You can prevent cross-pollination using three main methods. Distance keeps plants far enough apart that pollen can't travel between them. Barriers block insects and wind from moving pollen around. Timing means growing different varieties in separate seasons so they never flower at the same time.
The isolation distance seeds need depends on how each plant spreads its pollen. Self-pollinating crops like tomatoes only need about 10 feet (3 meters) of space. Their flowers close up and do the job on their own. Peppers need 300-1,600 feet (91-488 meters) because bees carry pollen between plants.
Wind-pollinated crops need the most distance by far. Corn pollen can travel on the breeze for 2 miles (3.2 kilometers) or more. Beets and spinach send up light pollen that floats just as far. Most home gardeners can't keep these crops pure without barriers or timing tricks.
Cucurbits like squash, pumpkins, and cucumbers cross with each other over long distances too. You need about half a mile (805 meters) between varieties to keep them pure. That's why I use barriers to prevent cross-pollination when I grow multiple squash types in my small backyard garden.
In my experience with row covers, you want to put them over squash plants early in the season. This keeps bees away from your flowers. Then you hand pollinate each morning before the sun gets hot. I tested this method with three squash varieties in a space smaller than most parking spots. My seeds come out pure every time I save them.
Hand pollination techniques work great for crops with large flowers you can reach. You pick a male flower and rub its pollen onto the female flower. Then you tape or bag the female flower closed so no bees can visit it later. The fruit that grows will have pure seeds from only that one cross.
Bagging works even better for some gardeners. You cover flower buds before they open with small mesh bags. The flowers pollinate themselves inside the bag. Once you see fruit forming you can remove the bag and label that fruit for seed saving. This method takes less daily work than hand pollination.
The simplest solution for small gardens is growing just one variety of each cross-pollinating species. Pick your favorite zucchini and grow only that one. Choose one cucumber variety and stick with it. You won't need barriers or worry about distance at all with this approach.
I keep a chart on my shed wall showing what I'm growing for seed each year. This helps me track which crops need space from neighbors and which ones I can grow close together. Planning ahead saves you from finding out your squash crossed only after you plant next year's seeds.
Maintaining seed purity takes some effort but gets easier with practice. Start with self-pollinating crops like tomatoes and beans that need little isolation. Move on to hand pollination when you feel ready for more challenge. You'll build a collection of pure seeds that grow true year after year.
When I first started, I made the mistake of growing butternut squash next to acorn squash. The seeds I saved grew into strange fruits that tasted bitter. Now I plan my garden layout in winter to prevent cross-pollination problems before they happen. You can do the same by making a simple chart of what goes where each season.
Read the full article: How to Save Seeds: A Complete Guide
