Balancing Crop Profitability and Plant Populations

Today’s post wrap up this series on seed economics (that began here.) The topic of plant population sizes came up during the last ECOSGN meeting as we compared the profitability of selling seeds by packet vs. bulk.

The Challenge: Profit vs. Population Size

Andrea Berry (of Hope seeds) noted that seed companies that mainly distribute small seed packets don’t need to grow many plants to meet their seed needs. Andrea highlighted that to maintain good genetic diversity in cross-pollinating (crosser) varieties, it is better to grow a large number of plants. This means at least 60-80 but preferably around 200 plants (read this post for more on population size). That many plants produces way more seed than most seed companies can sell solely in packets. Andrea concluded that the potential profit of selling seeds in packets is a disincentive to maintaining large plant populations.

Seed growers need to take the possibility of eroding plant genetics seriously. Growing seed out with inadequate populations for 1-2 generations might not have drastic consequences. But, if we grow a crosser variety out for 4-5 generations with small populations, we may see decreases in yields, disease tolerance, and some of the varieties’s desired traits.

Some solutions for small seed companies to maintain good crosser genetics

  • Grow seed in one year for multiple years,
  • Offer bulk seed for sale to gardeners and farmers, or other seed companies,
  • Buy new seed every 2-3 generations to replace or reinvigorate your stock seed,
  • Buy seed from growers who maintain large populations.

An important exception: Cucurbits

Cucurbit species (squash, zukes, cukes, melons, and the like) are crossers. However, they have evolved to resist most inbreeding depression – you only need to save seed from 12-16 plants to maintain  a minimum genetic breadth for a variety  (though more is always better.)

Wrapping Up Seed Economics 101

This is my last post on seed profitability for now. We’ve looked at two quick tools to compare seed crops: profit in space and profit in time. Of course seed crops are only profitable if you can sell them. (This is speaking economically. There are a slew of ecological and agricultural reasons to grow your own seed.) I will tackle the seed selling part of the equation later this spring – specifically selling bulk seed to seed companies on contract.

Over the next weeks, I will switch to more pictures and less math. At Tourne-Sol farm, we are currently building a catterpillar tunnel. When we’re finished, I will share how we did that. See you later!

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