Still time for Sweet Peas

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Growing sweet peas is a rewarding pastime for those of us who love scented cut flowers.  There are as many ways of growing them as there are gardeners, but one of the most frequently asked questions is when to sow the seeds for a decent display.  Down in the South, many growers will have started them off outside in September, but fear not if yours are still in their packets - you still have time to sow them in January, and this is often the accepted time for sowing for those in cold gardens, those further North or those with a greenhouse or well lit shed.  Planting directly into the soil later in the year is still possible, but you will tend not to have such a rampant display.

Many gardeners wonder why we go to the trouble of raising sweet peas from seed rather than buying the pre-grown seedlings from a nursery in March or April.  There is no definitive answer, but I have always suspected that seeds grown properly at home are much less stressed than those purchased from a bulk-forced nursery and are likely to produce a better display as a result.  In addition, growing from seed allows you to choose from a much greater variety of sweet peas, including successful historic species not available from the local nursery.  If this interests you, try buying online, or look out for the specialist sweet pea growers at flower shows such as RHS Hampton Court or RHS Chelsea.  Even the large seed companies such as Unwins or Thompson and Morgan have varieties available online that are not offered in the nurseries around us.

Some gardeners are concerned that sweet peas need large amounts of space and huge amounts of attention, but this is not necessarily true.  As well as the well-known climbing tall varieties, which really need to be planted into the soil, there are also dwarf versions such as Snoopea, which are suitable for containers and, supposedly, hanging baskets.  I will be trying to grow these and will report back if successful!

Sweet Pea Snoopea
Photo credit unknown

Some experts suggest that seeds will germinate better if they are soaked overnight (possibly discarding those that have not swollen), or if the seed coats are nicked either with a knife or by rubbing with sandpaper (on the side opposite the "eye" or the scar on the seed as damaging this is a sure fire way to kill off the seed).  However, opinions vary on this, as it was apparently suggested in the days when many seeds originated from hot climates such as California, where the seeds developed hard coats in response to the heat.  Seeds are now generally sourced from more temperate areas including within the UK, and this advice is now often ignored - some growers even suggest that soaking might stress and weaken the seedlings.  Please read your seed packets for instructions as to whether they need nicking or pre-soaking, or ask the specialist if you buy at one of the RHS shows - I have some seeds which specifically state that they should not be nicked or soaked (Heathcliffe and Cathy, to be planted in an area that is given over to plants with literary-related names such as Hosta Great Expectations and Rosa Lady of Shalott, since you didn't ask).

Although September sowings may be made directly into the ground, January sowings need to be made under cover (in a greenhouse or cold frame) as the soil will be too cold outside.  The seeds might need a gentle heat to germinate, although this is often not necessary.  If you do use heat, remove the seeds as soon as they have germinated as they will otherwise become very leggy.

Image courtesy of Thompson and Morgan

Sweet peas have deep root runs, and the seeds need to be planted in a deep pots or the equivalent.  Don't be tempted to use an ordinary seed tray as this is too shallow.  Some growers swear by toilet roll tubes (one per seed), as these can be planted complete into the soil without disturbing the roots, but if you have any realistic quantity of seeds you need a seriously incontinent family to generate enough of these tubes - and asking neighbours for theirs is a somewhat risky operation, often leading to strange looks and doors slammed in your face.  Besides, if you are planting in early January, many of the tubes will already have been used to make your own Christmas crackers! 

Generally, growers use 3 inch or 5 inch pots (1 seed per 3 inch pot, or 3 to 5 seeds in a 5 inch pot), but many report success with the new "Rootrainer" seed system that is sold in most garden centres.  This is composed of a frame which holds a number of modules (usually 32)  into each of which you plant a single seed.  The modules are reasonably deep and open up when you come to plant out the seedling to minimise root damage.  These root trainers come in a number of versions; "rapid" at 3 inches deep, "deep" at 5 inches and "maxi" at 8 inches.  The "deep" 5 inches are the ones that you need - although they are expensive, they can be re-used over and over again. The 8 inch version uses significantly more planting medium but gives little additional benefit for this cost.

The basic steps for success are, therefore:

• Check your packet / ask the supplier to confirm if the seed needs pre-treating in any way.  If in doubt, it is probably best to do nothing special;
• Plant one seed per module in a Deep Rootrainer, or one seed in a 3 inch pot, or 5 seeds in a 5 inch pot, using John Innes No 1 seed compost, or a multipurpose compost containing additional John Innes - the latter is often preferred as it contains more nutrients long-term.  Plant at about 1 inch deep;
• Water the pots and cover with a little damp newspaper to keep them moist and to keep out the light.  Rootrainers come with a lid, which can also be used to conserve moisture;
• Ideally set a mousetrap or take other precautions against rodents, particularly if sowing in a cold frame, as mice love the seed;
• Check the seeds for germination every day, remove the newspaper and/or lid, and keep them cool once they have germinated, particularly if they have had some bottom heat applied.  A cold greenhouse, coldframe or light shed is fine;
• When you have four leaves, or three / four pairs of leaves, nip out the leader to let them bush out;
• When the roots have filled the Rootrainer, or pot, and they have strong growth, plant them out after hardening them off.  They can go out before the risk of light frost has passed as they are hardy, but not before the risk of very hard frosts has gone as they are still delicate.  In our neck of the woods, this will be in late March or early April.

Check back in March for our next article on how to plant them out!