Sweet peas are the most romantic flower in the cutting garden and the most demanding. They want deep, rich soil, cool roots and something to climb, and in return they give stems of intensely scented flowers from spring into early summer. The climbers reach 5 to 6 feet on netting or a teepee of canes; the bush types stay at 1 to 2 feet.
Sow in deep pots or root trainers in late winter, six to eight weeks before last frost, and plant out 6 inches apart as soon as the ground can be worked; in zone 7 and warmer sow in fall for an earlier, stronger crop. Pinch the seedlings at three pairs of leaves for bushier plants. Keep them watered and mulched, because they hate heat and decline fast once summer arrives in earnest. Tie them in as they climb.
Cut every single stem, since the more you cut the more they produce, and a plant allowed to set seed shuts down within days. Pick when the lowest flower on the stem has just opened, early in the morning. Deer leave them alone; slugs and mice do not, and the seed and pods are poisonous, which is why sweet peas are never grown as a vegetable. They are native to Sicily and southern Italy.
Powdery mildew
White or grey powdery coating on leaves - usually starting on older growth in humid conditions or when nights cool.
Improve air circulation by thinning plants. Apply neem oil or potassium bicarbonate spray at first sign. Avoid overhead watering.