Only Collect Seed From Open-Pollinated Varieties, Not Hybrids
When it comes to collecting seed it is important that you understand your plants and know the difference between open-pollinated, heritage plants that will come true from seed and hybrids that will not come true from seed. In other words, if you plant seeds from a hybrid, the plants that come up might not look anything like the parent plant. Collect seeds from plants that you know should come true from seed.
Understand That Pollination is Essential to Viable Seed
The simple fact of the matter is that many plants need pollination to have occurred in order to make viable seeds that will grow the following year. It is not always easy to tell whether this has occurred. For this reason, those who depend on their gardens will usually test the viability of a batch of seeds at some point before the spring.
Consider Cross-Pollination
Remember that cross-pollination can occur between many of the plants we commonly grow in our gardens. Members of the brassica family with cross-pollinate, as will squash, pumpkins and other members of the same family. It is not always feasible to separate plants by enough in a standard garden so if you do want to collect seeds you will have to use row covers and bags over certain plants to prevent cross-pollination.
Select Seeds From Plants With Good Traits
This is really rather obvious but you should always select seeds from plants that are thriving. You should pick seeds from a few of your best plants in order to get a reasonable gene pool for each type of plant you wish to grow next year. Selective seed gathering will ensure that the plants of each following year will be better and better suited to the specific conditions in your garden.
Make Sure Seed Is Totally Dry Before Storing
There is no point going to all the effort of collecting seeds if you then store them before they are fully dry. Doing so is a recipe for disaster as seeds that are not fully dry will rot or experience other problems and you may be left with no usable seed at all.