Heirloom Seeds, Hybrid Seeds and Cross-Pollination

In this post, let's venture into the world of seeds, seed-saving and have cross-pollination explained.

Seed saving is a wonderful thing. It's cost effective and you can save seed from your strongest plants that grow the best in your own garden, so you know they'll grow well each year.

However, not all seeds should be saved, such as those from hybrids. Some plants can cross with each other and the off spring won't be what you expect.

So what crosses with what? First we need to understand the difference between hybrid and heirloom seeds.

Hybrid Seeds

Hybrid seeds are the seeds produced by plants that have been cross-pollinated. This means the pollen from one variety of plant has been transferred to a different variety of plant in the same species.

Hybrid seeds produced by seed companies are made very deliberately. Plants will be picked based on things like their size, disease resistance, and yield and cross-pollinated to produce an elite sort of plant. When you sow these seeds you will get consistent results, and strong plants.

However, when it comes time to save the next year's seeds, the offspring produced by that plant you grew won't be the same, and is usually of poorer quality than the parent plant. Therefore, you will have to re-buy hybrid seeds each year instead of seed saving.

Seedlings purchased at the garden store are most often hybrid varieties.

Heirloom Seeds (or heritage seeds)

An heirloom is defined as something special, of value, handed down from generation to generation. It's the same with heirloom (or heritage as they're also known) seeds. These seeds are from plants grown by our ancestors and passed down, each baby seedling a pretty much exact replica of the parent plant.

Heirloom seeds are open-pollinated and will produce seeds that are 'true to type'. This means they are either self-pollinated or pollinated by a plant in the same species to then produce offspring that are akin to their parent plant.

However, to keep these heirloom seeds true to type, you must ensure they don't accidentally get pollinated by a different plant in the same species.

A spaghetti squash female flower pollinated by a male zucchini flower will still produce a spaghetti squash. But now, if you were to save the seeds of that spaghetti squash that formed and plant those, you would end up with a zucchini/spaghetti squash hybrid cross.

*Corn is different. When one variety of corn is cross-pollinated with another variety of corn you will see the cross-pollinated results in this year's harvest.

Cross-pollination: What can cross-pollinate with what?

For vegetables that are self-pollinating such as tomatoes, peas and beans, cross-pollination is very rare.

For those that need insect help to pollinate, cross-pollination can be really likely.

Plants are sorted into families and each family has groups called Genera (or genus for a singular group.) These genera are made up of many species.

As a general rule, plants only cross-pollinate with the plants of the same species.

For example the cucurbit family, Cucurbitaceae (which includes cucumbers and pumpkins) is made up of 95 genera. Those genera are made up of over 950 species. As it is such a large group, there is often confusion about what can cross with what.

Here are three main genera of cucurbits: Curcurbita, Cucumis and Citrullus.

• Cucurbita: This genus includes pumpkins, squash, zucchini. Within this genus, there are three main species
  a) Cucurbita maxima: A few examples include: banana squash, buttercup squash, Jarrahdale pumpkin, Turks turban, Queensland blue, crown prince...
  b) Cucurbita moschata:  A few examples include: butternut squash, tromboncino...
  c) Cucurbita pepo:  A few examples include: zucchini, patty pan squash, acorn squash, spaghetti squash, baby bear...
• Cucumis: Cucumbers and some melons (rock melons, kiwano, honeydew)
• Citrullus: Watermelon

As a general but lose rule in the vegetable garden, the buttercup squash (c.maxima) will not cross-pollinate with a butternut squash (c.pepo). 

A zucchini (c.pepo) will cross-pollinate with an acorn squash (c.pepo.)

A cucumber will definitely not cross with a Jarrahdale pumpkin as they aren't just a different species, they're a different genus entirely.

However scientific work on interspecific hybridisation is being done all the time so it's hard to have a solid rule in place. The honey-nut squash for example was a specially developed cross-bred cultivar of the buttercup squash (c.maxima) and the butternut squash (c.pepo). It was created by professor Richard W. Robinson at Cornell University in the 1980s.

Brassicas

Another large family of vegetables is the brassica family in which there are thousands of species. The most common species we know in the vegetable garden is B. oleracea, which includes broccoli, cauliflower, kale, khol rabi to name a few. Brassicas are not self pollinating so if they go to seed they will cross pollinate with plants in the same species.

So what's better, hybrid or heirloom?

Hybrids are faster, stronger and usually produce better than heirloom plants. They are however a one trick pony. You will need to rebuy them every year which puts you out of pocket and fills the pockets of the giant seed companies. Though hybrid seeds produce plants that are disease resistant and can mass produce, this is often at the expense of taste and nutrients. An heirloom tomato will often have more flavour and vitamins than a hybrid.

The act of seed saving that heirloom produce allows is more than just saving money. It's amazing to know you are growing the exact same plant that grew hundreds of years ago. Koanga Institue in New Zealand does some amazing work with keeping NZ heirloom varieties alive. Their selection is just awesome, so many delicious varieties. Buy one packet of seeds and you can grow and save seed forever!

Ultimately the choice is yours but if you haven't tried seed saving yet, I encourage you to give it a go! It's extremely satisfying to be able to continue planting each year without the need to purchase more seed.

Happy gardening!

Read more gardening tips on companion planting, crop rotation and no-dig gardening.