11 December 2009
All higher plants, and that’s just about anything other than mosses, algae and what not, require some sort of fertilization to produce seed. Sometimes, as in the case of beans, this is self-pollination. But most other plants “out-cross” or must have pollen from another plant to set viable seed. This is accomplished one of two ways, by either insect or wind pollination.
Most horticultural crops of value to the home gardener are insect pollinated. This is true of many crops that are typically harvested when immature like cauliflower. Others require pollination to set fruit like tomatoes or peppers .
Honeybees are the most commonly recognized type of insect pollinator, though other types of native bees are also present in the urban environment. Some plants, such as those in greenhouses are pollinated by bumblebees.
Crops that attract insect pollinators usually have strong odors or showy flowers. Brassicas (aka cole crops such as broccoli, arugula and mustards) are a good example of this, with their characteristic 5-petal flower structure. Colours are a dead give-away of a morphology that attracts insects, but some larger and less colourful flowers are attractive in the polarized light that honeybees see in.
While bees typically have a range of up to 1 mile in rural settings, their range is somewhat limited in urban areas, as their flyways are somewhat disrupted by heavy traffic patterns. Keeping flowers blooming throughout the season (and especially early in the season) keep bees coming around for increased pollination success, even in these limited ranges. Most SE Portland neighbourhoods have at least someone keeping bees to assist.
This is important because insects are able to carry pollen from one plant to another, whether you like it or not. If you can keep them in or out of crops with a reasonable degree of certainty, you can get pure varieties of Open Pollinated (OP) seed.
Wind pollination is favoured by plants, such as wheat, hemp, sugar and maize. They all produce plain (though sometimes significant) male structures, which carry a massive amount of very light pollen that is easily carried aloft. Pollen from grasses such as wheat can travel up to 50 miles per day in strong Mid-western winds.
Most agronomic (traded as commodities, such as wheat and soybean) are wind- or self-pollinated. However, only a very few of the more common horticultural crops are. Among them are annuals like sweet corn and perennials such grapes and nuts.
Implications of these factors
If the goal is to be reasonably sure of what sort of seed you’ll get in the end, you’ll want to know just what each pollen parent is likely to be. The plant that sets the seed is the female parent and wherever the pollen comes from will determine the male parent. Because the female parent is the only one we are quite certain of, that is the first variety listed in any cross such as ‘Early Jalapeno x Cherry Bomb F1’.
To get pure seed we will want to practice isolation between varieties. We can accomplish this by separating blossoms by space, time or barriers. By planting all the same vareity of a given out-crossing crop in a given area, for instance, you can increase your chances of getting the crosses you want within the genetic pool of your choosing.
With some wind pollinated crops, such as maize, male structures (tassels) are easily removed for the production of hybrid seed (that which is the result of an intentional cross between two highly inbred lines). Otherwise, wind pollinated crops such as grains are all maintained by distance, usually in rural areas and measures in miles.
The same is true with vegetable crops, and some are much easier to save in the urban environment of SE Portland than others. Beans, peas and other legumes pollinate themselves before the flowers ever open up, so they are always maintained as pure-lines. Crops that out-cross need to have the possibility of rogue pollen assessed and managed.
This can be done with careful selection of crops to bloom at different times or those that are in different plant families that won’t cross with each other. Sometimes netting or pollination bags are used to protect blossoms for very specific crosses or to prevent them.
The urban environment presents certain challenges. For instance, you can’t keep your next door neighbour from growing a different variety of cucumber. However, a walk around your neighbourhood will give you a good idea of who is growing what.
Growing somewhat unusual crops such as herbs and salad greens makes it less likely that someone will be growing a pollen compatible crop nearby. You can also grow some crops like lettuce blends that are meant to outcross with other items for a blend.
One problem with this is the possibility of outcrossing with wild relatives. This can be minimized by avoiding crops that almost always outcross with useless wild relatives (such as carrot) or by controlling nearby weeds (wild lettuce).
Seed saving is a long-practiced art that has been the domain of home gardeners for thousands of years. You can do it, too.