This is one of my hand-made hybrids, Mr Bethell's Purple Podded x Alderman being grown for seed
I've now started harvesting some of the pods from my hand-pollinations, at least the ones that have had longest to mature. It takes about 5-7 weeks for peas to produce fully mature pods, depending on the variety, the weather, the growing conditions and how early in the season they were pollinated (the earliest flowers on the plants will usually produce the best seed, but may take longer to develop).
If you look at any seed saving guide, the received wisdom for peas is to leave them on the plant until they're fully dry, i.e. when the pods are brown and crisp and the peas inside are starting to rattle. And that's perfectly good advice if you're bulk-saving seed from a whole crop, especially if the weather is dry in the time leading up to harvest. But if you've put a lot of work into doing hand-pollinations then every pod matters, so I tend to harvest them individually as soon as they reach maturity.
Maturing pods of Kent Blue, which are unusually knobbly so you can see clearly how the baby peas are getting on
With tall peas it's very obvious when they have reached the end of their productive season. Their first step is to stop flowering, or produce only tiny unproductive buds. And then they flop. Big time. You should see my Golden Sweet crop now ... no sooner had I posted the picture of it standing six feet tall and full of bounty when it just collapsed, more or less overnight. It's now leaning over its bamboo frame in a great sagging heap. And damned heavy it is too, like a dead weight ... and one that makes a strange squeaking noise as the stems rub together. It doesn't look very glamorous but it's a perfectly natural event. Pea plants are short-season annuals and as soon as they've completed their production they naturally keel over and die.
In my experience, and this may be related to my garden's climate, the plants and the pods are vulnerable to a few problems at this stage. Once they've sagged, all the leaves and pods are pressed together and not very well ventilated, so if the weather is moist they can suffer with mould and mildew. Snails also like to crawl up and hide in the leafmass, where they seem to take a special liking to the mature pods even more than the young and tender ones, and chew great lumps out of them. These problems are obviously worse in damp weather, and if there's a lot of rain it's possible for the peas themselves to swell too quickly for their skins, and split open. It's also around this time of the season that the larvae of pea moths pupate and drop out into the soil to wreak havoc next year.
It takes a while for the pods to dry completely on the plant, but a while before that they go through a phase when the pod starts to change colour slightly or look a bit washed out and the surface goes leathery. The calyx (that's the little pixie hat at the top) dries up and withers, and the top of the pod starts to look a bit dehydrated and sunken where it joins on to the stem. (Picture on the right shows Carruthers' Purple Podded just approaching that stage.) I asked myself what message the plant is giving to the pods when this happens. I think the message is basically "right, that's yer lot!" The plant has been nourishing the pod all this while and now it's starting to withdraw its support. Any further nourishment and moisture the peas need have to be drawn from the pod itself, which is why the pod starts to look so leathery and drained. If the peas are no longer receiving moisture from the plant then there's no particular reason to leave them on the plant, as far as I can see.
So my rule of thumb is to harvest each pod when the calyx has withered, because the peas will have developed as much as they're ever going to, and may as well finish drying in a sheltered place.
Once harvested you can just leave the pods to dry out naturally, and shell them out when they've gone crispy. It normally takes three or four days at room temperature for the pods to dry down, and then they start to shrivel quite rapidly. (The peas themselves will take a while longer.) However, I do sometimes pop the pods open. Not to remove the peas ... I prefer to leave them attached to the inside of the pod until they detach themselves naturally ... but just to keep them well ventilated. I started doing this because I have had some go mouldy on the inside of the pod, which spoils the peas. The other reason is the dreaded pea moth. It's not at all unusual for these maggoty little blighters to pop their heads out of peas shortly after harvest. One of the signs of their presence is a brownish patch on the pea itself so it's a good idea to remove any peas which have brown patches. Once the grubs start to pupate they gnaw their way out of the pea, leaving a small round hole and a lot of brownish powdery debris. Do watch out for them because they are destructive little buggers and will often maraud their way through the whole pod.
Coloured threads tied around the flowers when I hand-pollinate them enable me to identify the different hybrids at harvest time.
If you're going to save the peas to plant next year, leave them until they are completely dry before bagging them up. The noise they make when (gently!) dropped against a hard surface is the easiest way to tell. They should land with a hard clack. Any hint of a dull thud is a sign of moisture.
However, if you're planning to plant them immediately you don't need to dry them out fully. You can plant them straight away, although I've personally had more success by drying them down at least partially before sowing them. I know it seems a bit pointless to waste time drying them out and then waste more time rehydrating them, but I assume some chemical change takes place because they seem much more willing to germinate from a dry or semi-dry state.
Why would you want to plant them straight away? It's sometimes possible to get two generations of a pea crop into a single British season. Unlike things like peppers and tomatoes, which need a complete seasonal cycle to do their stuff and are sensitive to changes in day length, peas complete their business within a short and fairly standard timeframe regardless of what time of year they're sown, as long as the weather doesn't mess them up. In the UK, a crop sown in late February or early March can produce seed by the end of June which can be sown straight away for a crop around September or early October. Some varieties do better at this than others, and there's always a risk of sudden bad weather causing problems ... so it's probably only worth doing if you're an impatient plant breeder like me, wanting to grow out the F1 generation as quickly as possible so I can get on to the far more interesting F2 generation.