Specific seed collecting tips follow on this page.
SEED SAVING INSTRUCTIONS - Cole Crops
Biennial seed saving. Isolate broccoli by 1 mile (5,200 feet) from all other Brassica oleracea. In fall remove plants from soil and pot them in sand. Store plants between 32-40° F. Transplant back outdoors in early spring and allow to bolt. Harvest seed pods when dry and clean by hand. - from Urban Farmer
SEED SAVING INSTRUCTIONS - SQUASH & PUMPKINS
-from International Seed Saving Institute
For the most optimal cucumber seed collection, select from only disease free plants which have the most flavorful fruit. Seed must be harvested when the fruit is mature, so allow the cucumber to languish on the vine past its eating stage – near the end of the growing season. Fruit will be orange or yellow when fully ripe and ready to pluck mature seeds from. In order to harvest seeds from fleshy fruits such as cukes or tomatoes, the wet method of removal should be applied. Remove the seeds and allow them to ferment in a bucket for three days with a small amount of warm water in order to remove the gel coating surrounding the seeds. Stir this concoction daily. This fermentation process kills viruses and separates the good seeds from the pulp and the bad seeds. The good seeds will sink to the bottom while the bad seeds and pulp float at the surface. Pour off the pulp, water, mold and bad seeds carefully after your three days have passed. Remove the good seed and spread them on a screen or on paper towels to dry thoroughly. Once completely dry, your seeds can be stored in envelopes or a glass jar with a clear label specifying the date and variety. Place the container in the freezer for two days to kill any residual pests and then store in a cool, dry place such as the refrigerator. Seed viability decreases over time, so be sure to use the seed within the next three years. - from Gardening Know How
Read more at Gardening Know How: Cucumber Seed Collection: Tips For Harvesting & Saving Seeds From Cucumber https://www.gardeningknowhow.com/edible/vegetables/cucumber/cucumber-seed-harvesting.htm
SEED SAVING INSTRUCTIONS - Grains
SEED SAVING INSTRUCTIONS - Okra
For okra seed harvesting, the seed pods must dry on the vine and beginning to crack or split. At that point, you can remove the pods and split or twist them. The seeds will come out easily, so keep a bowl nearby. Since no fleshy vegetable matter clings to the seeds, you don’t need to wash them. Instead, dry the seeds in the open air for a few days, then store them in an airtight jar in the refrigerator. Although some okra seeds can remain viable for up to four years, many do not. It’s best to use collected okra seeds the next growing season. For best results, soak the seeds in water for a day or two before planting.
Read more at Gardening Know How: Collecting Okra Seeds – How To Save Okra Seeds For Planting Later https://www.gardeningknowhow.com/edible/vegetables/okra/how-to-save-okra-seeds.htm
Onion seeds are not typically difficult to grow or to collect, but keep in mind that they are a biennial crop, meaning that they seed once every two years.
Life Cycle: Biennial
Recommended Isolation Distance: When saving seeds from onion, separate varieties by at least 800 feet up to ½ mile. To produce seed from onion, select as many perfect onions as you can spare for seed production and store them through winter in a cool, dry, dark place. Replant them in early spring at the same bulb depth and spacing as when they were harvested.
Recommended Population Sizes: To ensure viable seeds, save seeds from at least 5 plants. To maintain a variety over time, save seeds from between 20-50 plants.
Assessing Seed Maturity: Watch first for flowers and then for seed heads to form during the late summer of the second season. Wait for the seed heads to dry. Most of the flowers will be dry, and the seeds will begin to fall out on their own.
Harvesting: After the plants bloom and seed heads begin to dry, gather the heads in a paper bag. Most of the seeds will fall out on their own; shake the bag to free the remainder of the seeds.
Cleaning and Processing: Separate the seeds from the stems and other matter that makes up the seed head. Allow the seeds to air-dry for a few days before storing the seeds in a cool, dry place.
Storage and Viability: When stored in a cool, dark, dry place, onion seeds will remain viable for 2 years.
-from Seed Savers Exchange