Whoops

Hmmm, something tells me these white runner beans have got crossed.

My neighbour asked me "D'yer want some o' them white runner beans?" meaning the ones he was growing last year. I wasn't planning to grow any runners this year but I don't like to turn down the offer of home-saved seed, because I can always horde it or pass it on to someone else. I was intrigued when I saw what he had though, because some of the white beans were black. And he'd harvested them all from his White Emergo plants. Clearly some had been fathered by the Black Magic crop I grew last year, despite my attempts to use a large jasmine hedge as a barrier. And there were some other beans which were a more conventional black and purple mottled type, presumably cross-pollinated with another variety growing in someone else's garden. He was going to pick out the white ones for me but I said I'd be happy to take some of the funny coloured ones too.

It's a strange quirk of some vegetables such as beans and sweetcorn that a cross-pollination can show up in the colour of the seed coat. With most plants, you won't find out about an accidental cross until you grow the next generation of plants. But where beans of different colours are grown together, individual beans that come out the 'wrong' colour are a sure sign of cross-pollination. A cross won't always show up in the seed colour though, so it's not a foolproof way to check the purity. In other words, black beans appearing in the pods of a white-seeded plant are a sure sign of an accidental cross with a black-seeded plant. But that doesn't mean for sure that the white beans aren't cross-pollinated. They may or may not be.

I collected a number of seeds from my black-seeded plants and they were all perfectly black, but the likelihood is that some of them will have been crossed with the white variety. The fact that there are no white seeds among my black ones doesn't necessarily mean anything, other than that the black colour is probably dominant.

Luckily none of this matters very much. My neighbour really doesn't care what variety of runner bean he grows, he just wants runner beans. The accidental crosses are technically F1 hybrids so they may even show a bit of extra vigour if he's lucky. And although I normally try to keep my varieties pure so that I can save their seed, I wasn't bothered too much about my Black Magic runner beans because I knew it was not going to be possible to isolate them from the crop next door. Runner beans cross so readily, it was inevitable that if we grew the same crop in adjacent gardens we would get crosses. If I'd really wanted to be sure of getting some pure seeds from my plants I could easily have resolved this by putting a bag over a few flower clusters to keep the bees out, and saving seed only from those. But I wasn't very impressed with Black Magic anyway so I didn't bother.

Fortunately for me, my neighbour's vegetable growing doesn't clash with mine very often. Most of the things I want to save seed from are things which normally self-pollinate (like tomatoes, peas and French beans) or which wouldn't normally be flowering if grown purely as a vegetable crop (like beetroot, carrots and onions). And most are things my neighbour doesn't grow anyway, as he has quite a narrow range of things he likes. The neighbour on the other side of me doesn't do any gardening at all, so there's no risk of cross-pollination from there.

Meanwhile I've been having to think about cross-pollination issues within my own garden. I've been planting out my special peas. These are mostly from the Heritage Seed Library, and are rare varieties which are not available to buy, and of which I've only got tiny quantities ... four to eight plants of each. The obvious thing to do would be to put up a nice sturdy trellis and plant them all together, but I can't do that. I need to save pure seed from all these varieties, and so I have to be as sure as I reasonably can be that they don't cross-pollinate. Accidental crosses between peas are not very common ... unlike runner beans, peas are designed to self-pollinate and their flowers are sealed so that insects can't normally get to the reproductive parts. But even with self-pollinators, there is always some risk of crossing. How big that risk is in your own garden can only be found out by trial and error because it depends on environmental factors such as local populations of insects. As I have an organic garden full of plant diversity, the pollinating insects are likely to be more abundant than they would be in, say, a conventional farmer's field. And as I can't readily replace these pea seeds if I screw them up, I have to be extra careful.

So ... I spent all day yesterday making small individual wigwams and twiggy structures for them all in different spots all over the garden, so that all of them are at least 10 or 15 feet away from any other pea varieties. Because I don't have that huge a garden it's not possible to separate them any further than that, so it'll have to do. If I have a cross-pollination disaster I'll have to rethink my strategy completely for next year. But hopefully they'll be fine. It was a lot of work though to plant them all at individual stations like this.

And it also makes conventional ideas of crop rotation pretty meaningless in my garden. All my crops are spread out and jumbled up with a bit of this here and a bit of that over there. So I don't bother with rotation, other than trying to be vaguely conscious of what grew in a particular spot last year and doing my best to mix things up. Crop rotation is a practice which goes hand in hand with monoculture. When you fill an area with large amounts of the same crop, pests and diseases soon become a problem. That's because areas of just one kind of plant goes against nature's way of doing things, and the result is an imbalance. The more diversity you have in your garden, and the more you blend different crops together and interplant with other things, the less of an issue it is. Diversity enables the garden to find its own balance in which pests exist but rarely reach problematic levels. I'm a great believer in trying to make use of nature's tides and balances rather than fighting against them. So I don't practice crop rotation as such because it makes more sense in my garden to avoid the need for it in the first place.

And of course the other advantage of garden biodiversity is that it gives you an excuse to buy loads of seeds. Heehee.

A seed saver's guide

Since we're getting into that time of year again, I thought it might be useful to put together a quick and simple guide to vegetable seed saving, since this sort of info is rarely found in gardening books. Most things can be home-saved, and it not only saves money but helps to maintain long-term biodiversity. As more and more traditional open-pollinated varieties disappear from the catalogues to be replaced by overpriced and overhyped hybrids, you could find yourself looking after a variety that's no longer available and helping to keep it from extinction. Like the lovely maroon and white beans shown above, an heirloom variety which is unavailable to buy.

When you save seed from year to year though, things can get more complicated. If you've read my post about F1 hybrids you may remember that plants fall into two basic types when it comes to reproducing. Inbreeders are happy to self-pollinate to kingdom come and show no ill-effects from it. Seed from a single plant, or even a single pod, can be enough to keep the variety going. Outbreeders are designed to cross-pollinate with other plants and need lots of genetic diversity. Without it they succumb to inbreeding depression ... within a few generations they start to lose their health and vigour. To avoid this you need to save seed from a number of plants, not just one or two. They will also often cross-pollinate with other compatible plants growing nearby so if you want to keep a variety true from seed you may need to isolate them from other similar crops.

So isn't it more hassle than it's worth to save seed from outbreeding crops? Not really, no. Because over the years you'll be selecting seed from the plants which grow best in your garden, and will gradually develop your own sub-strain which is optimised for your growing conditions. For this reason home-saved seed often does better than the stuff you buy (in America, commercial seed may have originated in a different zone with very different conditions ... while most seed sold in the UK is not produced in the UK at all).

F1 hybrid plants sometimes produce sterile seed, or no seed at all. And when they do produce viable seed it doesn't come true to type. The usual advice is not to save seed from F1 hybrids. If you're interested in plant breeding though, or just enjoy the element of surprise, you can ignore that advice. The resulting plants may turn out nothing like the parents, and may initially be inferior, but you'll have all sorts of brand new and possibly unique genetic combinations to choose from, and you're a step closer to producing a new open-pollinated variety.

Storage of seed is a whole subject in itself, but for year-to-year seed saving (as opposed to long-term storage) you can just dry them out as much as you can and store them in paper envelopes. I usually place each envelope inside a self-seal bag too.

OK, here we go:

Beans, French
Leave the pods on the vines for as long as possible, until they are dry or at least until they start to change colour. Then harvest them and dry them out further indoors. To hasten drying you can split the pods open, but try to leave the beans attached. When the pods are dry and brittle, shell out the beans.

Pollination issues: Strongly inbreeding and self-pollinating, so you can save seed from a small number of plants and grow different varieties close together with no problems.

Beans, Runner
Same method as for French beans.

Pollination issues: A rampant cross-pollinator, so keeping varieties true to type is almost impossible on allotments and where neighbours are growing them. If you need to keep them pure, hand-pollinate and bag up individual flower clusters to keep the bees out. If you're not bothered by a bit of genetic diversity though, don't worry about it.

Beetroot and chard
Beets and chards are biennial and normally go to seed in their second year. The seeds grow on long straggly spikes and take ages to mature. You can pick them off individually as they turn brown, or wait until they're nearly all brown, cut the whole spikes and run a gloved hand along them.

Pollination issues: Strongly outbreeding ... grow at least 16 plants to keep a healthy diversity. Beetroot, chard and leaf beet will all cross-pollinate with each other! To avoid this, grow only one type for seed at any one time. The pollen can travel up to five miles, so if purity is essential you'll need to bag up individual flower spikes.

Brassicas
Not the easiest to save for seed. Most flower in the second season. The long thin seed pods fall to bits very readily when they're ripe, and are likely to be ransacked by birds. The easiest solution is to cut the flower stalks as soon as they reach maturity and hang them upsidedown indoors with a paper bag over them to catch the little round seeds as they fall from the pods.

Pollination issues: Strongly outbreeding ... most can't self-pollinate and are prone to inbreeding depression. You really need to grow around 20 plants, if you have the space. They also cross-pollinate like mad, so isolation is needed to keep varieties true.

Garlic
Garlic is a plant that no longer bothers to set seed in the conventional sense. It's normally propagated by dividing and replanting the cloves. Save healthy bulbs from the regular harvest and leave them intact until planting time (autumn).

If you allow garlic to flower it will produce a huge number of bulbils in the flower head instead of seed. These are essentially miniature cloves and can be saved for planting. They take two years to produce full-size bulbs, but have the advantage that they're less likely to carry diseases. Cross-pollination is not an issue because the bulbils are produced asexually and are therefore genetically identical to the parent plant.

Lettuce
Seeds produce little white tufts, like thistles, when they're mature. They tend to mature at different times, so collect them regularly as they ripen. Allow them to dry indoors until very brittle then rub off and remove the fluffy tufts.

Pollination issues: Inbreeding. Seed can be saved from just one or two plants. They don't usually cross-pollinate, but to be on the safe side grow different varieties a few feet apart.

Onions and leeks
Flowering in the second year, onions and leeks produce beautiful spherical seedheads. Allow them to ripen until the seed capsules start to go pale and papery (they will probably all mature at different times), then cut the flower head and hang it upsidedown in a paper bag in a dry place.

Pollination issues: Strongly outbreeding, and need plenty of pollination partners ... try to grow at least 16 plants. Onions and leeks will readily cross-pollinate with others of their own type but not with each other, though onions may cross with shallots. To maintain pure varieties grow only one type for seed at any one time (you can still grow other varieties for eating, since those won't be flowering).

Peas
Same as for beans really; allow the pods to dry for as long as possible on the plant and shell them out when the pods are brown and crisp.

Pollination issues: Strongly inbreeding, so there are no problems with saving seed from just a few pods, and they're unlikely to cross-pollinate even when grown close together.

Potatoes
To save tubers for next year's crop, select them at harvest time and keep them in a cool, dark, frost-free place over winter. Select only firm and healthy tubers, which ideally should be about the size of a hen's egg. Leave them in a bright sunny place for a few days before storing them, which helps to toughen the skins and keep them dormant. Check them from time to time over the winter and chuck out any that are going soft or mouldy.

Some potato varieties will set top fruit which contain true seeds, and these can be saved too. If your plants have produced "apples", collect them when they're just starting to soften and are ready to drop from the plant. Process them in the same way as tomatoes (though the stinky fermentation process shouldn't be necessary ... just wash them thoroughly in a sieve to remove the pulp).

Pollination issues: Potato flowers cross-pollinate fairly readily, but in practice so few of them produce viable pollen it's unlikely to be an issue. Even when self-pollinated though, they will not come true from seed (because they have a slightly eccentric arrangement of chromosomes). Each one you plant will be effectively a new variety. Conversely, plants grown from tubers are genetically identical to the parent plant.

Squash (pumpkins, marrows etc)
The seeds are so huge you can't miss 'em. It's usually best to leave the fruits to ripen for a few weeks after harvest before collecting the seeds, or just leave them until you're cutting them up for eating. Wash the seeds to remove bits of pulp and fibre, then spread them out on a plate to dry thoroughly.

Pollination issues: Outbreeding, and will cross-pollinate with any other squash of the same species. Unlike most outbreeders though, it's not prone to inbreeding depression ... so you can get away with saving seed from just a few plants ... 6 or so will do.

Sweetcorn
Saving seed from sweetcorn is not really practical unless you have room to grow a lot of it!

Leave the cob (ear) on the plant for as long as possible or harvest when it's mature and bring it indoors to dry. When it's completely dry, the kernels can be removed by rubbing two cobs together.

Pollination issues: Extremely outbreeding! More prone to inbreeding depression than just about any other vegetable, and even sowing just one generation of inbred plants can result in an inferior crop. To be sure of maintaining health and vigour you need to grow and keep seeds from about 200 plants. Gulp.

Sweetcorn is wind-pollinated and produces stupendous amounts of pollen which is then cast to the four winds. To keep a variety pure it needs to be isolated from other varieties by some considerable distance.

Tomatoes
The 'proper' way to save tomato seeds is to scrape the seeds (including the gooey gel stuff) from ripe fruits into a small container, maybe add a tiny splosh of water, and leave it to ferment for a few days. During this time it will produce a crust of disgusting mould and a stench which could put you off tomatoes for life. When all the gel has dissolved away, rinse the seeds thoroughly in a sieve under running water and then leave them to dry for several days. Stir them around regularly to prevent them sticking together.

An alternative and much less stinky method is to scrape the seeds out onto a sheet of kitchen roll, spread them out to separate them and leave them to dry. The gel acts as a glue and sticks them to the sheet. I've heard this method criticised because the gel also acts as a germination inhibitor ... but in my experience the seeds germinate fine, even after several years.

Pollination issues: Strongly inbreeding. Saving a single fruit is enough, although more is better. Cross-pollination can happen but usually doesn't. If you want to be sure of pure varieties, isolate the plants from other types as far as you can.

Tomato cross-pollination issues

I'm currently writing up an article about making your own tomato hybrids, and I'm just going off on a related detour for a moment.

There's a lot of conflicting information about how readily tomatoes naturally cross-pollinate. Some gardeners swear they never do, while others report getting weird hybrids showing up when they least expect it. I've even bought a packet of baby cherry tomatoes from a major seed catalogue and had them grow into beefsteak-style monsters. Tomatoes are essentially inbreeders and have no biological imperative to cross-pollinate, but clearly they sometimes do.

Well, in the last few weeks I've spent a lot of time on my hands and knees staring into tomato flowers, and I think I can see how a lot of the confusion arises. Tomato flowers may appear pretty similar ... those little yellow cones and star-like petals are much of a muchness. But once you start peering at them closely, and more importantly, taking them apart ... you find there's a heck of a lot of diversity between varieties which potentially affects their pollination habits. And not only does it vary between varieties, it may affect them differently from garden to garden and with the weather and a whole lot of other factors. Which would explain the reams of conflicting information about whether/how tomatoes cross.

Big elongated green sepals are a quirky feature of Tangella flowers, whose buds look like tiny curled stars

Tomato flowers all have the same basic structure. The yellow cone in the centre is made up of anthers which are fused together. In most cases the cone is sealed all round so that insects can't get in, and the pollen is shed on the inside. Under normal circumstances the pollen falls straight onto the stigma (which is enclosed inside the cone) without ever coming into contact with the outside world. And that's why tomatoes rarely cross-pollinate.

But ... sometimes they can. These are the observations I've made on my own plants ... pollinator activity varies hugely from garden to garden.

Tangella, as I've mentioned before, has oddly structured flowers. The sepals are curled over backwards even in the earliest bud stage, and as the flowers develop the sepals remain hugely longer than the petals. On the inside though, the reproductive bits of the flower are pretty normal and average. It's a nice easy one to hand-pollinate because the pistil is large and the stigma very obvious when it's receptive. But the curliness isn't just in the sepals; the anther cone also curls outwards at the very tip, and that creates a small hole, big enough for a small insect to get inside. So although the pistil is short enough that it remains just inside the cone and may not be reachable by bees, it could theoretically be pollinated by something else.

Clementine has smaller paler flowers than average which grow in unbelievably massive trusses. The anther cones are compact and stay tightly closed, so self-pollination is assured. But ... unlike all the other tomatoes I'm growing, Clementine attracts bees. Particularly bumble bees. They don't get a lot of joy out of it because the flowers are tight shut and I've had a few amused moments watching them desperately paddling their legs on the petals trying to get in. But they keep coming back, and if they really want to get at the pollen they may bite their way through the anther cone, which would be the first step towards cross-pollinated tomatoes.

Black Plum produces quite generous amounts of pollen, even in cool weather. It has an anther cone which is fairly open at the end, and a pistil which is long enough that the stigma is flush with the tip of the cone and therefore accessible to pollinating insects. But in my garden the insects don't go near it. So I would say Black Plum is biologically more geared up for cross-pollinating than most tomatoes, but what with throwing so much of its own pollen around and lacking insect allure I think it's still most likely to self-pollinate. But in certain circumstances I could see it hybridising like mad.