some experience of the romance of this horticultural jewel.

Australian gardeners were particularly keen Sweet Pea growers with the introduction of the locally bred and early-flowering variety Yarrawa by Yates in 1911. This variety formed the foundation of a hugely popular series of Australian Sweet Peas that Yates offered for the next 50 years.

Such was the popularity of the Sweet Pea, the 25th edition of the Yates’ Garden Guide, printed in 1952, states ... “Our requirements each year are measured in tons, which is an indication of the popularity of the Australian Early Flowering Sweet Pea.”

The journey of the Sweet Pea, from Sicily to the World

The story of the Sweet Pea all began quietly enough in 1699 when a Sicilian Monk, Father Francisco Cupani sent a few seeds of the wild Lathyrus odoratus to his friend Dr Uvedale in the UK.

The resulting plants grew quietly in the Doctor's garden for the next 20 years until some flowers found their way to the London Flower Market where their heady fragrance earned them the nick-name ‘Sweet Pea’ and so this humble little creeper was on its way to stardom.

Cupani's original wild selection had a purple standard and a sky blue wing petal. Whilst the direct lineage from this original material can no longer be traced, the Auckland-based Sweet Pea breeder, Keith Hammett sourced wild material from Sicily in the 1970s and reintroduced this wild form as Original as the closest thing on the market to Cupani's original strain (the variety on the market as Cupani has no real claim on this title as it is not derived from the original stock, it just looks like the description offered at the time).

All the variety in colour, form and fragrance that was to follow was contained within the genetics of Cupani's original selection from the wild. Breeding development was initially slow with the release of the pink and white flowered Painted Lady being the first named cultivar offered in 1731. For the next 100 years Sweet Peas gained some popularity with English gardeners even though there were only a handful of colours available.

Towards the end of the 19th century the range expanded to some little extent. Breeders such as Thomas Laxton (famous for his Laxton's Superb Apple) and others were busy in the background while the prolific self-publicist Henry Eckford took centre stage. At the turn of the century, he lifted the profile of the Sweet Pea across England and networked with American growers so that soon gardeners and breeders across the Altantic were playing with Sweet Peas too.

Eckford is largely credited with the introduction of the large-flowered and hugely popular Grandiflora Sweet Peas – so much so that in history he is known as the ‘Father of the Sweet Pea’. Over the next 20-30 years there was an explosion of varieties on both sides of the Atlantic. By 1918 the Philadelphia based seedsmen, W. Atlee Burpee & Co were offering over 170 Sweet Pea varieties and a vast array of mixes.

Back in the UK, the next exciting development came at the hands of the Earl of Spencer's Head Gardener, Silas Cole. At the National Sweet Pea Society's first ever show in 1901, Cole presented (much to the anticipation of the waiting boffins) a variety he named after Princess Diana's grandmother, Countess Spencer. It displayed the unique characteristic of having a waved standard petal. This was a breakthrough described at the time thus ... “it seemed as if nature has been so lavish that the material in its standard had to be closely pleated to hold its position. It was beflowered and befrilled”. Subsequent breeding from Countess Spencer gave rise to the true Spencer Sweet Pea, with their characteristic wavy standard and open keel in a wide range of colours.

Flowers from September to April, Diggers 2012 Sweet Pea Trials

Whilst Sweet Peas have been a constant in our seed catalogue since Diggers began with cottage flowers more than 25 years ago, our list has dwindled in recent times, so we set about the task of assessing some new and interesting varieties in our trial garden.

As with all our vegetable trials, the only way to get decent information on varieties and how they perform is to grow them ourselves under the Australian sun. Through our close connection with the world renowned garden plant breeder, Dr Keith Hammett in Auckland, we sourced 26 varieties and so set about growing a field of flowers.

Initially we were curious to look at different flower colours, forms and levels of fragrance, but on talking to Keith about different sowing timings and the potential to extend the flowering season by using successional sowings, we incorporated a few different sowing times to observe the impact on flowering Many of you will be aware of the folksy tradition of sowing your Sweet Peas on St Patricks Day (March 17th). This is, in fact, a remnant of the specific requirements of Yates’ Yarrawa variety and is not such a neat rule of thumb when applied to varieties not originating from this stock.

Most of the Sweet Peas offered in Australia in the first half of the 20th century were known as Australian Early Flowering Sweet Peas as they were bred from Yarrawa, these varieties generally initiated flowering early in the spring (after an autumn sow) when the day length was no shorter than 10 hours a day.

The idea was that they would flower handsomely for a couple of months, then finish up before the onset of the summer heat. This had obvious advantages in our blistering summers, but it has meant that some of the best varieties don’t perform at their best with this sowing time as they need longer day length to flower properly.

In our trials we divided up the varieties into two groups based on the daylight hours required of each variety to initiate flower. The two groups were classified thus:

Short-Day, or winter-flowering types that initiate flower in 10 hours of daylight (the Australian Early varieties are this type). These will flower in the short-day months either side of winter, with flowering times determined by the sowing month.

Long-Day, or spring/summer flowering types that initiate flower in 11-12 hours of daylight. These will flower through the warmer months whilst the day length remains greater than 11 hours in the late summer and extends beyond 11 hours in the late spring, with flowering times determined by the sowing month.

As can be seen on the chart above we found that in our temperate climate (Heat Zone 4) we can get up to 9 months of flowering from September to May from the Long-Day types alone. A March sowing of the Short-Day varieties produced flowers as the day length hit 10 hours, about four weeks before the May sowing of the Long-Day types.

You can see in the chart above that Sweet Peas growing through the winter will grow slowly when the soil and air are cold, so will take much longer to get to a reasonable size to display flowers. In areas with mild winters the autumn sowing of Long-Day varieties can result in very tall plants that take longer to flower – but they will still flower as soon as the season approaches the spring equinox.

The other main consideration for us was to look at how Sweet Peas stand up to the summer heat when sown in spring, our results here were a pleasant surprise to us with impressive summer displays. With Sweet Peas being associated with cool English summers the general perception was that they could not cope with our scorching sun and hot, dry summer winds. It seems from our observations that beneath the Sweet Pea's delicate appearance lies a tough constitution that can withstand our southern summer heat, with our spring sown trials shaking off 42°C heat in early January to repeat flower happily through to February.

Tips on growing Sweet Peas

The Basics

Sweet Peas like a sunny open spot in the garden and their roots need access to some soil moisture in the warmer weather, so occasional watering will prolong flowering.

Soil Preparation

Sweet Peas will grow in any soil, but will perform best in a rich and friable loam. Heavy clay or structure-less sandy soil can be made suitable by the addition of ample organic matter. As with all peas, Sweet Peas don't like an acid soil, so if you have a pH under 7 it would be a good idea to add some hydrated lime before sowing.

Sowing

Sweet Peas can be sown indoors in trays for transplanting out or direct-sown in the ground. Our experience is that direct sowing works very well for the spring and summer sowings (provided the seeds are kept constantly moist until germinated) and indoor sowing will get the May sowing up quickly and increase the success rate. With all sowings, but particularly the cool season sowings, protecting the young seedlings from snails is vital.

Trellising/support

Sweet Peas attach readily to any open structure that they can get their tendrils around, from simple wire fencing, to cane tepees and elaborate arbours and lattice work. It is important to set up any support before sowing or transplanting so as to avoid damaging the young seedlings as they establish. There are some elaborate and fussy techniques recommended for those growing for exhibition, all of which are too much of a fuss for most gardeners because you will get ample flowers without such intervention.

Picking

In order to ensure repeat and extended flowering it is very important to pick the flowers as they open, if you leave the flowers on they will mature into seed pods and the plant will stop producing subsequent flowers. So pick what you want for inside and make sure any remaining flowers that you enjoyed in the garden are removed before they progress to pod formation.

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Tim Sansom

Tim completed a Grad.Dip. in Horticulture, ran a landscape design business and worked at Bendigo's Gravel Hill Community Permaculture Gardens before spending over a decade at Diggers as a gardener and Director of Horticulture.

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