How to Avoid Cross Pollination in Your Heirloom Garden

Written by: Luke Marion

Published on April 30, 2021

Updated on October 29, 2026

One of the most rewarding aspects of growing heirloom vegetables is saving the seeds from your favorite varieties to plant again. But if you want those seeds to grow true to type, learning how to avoid cross pollination in your heirloom garden is a must!

Whether you are growing tomatoes, squash, apples, or something else, you’ve probably heard about cross pollination. It can be entertaining when it happens by accident, or frustrating when you end up growing something very different from what you expected!

In this blog post, I will explain what cross pollination is and when it will make a difference, how you can avoid it, and even how to hand pollinate flowers if they need it. Let’s get started!

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A Growing Tradition

Gardening and seed saving used to be essential skills that allowed families and farmers to continue producing food year after year. Today, those wonderful traditions are growing in popularity again!

Here are some free resources to help you get started:

The Importance of Pollination

For those who are wondering what all the fuss is about and why pollination is important, let’s start at the beginning. Pollination is the act of transferring pollen grains from one plant’s anther (the male part of a flower) to a plant’s stigma (the female part of a flower).

While that may seem pretty trivial at first glance, it’s actually life changing! Without pollination, we would lose many of the plants that produce oxygen and provide food. According to the US Department of Agriculture, “[Pollination] is an essential ecological survival function. Without pollinators, the human race and all of Earth's terrestrial ecosystems would not survive.”

What is Cross Pollination

Cross pollination generally occurs when pollen grains are taken from the flower on one plant to the flower of another within the same species or closely related species. That means pollen from eggplants cannot pollinate a melon plant, but pumpkins can cross pollinate with nearby pumpkins and zucchinis.

Successful cross pollination of differing varieties creates a new variety, or hybrid, which is explained more in-depth in Types of Seeds: GMO, Hybrid, & Heirloom. Even though you may hear it talked about in a negative way, cross pollination is not a bad thing, but a natural process.

Sometimes, cross pollination yields amazing new varieties! Watch the video on Butterneck Squash at the beginning of this blog post to learn how new varieties become heirlooms!

The issue is that most growers want consistent, reliable results. When they put a seed in the ground, they want to be confident in what it will produce. (That’s why heirloom vegetable seeds are the most prized.)

If you plant seeds that were cross pollinated, you will end up with unreliable results. To continue the example above, cross pollination between pumpkins and zucchinis creates pump-chini seeds. This is very disappointing if you were trying to grow delicious zucchini for your summer cooking because pump-chinis do not taste good. They don’t even make good Jack O' Lanterns.

When to Avoid Cross Pollination

It’s a good idea to do your research before planting if you want to save seeds. Knowing which varieties have the potential of cross pollination and which varieties don’t can save you a lot of unnecessary work!

Here’s something that surprises most people, even some gardeners: cross pollination doesn’t change the fruit that grows in that season. It changes the genetics of the seeds inside the fruit, which will change the fruit that grows on subsequent generations when those seeds are planted!

That means if you are growing vegetables only to eat and don’t plan to save seeds, you don’t need to worry about cross pollination because it won’t affect your harvest this season. However, if you want to ensure that you will grow the same treasured variety year after year from seeds you have saved, preventing cross pollination is essential.

Nothing beats the beauty of an heirloom with perfect DNA passed on from generation to generation!

Best Methods to Prevent Cross Pollination

There are a handful of ways to avoid cross pollination in your garden:

Isolation by Distance - You can avoid cross pollination by growing different varieties far enough apart that it is unlikely that pollinator activity will carry pollen between them. The distance needed varies by crop. For example, you need to space different tomato plant varieties anywhere from 100 to 150 feet apart at a minimum; some people recommend even further than that!
Isolation by Barriers - Different varieties can also be isolated by using physical barriers like screened enclosures or greenhouses. We demonstrated this in How to Save Bean Seeds when we grew 1500 Year-Old Cave Beans isolated in a greenhouse away from other bean varieties to make sure that they were completely safe from cross pollination.
Isolation by Time - You can also try planting different varieties at different times so that they are not flowering simultaneously, but it can be difficult to reliably predict and control flowering times.
Blossom Bags - I love using blossom bags to eliminate the potential of cross pollination! They are an easy, affordable, and reliable way to protect individual flower clusters without needing a large growing area.

Pro-Tip: There is no need to blossom bag every fruit in your garden! A few blossoms covered will be the perfect amount for seed saving for the following growing season. For instance, if you are growing multiple pepper plants, bag one or more blossoms on each plant for the seeds that you will save. The rest of the flowers can be pollinated by wind and pollinators, and still give you wonderful fruit to eat.

How to Hand Pollinate Plants

To hand pollinate perfect flowers, like tomatoes, peppers, eggplants, and peas, all you need to do is wait until the flowers have bloomed and tap the top of each flower for about 5 to 7 seconds. This can be done while they are inside a blossom bag.

Pumpkins, squash, melons, and cucumbers are different because they produce separate male and female flowers. To produce fruit, pollen must be transferred from a male flower to a female flower.

To hand pollinate these flowers, take the male flower and touch it to the female flower, pulling back the petals and brushing the anther containing the pollen on the stigma inside the female flower petals. You can use a male flower for up to 2-3 female flowers.

Or you can use a clean paintbrush to collect pollen from the male flower and transfer it to the female flower for full pollination. Make sure to be thorough.

Male flowers do not have baby fruit behind the flowers; you will just see a stem. Female flowers have a baby fruit attached to the flower that will eventually grow into a beautiful harvest, especially with these attentive pollinating techniques. (Need more help? Watch this video about identifying the difference between male and female flowers on zucchini.)

What is cross pollination versus self pollination?

Self pollination occurs when pollen from the anther of a flower transfers to the stigma of the same flower or another flower on the same plant, causing fertilization. Cross pollination occurs when pollen grains are taken from the flower of one plant to the flower of a different plant within the same species or closely related species.

Can you save seeds from cross pollinated vegetables?

Yes! You can save and grow seeds even when they were cross pollinated, but the resulting plants may have different characteristics than the parent plant.