Flower heads should be dried up. Let the seed and seed pods dry on the plants, and some will just shake off.
» Remove the seeds and put them in an envelope or baggy and store in your basement or freezer. You want them to stay dry, and it’s too humid in the refrigerator.
» A dry, sunny day is best to collect seeds because they’ll contain less moisture.
» If you’re collecting the seeds from several plants, make sure to label the envelopes as you go so there’s no confusion later.
» Tomato seeds have a special coating that keeps them from germinating. To remove it, put the pulp and seeds in a container with a little water and let the mixture sit a few days while it molds over and ferments. Then dump the seeds in a sieve, rinse, transfer to a paper towel to dry and then store.
» You don’t have to freeze seeds — a dark, dry basement or cabinet will work — but Porter says the survival rate will be higher if you do. To ensure that moisture doesn’t rot the seeds, put them in an envelope first and then put the packets in an air-tight plastic bag.
» Some plants will self-seed, especially herbs such as dill and fennel. Some gardeners just toss seeds in a bed in the fall, and while some will come up in the spring, some will rot in the winter dampness.