Hints on Growing
It was originally intended that this Section should be headed "How to Grow" but since there are so many opinions from different people, many of them contradictory, it is considered that there is no "right" way and so what follows is more properly considered to be hints.
The most popular type of Sweet Peas and those more generally seen at shows are described as Spencer varieties. These are the ones with long stems and large,wavy flowers. There are however several other types, illustrated in the Gallery. The following hints are primarily based on Spencers and other summer flowering varieties but essentially apply to other types.
Seed can be sown October to mid-November, “Autumn Sowing”, but this is more likely to be used by those who wish to have blooms for early exhibitions. Most people use “Spring Sowing” which can be anytime from January to March/April. Most suppliers of seeds recommend that seeds should be sown “dry” but some consider that “pre-germination” by soaking the seeds will give better results. One variety that I grew recently gave less than 10% germination when sown dry but when I contacted the supplier he replaced, free of charge, on condition that I pre-germinated – result,100% germination.
Some further hints relating to early flowering and Lathyrus are given below.
An article from the 2014 Annual by experienced grower Alec Cave, "Growing Sweet Peas - the basics", is also reproduced
Seeds should be sown in pots or seed trays then covered with 1 to 1.5 cm of compost. A 125 cm pot will hold about 12 seeds, 8 around the edge and 4 in the centre – a standard seed tray about 50 seeds, arranged 10x5. Level the compost and water with a fine rose. Covering with newspaper or propagator lids will help to avoid drying out. Germination is probably best at 15C to 18C and can take place in 5 to 8 days.
The planting area should have been prepared in Autumn, incorporating initial nutrients. Autumn sown plants should be planted out about mid-March and Spring sown a month or so later. Individual plants should be placed in holes and the soil level brought back to a level below the first side shoot and planted firmly but lightly to ensure good soil contact.
This gives the best way of developing growth and this is done into, typically, 7.5 cm pots or alternatively “root trainers” which are about 125 cm deep. This should be done as soon as seedlings can be handled when they will be 2.5 to 5 cm high. Lower the taproot into a dibber hole in the compost, tap the pot to settle the compost, which should be level with the original depth on the stem. Gently water in. Root Trainers are a frequently used accessory.
Autumn sown seedlings should be placed in a cold frame to over-winter. They will stand moderate frost.
Spring sown should be kept in a cool greenhouse.
If plants are to be grown on the cordon system, once the side shots are about 20 cm long it should be decided which is the strongest stem, not necessarily the longest, and then all other side shoots should be removed. (Sometimes two stems may be retained). As growth progresses the stem(s) should be trained to their canes, using rings or other methods. Side shoots and tendrils should be removed. Once flowers are available they should be cut regularly or dead headed to ensure no seeds are produced, otherwise flowering will cease. Layering will be necessary for cordon grown plants.
Non-cordon plants grown more for garden decoration or cut flowers require less intensive care, but still need tying in as the side branches develop and perhaps a little thinning out.
Spring sown plants should have their growing tips of the primary stem pinched out after two pairs of leaves have been produced, to ensure the development of side shoots. Autumn sown plants will normally produce side shoots naturally but the primary stem should be removed before planting out.
Little feeding is needed if the ground had been suitably prepared. These plants fix nitrogen from the atmosphere so additional fertilisers should be high potash and phosphate, to encourage flowers rather than green growth. Liquid feed at dilute concentrations (half or even quarter strength) can be applied at root level or as a foliar feed. Care should be taken to ensure that roots do not dry. Under very warm conditions it can be beneficial to spray, below flower level.
In frost-free areas, it is possible to sow early-flowering varieties in mid or late Summer
to have them flower during Winter. In colder areas, early-flowering varieties should be grown by one of these methods:
* In a heated greenhouse to flower from late Winter onwards by sowing in late Summer;
* In an unheated greenhouse to flower from Spring onwards by sowing in Autumn;
* Outdoors, treating as Summer-flowering varieties to achieve earlier-flowering
Annual Lathyrus species
The most popular time for sowing annual species is the spring. There are two exceptions to this, L. chloranthus and L. paranensis should both be sown in the autumn as they are later flowering. With other species, autumn sowing may get flowers as early as May, which may be better in climates with very hot summers. Sowing at different times can also achieve a succession of flowering.
Perennial Lathyrus species
Perennial species can be grown from seed sown at any time but for best results sow in the spring. This is to maximize the growing time to make strong plants that can over winter more successfully. Sow as with annual species. Germination can take anything between two weeks and two years, so be patient. Seedlings should be grown on in pots until they are big enough to be planted out in their final position with some support for those that require it. Most species require good drainage at all times, so add some coarse grit to the compost. Each species grows best in the conditions of its natural habitat.