A lot of people want to grow heirloom vegetables. The term is most associated with tomatoes. Heirloom however is a created term used for seed classification and it covers all vegetables. I can tell you first what heirlooms are not. They are not first generation hybrids. But if that hybrid has been around for 50 years reseeding itself, it might be classified as an heirloom. Heirloom has more to do with time then anything else.
An heirloom seed must produce the exact vegetable and plant from which it was collected. Time is what is on the side of an heirloom vegetable. Basically, if you plant heirloom seed A you will get 100% of seed A in the plant and vegetable that grows. You always know you get exactly what you plant. Heirloom seeds are open pollinated not hand pollinated like hybrid vegetable seeds. The phrase that is used is 'true to type'. That means the seeds will always produce the exact plant and vegetable no matter how many years you collect that seed.
Time is the question that is not exact for heirloom seeds. The thought is that hybrid tomatoes came into play around 1951. Some people say a tomato seed may be an heirloom if it is pre-1951. Some say it has to be 100 years old. The Brandywine tomatoes date back to 1880. To me, heirloom seeds are seeds that are a part of history and are always true to form when planted. The truth is that people have been cross pollinating all kind of vegetables for 100's of years. Nature has done it for... well since the dawn of time.
A hybrid for a vegetable is two distinct plants cross pollinated to produce a plant with new characteristics or hybrid characteristics. This can be done with purpose and through nature. Corn, peas and squash are three vegetable plants that are easily cross pollinated and open pollinated. That just means that wind and insects can cross pollinate two distinct plants out in the open. If you plant 6 rows of corn with each row of a different corn seed type, the corn seeds you collect will most likely not be 'true to form'. You will have hybrid corn and the seed collected will produce corn that is different the following year. You may or may not be able to tell the difference. That is way they say to plant seed plants with a large space between varieties, if you want to collect 'true seed' to plant the following year.
Hybrids are most commonly seen in your 'tomato hybrids'. They are not heirlooms. They are designed to be small, big, disease resistant, crack resistant and 100 other things. One tomato plant is pollinated by hand with pollen from another tomato plant. The seeds that are produced from that hand pollinated plant are only true one time. The seeds of the seeds will NOT be 'true to type'. Confusing? The new characteristics can only be maintained by cross pollinating. They can not be maintain be seed collecting year after year - technically.
Quality is often associated with heirloom seeds. I think they taste and look better. They haven't been bred into oblivion. In the tomatoes case, hybrids are often designed to be sturdier and in doing so they often give up taste. Tomatoes for stores might be bred to be round, firm and to sit in a boxcar for weeks without rotting. Heirloom tomatoes are often more fragile and taste great at picking. They can't last in a truck for 7 days.
So what is an heirloom tomato seed? It is a seed that has been around for 100 years or more and it is part of our history. The seeds of seeds of seeds with always produce the exact same seed, the exact same plant and the exact same vegetable. They are more colorful, taste better, look round or wrinkled and most of all they aren't cross pollinated hybrids in any way shape or form. They come from all over the world and have been producing the same exact tomato since anyone can remember or read in documents. The same would go for all heirlooms seeds but...
The 'but' is interesting in my opinion. If you cross-pollinated peas (think Mendel) 50, 75 or 100 years ago and those plants produced seed that got planted you would get new seed. With time, eventually planting seeds of seeds of seeds over 50 - 100 years will get you seed that is 'true to type'. Time eventually removes the variance of the original hybrid. It may or may not be a great tasting vegetable but it is 'true to type'. So time will create characteristic stability but for the rare event of mutation. Perhaps this seed becomes a future heirloom.
In the end the word heirloom is a word that was created to mean old and 'true to type'. The time frame may vary from 50 to 75 to 100 to 150 years. Heirlooms taste great because no gardener would save seeds of vegetables that belongs in the compost heap. We are smart, wise and grow what both tastes great and is good for us. Heirlooms have that history bred in them and that is what I like about them.
Enjoy!
