Just been looking at DD's photos of his peas, I've been trying to grow Kelvedon Wonder for 2 seasons, in the past they never seem to grow to 18 inches as stated on the pack, and yield is quite low. DD's peas seem a lot taller (than 18 inches), and bushier than mine ever do anyway, and he said they were KW. Would adding horse manure (well rotted or fresh?) before planting, then feeding with something later help. The soil is quite heavy/sticky on my allotment. Any advice please.