Peas: another whopping great post

Alderman, an old-fashioned tall pea, after summer rain

When I got my own garden for the first time nine years ago and started growing vegetables, I learned everything from The Vegetable Expert by Dr D.G. Hessayon. Published and endlessly reprinted in the 1980s, it's got to be the most ubiquitous veg-gardening book in the UK. I read it over and over again, so carefully that even now I can remember bits of it by heart. I used to follow its advice absolutely to the letter, sometimes successfully, sometimes not. It's still one of my most-used garden books and it's brilliant as a quick reference, but now, after a few years' experience, I more often than not find myself flinging my hands up in horror as I read it. It blithely recommends using all kinds of environmentally reprehensible products like peat and Chlorophos, and routinely sprinkling your soil with poisons to kill off pests before they even think about approaching your plants. I wouldn't dream of doing any of those things now. Many of the products recommended in the book have since been banned.

It's good to do things differently from what the books say sometimes, and flout the instructions on the seed packets. They're only given as general guides anyway, and it's only by experimentation that you find out what works or doesn't work in your garden. Don't be afraid to try things out just because the books tell you not to, or that it's better to do it some other way.

Over the years I've learned a few things about peas that differ from the received wisdom. I'm not an expert on pea growing. Far from it. I'm learning all the time. And I'm also still experimenting, because the more time I spend with peas the more I find much of the common knowledge about them is at best outdated and at worst misleading. For some reason, peas in particular seem rife with misunderstanding and non-information.

I think part of the problem is that once an idea is published it tends to get repeated and copied and passed around and nobody thinks to question it.

I remember seeing a tip about peas on that greatest of British institutions, BBC Gardener's World. Plant sweet peas in amongst your vegetable peas, a head gardener suggested, because the bees will be attracted to the scent and will pollinate your crop better. So I tried it, and it looked very lovely, but as soon as I'd planted it I thought - hang on ... unless I'm missing something, that's a complete misunderstanding of what peas do. You don't need to try to attract bees to them. Their flowers are sealed and enclosed. The male bits grow alongside the female bit inside a closed bag and dump their pollen all over it before the flowerbud has even opened. Super-efficient. No bees involved.

Growing sweet peas among your garden peas looks gorgeous but it won't make a sod of difference to pod set.

And another thing. These days I very rarely sow peas directly into the ground. For years I did, because that's what it says in the book and on most seed packets. But I invariably ended up wasting most of the seed as only a handful managed to survive long enough to grow into slug-ravaged stumps. Peas are hugely vulnerable to rotting in cold damp soil, and too much rain during the week after sowing can wreck a crop. Even if you're able to avoid that, the seeds are often gobbled up by mice or birds. And if they survive long enough to poke their heads above ground, the slugs and snails get 'em. In my garden, direct-sowing just doesn't work.

Baby peas in Rootrainers

So I generally start them off in modules indoors. It's more work than sowing direct, I admit, but the success rate for germination is many times higher. Like most leguminous crops they produce long roots which need space to develop freely, so it's best to sow them in deep open-ended pots. You can buy purpose-made "Rootrainers", which are deep modules with ridged sides designed to 'train' the roots straight downward. They're hinged at the base so that you can open them easily at transplant time with minimal root disturbance. They always seem to take ages to fill though and swallow up stupendous amounts of compost. They do work pretty well and are re-useable but I'm not absolutely convinced they justify their rather opportunistic-looking purchase price (around ten quid in the UK for what is essentially a pack of plastic flower pots).

Cheaper and in many ways just as good are the cardboard centres from toilet rolls. Lightly fill them with compost and stand them upright on a tray. They have the additional advantage that they're porous and retain moisture, which helps to keep the compost evenly moist between waterings, and as they're biodegradable they can be planted out just as they are without disturbing the roots at all. You can buy purpose-made biodegradable grow-tubes if you prefer, which work the same way and look less toilet-roll-like. Sow two or three peas in each tube. The key thing is to add water to the tray underneath and let them suck it up from below rather than watering from the top. That way they develop nice deep roots as they search for water and the compost around the seed itself stays relatively dry. The roots will quickly grow out of the bottom of the tube so it's important to keep them moist when they do.

Baby peas in bog rolls. This is a heritage variety, Ne Plus Ultra. And no I didn't choose that wallpaper.

"B-b-but..." I hear you say with a quivering lip, "what if I'm starting a large crop of peas and don't have the space or the time to sow them all in modules?" A good compromise is to pre-sprout the peas indoors before sowing them direct in the garden. Spread all the seeds out evenly between sheets of kitchen roll (I think that translates as paper towels in the US) and keep it well-plumped up with water but not so as it's floating. In a couple of days most of them will have developed small white shoots. You can then take them outdoors and sow them as normal. You will probably still get some losses but not as many as you would if you sowed unsprouted seed, and at least you won't have to wait three weeks for them to germinate in the cold ground.

There's a common misunderstanding that peas are frost tender. It does vary with different varieties and climates, with round-seeded varieties being hardier than wrinkle-seeded, but on the whole most peas cope well with spring freezes. The usual advice to delay sowing until the soil warms up in March is based on the assumption that you're sowing them directly (unsprouted) in the ground, because peas germinate so slowly and erratically in cold wet soil. So you can actually start them earlier than the packets suggest if you pre-sprout or sow in modules. With luck you can even plant them out before the slug and snail season has got underway, so the plants can establish themselves and the apical tip can grow beyond the snails' reach without being molested.

The most crucial thing if you want to get a decent crop is to encourage the plants to develop really good roots, as deep as possible, as quickly as possible. Which is why Rootrainers and bog-roll tubes are worth the extra hassle and compost. Adding some bone meal at planting time will benefit the roots, but any other kind of fertiliser may be counter-productive. What they do like though is a nice bit of organic matter dug into the soil. I use either leafmould or a spent mushroom compost made from horse manure. Another thing which I found made a huge difference was to apply a layer of the horse manure compost as a mulch around the pea plants once they've got established. Multi-benefits: it breaks down gradually and enriches the soil, it retains much-needed moisture around the roots and it stops a few weeks worth of weed growth, which is much appreciated later on when the plants are so big and tangly you can't weed around them anymore.

This is thought to be one of the pea varieties used by Mendel in his discovery of genetic laws in the 1860s, a yellow-podded beauty called Golden Sweet. The seeds come in many different shades and are speckled with purple.

And now for another nugget of pea wisdom I learned the hard way. My first vegetable plot was in the garden of a newly built house. The site had previously been a television factory, and before that it was a pig farm. It had never been a garden before. My first crop of peas failed dismally, and the second wasn't great either. I had no idea why.

It's fairly well known that peas and other legumes are able to accumulate and fix nitrogen through nodules on their roots. The usual advice is to leave the roots in the soil after harvesting, so that the root nodules biodegrade and release nitrogen to feed the next crop. What I didn't know, and only discovered in a post on Bifurcated Carrots last year, is that it doesn't just happen on its own. In order to perform this miraculous function peas need access to a specific soil bacterium called rhizobium, and although it builds up in the soil over time if you grow leguminous crops, it's not naturally present in useful amounts in 'virgin' soil. And without it, yields can be very low.

The relationship between pea plants and rhizobia is symbiotic. The bacteria can survive in the soil quite happily but can't start fixing nitrogen until they find a legume as a host. They 'infect' the plant by entering through the root hairs, and the plant responds by developing swollen nodules on the roots. The bacteria multiply rapidly within those nodules then set about transforming nitrogen from the atmosphere into a plant-usable form, effectively feeding the pea plant from within its own root system. In return for this free fertiliser the pea plant supplies the rhizobia with the oxygen they need, in the form of haemoglobin (which is why the nodules are sometimes red inside when you cut them open). If you want a nice clear explanation of the science involved, try here.

Because of their unusual nitrogen-fixing properties, peas don't need to be fed with conventional fertilisers or anything else high in nitrogen. As well as being harmful to the environment in excessive amounts, it encourages plants to produce masses of leafy growth which will attract pests, and fewer pods. The air is about 79% nitrogen so there's plenty of it about, but plants can't use it in this form. The beauty of rhizobia is that they convert that inaccessible nitrogen into a usable form, enabling peas to grow healthily without depleting the soil and without the need to add synthetic nitrogen compounds. In fact, growing them actively benefits the soil if their roots are left in the ground to biodegrade as a natural slow-release fertiliser for the next crop.

If peas have never been grown in the plot before, you need to use an inoculant to get them working their nitrogen magic. That means buying the appropriate strain of rhizobium (there are different ones for different legumes) and applying it at planting time, usually by mixing it into a paste and dipping the seeds in it before sowing. According to the University of Minnesota, who have a research programme on rhizobia and legumes, the use of an inoculant will often increase yields by around 30%.

I felt a bit of a chump for not knowing anything about this before. But when I started researching it I found a black hole of non-information, at least in the UK. It's a different story in the US ... you can buy rhizobium inoculants very cheaply from garden stores. Over here though they are non-existent. There appears to be only one inoculant product in the UK, with the brand name "Natures Nitrogen". However, in all my googling I've not been able to find a single supplier, nor any indication of its price. Clearly nobody in the UK inoculates their peas! There's no information about it in any of my gardening books either. It's a total blank.

Pink flowers and purple pods: Mr Bethell's Purple Podded

I'm perplexed by this situation, because it has significant environmental implications. For the last 60 years or so farmers here have been throwing artificial nitrogen products all over the land, causing algae blooms in ponds and streams which suffocate fish, harm other wildlife, and contaminate our drinking water. Growing leguminous crops with the help of rhizobia has the opposite effect; it utilises nitrogen from the air rather than the soil and contains it in a form that will not contaminate the soil or the groundwater. It also reduces the need for fertilising the subsequent crop, which has economic as well as environmental benefits. Unlike conventional nitrogen products, it's benign and sustainable.

Maybe once again it's a case of everybody doing it the way everybody else does it and not questioning whether or not there's a better way.

But anyway, as far as me and my tiny patch of land are concerned, I can't try rhizobium inoculation because I can't get it. So here's what I'm doing instead. I'm digging out some of the old root systems from last year's pea crops, mashing them up with a little soil and distributing them around other parts of the garden, specifically the areas where I haven't grown peas before, and digging them in with a sprinkle of seaweed meal. One of the things seaweed meal does is stimulate microbial activity in the soil, which I'm hoping will help the rhizobia to thrive as the nodules break down. I must emphasise though that this is just an experiment ... I have no idea whether or how well it will work.

Blimey, I didn't intend to write this much, but those are my tips for growing peas, anyway.

I would love to hear from you all about whether your pea flowers are visited by bees. I don't think I've ever seen them taking an interest in mine, but I'd be curious to know whether there are occasions when they do. Sometimes when bees are desperate they bite their way into flowers they can't normally get into, but that may or may not include peas. If you've ever had accidental cross-pollination with peas, I'd be interested to hear about that too.

Postscript: I've just found a UK supplier for "Natures Nitrogen". One of the seed companies in my recommended list, Seeds of Italy, are offering it at £1.25 a pop.

To summarise:
Peas are reasonably hardy. Germinate them indoors, harden off and plant out.
Sow them in deep modules and water them from the bottom.
Manure or compost dug in before planting will keep them happy all season.
Mulch the plants to conserve moisture and smother weeds.
Peas ideally need rhizobium bacteria, which are not always present.
Peas do not need nitrogen fertiliser.
Peas do not need bees or other pollinators.