The 101 on Saving True-to-Type Seed
True-to-type seed carries the expected, desired characteristics and qualities of the parent plants. You plant a Criolla Sella pepper seed, you expect a Criolla Sella pepper plant to grow.
Understanding the following basic botanical facts helps you successfully save true-to-type seed.
- A seed is created through fertilization.
- Fertilization requires pollination.
- Pollination is the transfer of pollen from the male part of the flower to the female part of the flower.
- 1 grain of pollen = 1 seed.
- A flower is either complete/perfect or incomplete/imperfect.
- Complete/perfect flowers have both male and female parts in one blossom.
- Incomplete/imperfect blossoms have either male or female parts but not both.
- Plants are grouped scientifically according to their physical and genetic similarities.
- Plants have long scientific names based on their scientific groups.
- Plants belong to large groupings called families. A smaller group within a family is a genus; still smaller is the species group.
- Gardeners commonly use a plant's variety name.
- Fertilization occurs between plants in the same species group, not across species groups.
- Plants with annual life cycles grow from seed, produce their own seeds and die all within one growing season. Biennials take two seasons to complete their life cycle.
The key to saving true-to-type seeds is knowing the plant's species. If varieties do not share the same species, cross-contamination of pollen will not happen. The seeds they produce are true-to-type.
If varieties share the same species, know the flower type and means of pollination to understand how to harvest true-to-type seeds.
- The flower structure of beans, peas, and tomatoes means they need very little intervention to keep seeds true-to-type.
- The more open nature of pepper flowers means a little more effort, such as bagging the blossoms, is needed to prevent unwanted cross-pollination.
- Due to the flower structure of the squash family (winter squash, summer squash, cucumbers, melons, watermelon, gourds) there is a great chance of cross-contamination. Seed savers use techniques such as hand-pollination and isolation by distance to harvest true-to-type seeds.
- Wind pollinated crops such as corn also require intervention to maintain seed purity.
Life cycle is primarily a matter of scheduling – the time required for harvest of mature seeds. Biennial root crops require over-wintering in storage in northern gardens.
The Squash Family
Remember, cross-pollination happens at the species level. It happens within a same species level, not between species.
A plant labeled C. pepo "Thelma Sanders" is one variety that belongs to the genus Cucurbita (C.) and the species pepo. A species can have many, many different individual varieties.
You can "safely" grow 1 plant variety from each of the 4 common domestic squash species (Cucurbita argyrosperma, C. maxima, C. moschata, and C. pepo) next to a watermelon (Citrullus lanatus), next to a cucumber (Cucumis sativus), next to a melon (Cucumis melo). Those 7 varieties will not cross-pollinate. They do not share a species level.
Now keep in mind that squash blossoms are imperfect, either male or female. "Help" is needed to move the pollen from one to the other for successful seed set. In nature, pollinators, typically bugs, are the helpers. This means when your neighbor grows a different set of 7 varieties, cross-pollination can happen if a pollinator goes between the two gardens.
The Cabbage Family
What makes the cabbage family challenging for seed savers is that one species is represented by seven different crop types. Cabbage, kale, cauliflower, Brussels sprouts, kohlrabi, collards and broccoli are all Brassica oleracea. Additionally, these crops are biennials. Most small-scale seed savers only allow one Brassica to flower at a time.
An Important Note
Despite all our intentions, there is always the chance that Mother Nature decides to counter-act our efforts to keep seeds true-to-type.
The following PDFs by groups such as Seeds of Diversity, Seed Savers Exchange and Organic Seed Alliance are great, easy to understand resources to assist your seed saving efforts.
These files are in PDF format which requires a reader; if you need one you can download Adobe Acrobat here.
Micro Seed Banking Primer - Seeds of Diversity - describes proper seed storage