Plant Basics

Cross-pollinated plants are those in which pollen from one plant is needed to fertilize the flower of another. Important Note: self and cross-pollination are not two clearly distinct means of pollination. Rather, they are extremes along a continuum. So for example, some tomato varieties are mostly self-pollinated within each flower, with little or no crossing. Other tomato varieties, whose female flower parts extend beyond the protective flower, can be cross-pollinated by insects.

Open pollinated plants can be either self-pollinating or cross-pollinating plants. Open pollinated plants are those that are not hybrid and will produce seeds that will grow into plants just like the parent plants. It is only from open pollinated plants that gardeners can save pure seed!

Hybrid plants are those that are the result of the cross-pollination of two different varieties of parent plants (usually within the same species). This produces a new variety that is a genetic mixture of the two parent plants. However, the seeds produced by the new hybrid plant will not reproduce the same hybrid plant, rather, the resulting plant can display any mixture of the features of the original parent plants. The hybrid plant can only be reliably reproduced by cross-pollinating the parent plants.

Heirloom vegetables are those that are non-hybrid and have been saved and passed on for many generations. The word heirloom is sometimes used interchangeably with open pollinated.

Family, genus, species, variety: It is important to know the botanical classification (the family, genus, and species) of each crop for which you would like to save seed because different varieties of crops within the same species have the ability to cross pollinate (See Family, Genus, Species handout). For example, all varieties of muskmelons, cantaloupes, and honeydew melons can cross-pollinate because they are of the same family (Cucurbitaceae), genus (cucumis), and species (melo). However, cucumbers will not cross-pollinate with these melons, even though the family and genus are the same (Cucurbitaceae, cucumis), because the species (sativus) is different. But all different varieties of cucumbers can cross-pollinate.

Flower Structure

Maintaining Varietal Purity

Why is it important, when you are saving seeds, that different varieties do not cross-pollinate? Well, I am growing two types of cucumber that I really like. One is Suhyo Long, an open-pollinated Asian cucumber that is dark green, narrow and long, with bumpy skin. The other is Boothby’s Blonde, who’s fruit is squat and thick, oval in shape, smooth skinned and cream to rich yellow orange in color. If I grow these two types of cucumber near each other, and save seed without making sure that they don’t share pollen, then the plants I grow next year might exhibit any combination of the genes of the two types. I might get a short, squat dark green bumpy skinned cucumber, a long yellow one, or any interesting variation in between! Cross-pollination of different varieties and selection and saving of the most desirable new varieties that emerge is how an amazing diversity of great vegetables has evolved over thousands of years. But, if we do not carefully save the varieties we already have (maintain their varietal purity) those may disappear forever.

Isolation by Distance. By growing different varieties of the same crop species far enough away from each other that insects or wind cannot introduce pollen from one variety to the other, you can save pure seed. The necessary distance, the Isolation Distance, varies according to plant species, but is usually at least _ mile or more. This means that you would have to be aware of any other crops of the same species being grown in a quarter mile (or larger) radius from your own garden. This is often very difficult for home and community gardeners to know. The required isolation distance can be reduced if physical barriers, such as tree or hedge borders or buildings effectively block pollen travel.

Isolation by Time. You can save pure seed if different varieties of the same species flower at different times. The first variety to flower would have to stop flowering and set seed before the next variety reached its flowering stage. Time isolation, however still requires knowledge of any other crops of the same species being grown within the isolation distance.

Mechanical Isolation: Hand Pollination, Bagging, and Caging. Mechanical isolation refers to creating a deliberate physical barrier to pollen transfer between varieties within the same species.

Hand Pollination. This is mainly used for insect pollinated crops. It involves daily careful inspection of the flowers on plants from which you wish to save seed. For plants with separate male and female flowers, such as summer squash and cucumbers, in the evening, identify male and female flowers that will open the next day, and tape them shut. You will want to tape 4 ­5 male flowers per female flower. In the morning, remove the male flowers from the plants, remove the flower petals from 4-5 of the male flowers, carefully unseal one female flower, and gently brush pollen from the male flowers onto the receptive female flower organ, then quickly tape the female flower shut again, to exclude any insects. Mark the female flower with some brightly colored cloth, yarn, or plastic, and make sure that everyone who frequents your garden to harvest knows not to harvest the marked fruit! Repeat the above process for each female flower.

Bagging. Bagging is the covering of the individual flower or flower cluster with a bag (made of paper or lightweight cloth, but never plastic because plastic will trap moisture and heat and destroy the flower), in order to exclude unwanted pollen. This is most often useful with self-pollinating plants (but is also used for corn, a wind-blown cross-pollinator). It is important that the bag create a good seal around the flower stem to exclude pollinating insects. Winding cotton around the stem before securing the bag is useful. The Bag can be removed once adequate time has been given for the flower to self-pollinate and begin setting fruit. Once the bag is removed, mark the stem of the developing fruit, as above.

Caging. Caging is done by erecting a cage over multiple plants of the same variety. These cages can be relatively easily home-crafted, with a frame made of wood, plastic or metal piping, and covered with window screen or a special agricultural fabric (known as reemay or floating row cover) which is light enough to allow light and water to pass through, but not insects.

Caging is useful for some self-pollinating plants, like peppers which can be as much as 80% insect pollinated. In this case, the cage is used to exclude unwanted insect pollinators that might introduce pollen from other varieties.

Alternate day caging can be used to save pure seed on two cross-pollinated varieties of the same crop species that flower at the same time. You must have enough cages and large enough to cover all of the plants of both varieties. One variety is left uncaged on one day, allowing pollinating insects to visit and pollinate. The next day the other variety is left uncaged. The drawbacks of this method are that plants have much less exposure time to pollinating insects and therefore fruit set will be diminished. Also, this will only work if the gardener knows that no other crops of the same species are being grown and in their flowering stage within the necessary isolation distance.

Caging with introduced pollinators can be used to save pure seed on any number of different insect pollinated, cross-pollinated plants in the same garden. To ensure adequate genetic variety, a minimum of six but preferably more plants of the same variety would be caged together. The difficulty is in introducing the insect pollinators. Trapped honeybees will most often spend their time trying to find an escape from the cage and do little or no pollinating. Flies can also be trapped and introduced to the cage, but not all plants are effectively pollinated by flies, and even for those that are, pollination may be low. This technique is most often used by professional seed savers who have special cages with bee hives built into the sides.

Plant Selection Criteria and Population Size

Population Size. In cross pollinating crops, maintaining a high degree of genetic diversity within each variety that you save is very important to the overall health of the crop. Genetic diversity is what makes it possible for cross-pollinated plants to respond and adapt to positive and negative environmental conditions, to co-evolve in a place, over time, with pests, diseases, climate, water availability, etc, and remain strong. Often, saving of seed from six plants of each variety is recommended as an absolute minimum, with larger numbers more desirable.

Self-pollinated crops, particularly those that are not susceptible to even a small amount of cross-pollination, like beans, are actually naturally inbred, with relatively little genetic diversity.

Seed Processing

Most seeds will have to be fermented to remove the jelly coating that keeps the seeds from germinating inside the fruit. Fermentation is a natural process that any fruit that is dropped to the ground and left to rot will go through. Fermentation prepares the seed for germination, and can also help kill any diseases that might otherwise pass from parent plant to the next generation. Let the seeds, pulp and juices sit in the bowl at room temperature, never in direct sun, for 3-4 days. Stir twice daily. Mold and a strong smell will develop, so it is preferable not to do this in your home. Adequate fermentation has occurred when you see bubbles rising through the liquid or the surface is totally covered in mold, at about the third day in warm temperatures, a little longer if it is cooler. It is important to remove the seeds from the mix before they should begin to germinate.

Add enough water to roughly double the volume of the mixture. Stir until the denser, viable seeds settle to the bottom of the bowl and the lighter, hollow seeds and other debris at the top can be carefully poured off. Add water and repeat until only viable seed remains. Pour the seeds into a tight mesh strainer, rinse in running water, then drip the strainer dry, wipe the bottom with a towel to remove as much water as possible. (Note: any cooking or eating bowls used for fermentation should be cleaned well and sterilized with a bleach solution before being used for food preparation again.)

Pour the cleaned seeds onto a glass or ceramic dish (paper, cloth, and plastic are difficult to remove seeds from once dry) or a horizontal window screen. Leave seeds in a dry environment with good air circulation and out of direct sun. Stir twice daily to get even drying and to keep seeds from sticking together.

Dry Processing, Threshing, and Winnowing. Dry processing is for plants, such as beans or broccoli, whose seeds are dry when mature. Individual seed pods can be picked from each plant as they dry and mature, or in damp climates or those with short growing seasons, the entire plant may need to be removed from the ground and hung in a dry place to continue the process of drying and maturing.

To remove seeds from seedpods, they are threshed- hit, smashed and broken until the seeds are freed. This can be done by placing dried seedpods in a clean pillowcase and jumping on it or hitting it with a board or stick. Some seeds are sensitive to too much pressure and can split or crack. You will learn by experience the right amount of pressure to use with different seeds.

Winnowing is the process of removing the chaff (bits of pods and other dry plant material) from the seeds after threshing has been done. This can be done using controlled wind, as from a box fan, to blow lighter weight chaff away from heavier seed as you pour seed and chaff from one bucket to another. Experiment with wind speed and distance from the fan until you are able to get mostly just seed to fall into the second bucket. Always do this on a tarp or sheet so you can recover any seed that doesn’t make it in to the second bucket. Always shake the sheet or tarp free of all debris before using it to winnow another type of seed.

Screen winnowing is another useful method. This involves using screen material, which can easily be gotten with 1/8, _, and _ inch mesh. Select a size that is large enough to let the seed pass through but that excludes much of the chaff. Once all of the seed has passed through, if there is still a lot of very small chaff, select a screen size that is too small for the seeds but lets the remaining chaff pass through it.

An easy gravity separation technique is also useful. Put seeds, already winnowed of larger chaff material, in a bowl. Swirl the contents and the heavier seeds will collect at the bottom and the lighter chaff at the top. Tip the bowl slightly and blow the chaff away. Repeat as long as necessary.

Seed Storage

To protect seeds from moisture, they should be kept in airtight storage containers. Small quantities of seed can be kept in paper or plastic bags, but these are not airtight, and must themselves be stored in an airtight container. Glass is the most commonly useful airtight material when lids are fitted with a good rubber seal. Glass canning jars, used baby food or other jars with rubber sealed lids work well. Glass jars without a rubber seal can be fashioned one out of tire inner tubes.