Sowing Sweet Peas in Autumn – an expert’s view, by Phil Johnson
Much has been written over the decades about this subject and the key points continue to hold true to this day. I sowed my first Sweet Peas in Autumn in 1983 and have done so every year since, so I have a degree of hands-on experience. Our Autumn sown plants have been available for purchase from the Great Dixter Spring Fair and other events for many years.
Why sow in the Autumn
Earlier and longer to flower than Spring sown Sweet Peas.
Stronger plants with a good root system to get the plants off to an easy start in Spring.
Provides a Sweet Pea “fix” over the Winter months to keep your interest and a fascinating extension to the Sweet Pea season.
When to sow
Traditionally, sowing in the first week of October in the south of the UK was the norm. Temperatures would be warm enough to ensure fast germination in around ten days, without the need for additional heat. Temperatures would cool and the young seedlings would grow steadily over the winter, planting out in mid March.
However, global warming has had impact on the Sweet Peas as well. If you continue to follow these timings, in most years, the plants will put on too much growth and become a tangled mess; need feeding to keep them healthy; need larger containers to hold a larger root ball.
Bearing this in mind, my recommendation is to sow at the end of October. Your plants should then be at the best to plant out the following March.
How to sow
There are many different recommendations of compost and containers to use for Autumn sowing Sweet Peas. Rootrainers and toilet roll inserts are just two of the containers often mentioned; both have their merits. Whatever you use, the container needs to be relatively large to accommodate the larger amount of root that will grow in the Winter.
My preferred method is to use one litre or five inch pots. I tend to reuse plastic pots that I have had for a number of years, although recyclable versions are becoming available. Of course, Sweet Pea seedlings look amazing in traditional clay pots and “long toms” too.
I would recommend using a peat free multi-purpose compost. However, as this can be variable these days, try adding around one third John Innes number two, if the compost is very free draining or add about ten per cent Perlite, if the multi-purpose appears to be heavy.
I do not recommend soaking seeds in water, as this can cause some varieties to rot. The best method is to place some damp paper towel in a takeaway or sandwich box, then tip the seeds on top.
Place somewhere warm, such as an airing cupboard overnight. Examine your seeds and any that have not swollen may be “chipped” or filed with a nail file to allow moisture in to start off the germination process.
Then sow your seeds, as described below.
Fill your pots loosely to the top with compost, then water thoroughly and allow to drain. Next make up to six holes in each pot around one to two centimetres deep, a small dibber or old pencil is ideal for this. Pop a seed in in each hole and cover; then label.
DO NOT be tempted to leave indoors on the windowsill, in a heated conservatory or garden shed. All these places are either too warm or too dark to produce, strong compact, “cobby” plants. Instead, they will become weak and etiolated and of little use.
Ideally, place your pots - in order of preference – a cold frame, cold greenhouse, somewhere sheltered outside.
Cover the pots with an old compost bag or similar to stop the compost drying and check daily after a week has gone by. Remove the bag once the first plants emerge.
Protection against mice at this early stage is ESSENTIAL; slug prevention is sensible too.
An ideal Autumn sown Sweet Pea plant should:
Have a strong and substantial system of white roots
Have compact growth of a deep green colour
Be tough and already hardened off for planting outside in Spring.