Cool is the whole game
Peas are a cool-season crop and do not tolerate a warm reservoir. Keep water at 15–18 °C (59–64 °F) if you can; above 20 °C (68 °F) the plants become prone to powdery mildew and stop setting pods.
This makes peas a spring and autumn crop in a warm room. If your space runs at 25 °C (77 °F) in summer, grow peas in the cooler months and lettuce or basil in between.
They will take a light frost outdoors, which is why they are the first thing sown in a garden. Indoors, that cold tolerance is not useful — but the heat intolerance still is.
Feeding: light, like beans
Peas nodulate and fix their own nitrogen, so a full-strength vegetative feed gives you a large leafy plant with few pods. Run EC 1.2–1.6 and pH 6.0–6.8.
As with beans, in a fresh hydro system there may be no rhizobia present at all, so do not starve the plant entirely. Adequate rather than generous is the target, and a bloom or fruiting formulation suits peas better than a high-nitrogen one.
Sowing and support
Pea seed is large and germinates in 7–14 days. Sow direct, three seeds per net pot, and thin to two. Do not pre-soak — peas rot in water.
Dwarf varieties reach 40–60 cm (16–24 in) and need only a short stick. Tall varieties run to two metres (6.6 ft) and need netting or string. In a countertop system, the dwarf types are the sensible choice; the catalogue lists height for every variety.
Peas have tendrils rather than twining stems — give them something thin to grip, like string or pea netting, not a thick cane.
Harvesting
Pick young and often. A pea left to swell stops the plant producing more, and the pods become starchy. Check every day or two during the harvest window — the difference between a mangetout and a tough pod is about 48 hours.
For snap and snow peas, harvest when the peas inside are barely visible. For shelling peas, wait until the pod is full but before it changes colour.
If you want seed, stop harvesting and let the pods dry on the plant until brown, then shell.
Saving pea seed
Peas are the easiest seed crop in this catalogue alongside beans — they are strictly self-pollinating, and the flower closes before it opens, so crossing is rare enough to be ignored.
Let the pods mature fully on the plant until brown and rattling. If wet weather threatens, pull the whole plant and hang it upside down indoors. Shell, discard any seed with holes (pea weevil), and dry further for a week.
Stored dry in a sealed jar in the fridge, pea seed keeps four to six years.