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The first rule of seed-saving is that you must select “open-pollinated” vegetables such as heirlooms and not commercial hybrids. The hybrid does not reproduce fruits that are true to the parent plant. Learn more on our Seed-Saving 101 Guide.

But also even if plants are open-pollinated, some vegetable plants are very promiscuous and, with the help of insects or the wind, their pollen will travel between different plant varieties and mix up the genetics. The result is unintentional cross-breeding so that your seeds will not resemble the original vegetable. Ever seen a “Frankensquash” resulting from, say, a winter squash and pumpkin cross pollinating? It can be fun but you never know what you’ll get and the flavor is usually inferior.

It doesn’t affect this year’s fruit but if you plant those seeds next year, you will get a totally different outcome. To keep the strain pure, the vegetables need to be planted far apart from each other. How far is far enough? 

The amount of distance required between plants of different varieties depends mainly on the method of pollination and the life cycle of the plant.

Distance Between Tomato Plants

The seeds often saved by home gardeners are for those luscious heirloom tomatoes. Since they are annuals, mostly self-pollinated with only a little help from bumblebees buzzing the blossoms, tomatoes need to be 10 feet away from other tomato varieties to keep the plants from crossing. 

Beans, Peas, and Lettuce

Annuals that are self-pollinating like beans, peas, soybeans, and lettuce only need to be 10 to 20 feet away from another variety of bean, pea, lettuce or soybean to limit cross-pollination. This will insure that the seeds you save from your rattlesnake beans will produce rattlesnake beans next year and not lima beans or some mutant hybrid. 

Beans are actually one of the most reliable seeds to save because they can transfer pollen from male to female parts of the blossom before the flowers even open. If you grow just one variety of bean, pea or lettuce, you won’t have to be concerned that they might cross with another variety. 

I save seeds from my soybeans every year with great success since I grow only that one variety and don’t have to worry about it accidentally crossing with another one.

Peppers and Eggplants

Peppers are annuals that can be self-pollinated and insect pollinated. They recommend keeping varieties 300 to 1600 feet apart if you want to save their seeds. Same distance for eggplants and ground cherries. 

I save the seeds of ‘Thai Dragon’ peppers every year. Since we grow lots of other varieties of peppers I keep the dragon in a pot near the house—far away from the others in the garden—or, so I thought. Last year, the seeds we saved produced mutant peppers that looked more like pepperoncini but had the heat of ‘Thai Dragon’. Apparently those two weren’t kept far enough apart to prevent some horticultural hanky-panky. This year I am reaching way back in my seed supply to find some seeds that hopefully will give me the desired results, otherwise our favorite hot pepper will be lost forever!

Squash, Cucumbers, Melons

Members of the cucurbit family (melons, cukes, squash, pumpkins) are insect-pollinated annuals that need to be grown 800 feet to a half mile apart!

If you have tried saving the seeds from your favorite summer squash only to end up with fruit that is more like a tough-shelled gourd instead of a tender squash, it probably crossed with another plant of the same species like a pumpkin, gourd, or winter squash. 

Broccoli, Kale, and Brassicas

If you’re a beginner seed-saver, I don’t recommend seed-saving biennials. However, if you become a master seed-saver, note that biennials in the brassica family are also insect pollinated. A special broccoli or kale needs to be planted 800 feet to a half mile away from another variety of broccoli or kale. 

Beets, Swiss Chard, Spinach

If you think those distances are wide, other biennials such beets and Swiss chard, and annual spinach are wind pollinated and individual varieties need to be grown 800 feet to one mile apart!

How to Plant for Seed-Saving

Here’s the good news. You don’t need to own acres of land! You will only need to isolate 1 or 2 plants of each species that you intend to save seeds from, not the entire crop. Each plant usually generates a lot of seeds, enough for your family and to share with others. 

There are caging methods you can employ to isolate the plants but they require hand-pollination. Planting wind-pollinated plants in the lee of a building or tall fence may also help to prevent accidental cross-pollination. Growing only one variety of the species you want to save at a time can also help but it is hard to totally isolate them, especially if other gardens are nearby. Bees fly far and wide to find the pollen that they like.

A simple seed-saving garden plan

If you’re starting out, keep it simple. Stick to the four vegetables that are self-pollinating: tomatoes, beans, peas, and lettuce.  

Keep these seed-saving plants isolated from the rest of the garden which contains the vegetables that you plan to eat. The good news is that you can mix the seed-saving plants with each other in any way you wish. Simply plant in one long row if you wish.

Let’s say you’d like to save seeds from two different heirloom tomato plants. Just make sure that there is 10 feet between between the two varieties. If you plant in one row, plant seeds for beans, peas, and lettuce in between the two tomato varieties.

You can build more rows and stagger the same way. It may help to draw this out on paper or create a small chart on your computer.

Learn more about how to save seeds, including how-to videos, by visiting our Seed-Saving 101 Guide.