Date Check: Do Seeds Last Forever?

— by Jessica B. Turner, PhD candidate, West Virginia University

It’s a classic blind date story…in the garden. You find a packet of mystery seeds in the back of a drawer, unmarked, no expiration, and you think, I’ll plant these next year, no problem! Come summertime, you’re swooning over fresh juicy tomatoes atop margarita pizza. Way to be immortal, seeds, you think. Even people without a “thing” for planting might assume seeds last forever, thanks to news like this about the crazy-old date seed from 1 CE (AD) that was still viable two thousand-plus years later.

But while it can seem like seeds might grow anytime conditions are favorable (they just need decent dirt, water, and sun, right?)—most don’t stay viable indefinitely, unless they’re stored in super-special conditions.

 Seeds come in all kinds of shapes and sizes — here’s a sampling, courtesy of the Chicago Botanic Garden.
Seeds come in all kinds of shapes and sizes — here’s a sampling, courtesy of the Chicago Botanic Garden.

That’s the short story, according to a bevvy of experts we consulted, from the Chicago Botanic Garden and the Morton Arboretum to Botanic Gardens Conservation International and the USDA-ARS’s National Center for Genetic Resources Preservation.

Now’s the part where you might point out that there are plenty of seeds in the, er, sea, so, why angst about shelf life?

Like Jack’s magic bean seeds, there’s more to each species we can save than meets the eye.

Saving Seeds Saves the Day

Because we’re starting the world’s sixth mass extinction, many plants are under threat of disappearing forever—about 68 percent of evaluated plant species, to be exact. And species loss in turn has a direct impact on day-to-day life (because, coffee).

How does plant diversity affect food supply? For starters, a genetically diverse seed supply helps us avoid potentially losing a bunch of food crops.

Let’s say that a fungus wipes out a main agriculture crop, like it did during the Potato Famine of the 1840s. Because field after field of genetically identical potatoes had been planted, it only took one common potato blight to lead to massive starvation across Ireland.

These are all soybeans! And there’s more species diversity where that came from… (USDA/NCGRP)
These are all soybeans! And there’s more species diversity where that came from… (USDA/NCGRP)

More recently, in the 1970’s, blight wiped out almost 15 percent of corn crops in the U.S., mostly because of the genetic similarity of the corn planted. The simplest way to ensure we don’t lose all our food crops to a common blight? Make like a playlist master and mix it up already.

There’s also a bigger-picture reason to “dig” plant diversity. With diseases like the Dutch Elm Disease, banana-killing fungi, and insect pests like the Emerald Ash Borer threatening plants, along with changing climate issues, if we don’t preserve healthy seeds in the near term, we could be saying goodbye to lots of plants we know and love in the long run. So…let’s make ’em last—by collecting and storing seeds.

Bank This! Or, Seed Storage 101

Enter, seed banks, where countless seed species and varieties are stored in countless glass jars. Seed banks exist around the world as a kind of USB thumb-drive of the mighty plant kingdom, holding a back-up copy of genetic plant material, which can be used for science or in case of emergency.

These banks can generally hold most kinds of seeds, aka orthodox seeds, which can be frozen, dehydrated, and banked for long periods of time. When they’re thawed out down the line, orthodox seeds that have been stored properly can still grow just fine. There are some exceptions, of course. Seeds that can’t be banked are called recalcitrant seeds—we’ll get to those after we first revel in the wonder that is modern seed banking.

Kew’s Millennium Seed Bank boasts a whopping 39,000 species stored in underground vaults. (RBG Kew)
Kew’s Millennium Seed Bank boasts a whopping 39,000 species stored in underground vaults. (RBG Kew)

The big-deal seed bank in Europe is the Millennium Seed Bank Partnership, which is part of the highly esteemed Kew Botanic Gardens in London. Since launching operations at the start of this century, Kew’s Millennium Seed Bank has stored 13 percent of the world’s plant diversity, with close to two billion seeds.

In the U.S., the USDA has its own seed bank, the National Center for Genetic Resources Preservation (NCGRP) in Fort Collins, Colorado, which stores crop plants, wild plants, cultivars, weeds, genetic stocks, and endangered or rare species.

Sometimes seed banks are bomb-proofed and vaulted underground, while others are above-ground buildings. Either way, they’re all kept dry and really, really cold (we’re talking -4 degrees F, so hopefully North Face bodysuits are included in the employee benefits package). They’re not just literally cool, either.

Not Your Ordinary Bankers

While their work may not exactly be a hot topic in water-cooler conversations, seed bankers are supremely cool.

lorenandbillinvaults
At the USDA seed bank in Colorado, “conventional” storage happens in a big freezer at -4F. (NCGRP)

One stunning example of how important they are to the scientific community comes to us from World War II. During the Nazi siege, Russian scientists charged with protecting the resources within the world’s first seed bank, the Pavlovsk Experimental Station, chose to starve to death, rather than eat the roots, grains, and seeds they were protecting.

Dedication to the cause continues. A modern-day seed-banking rockstar, Christina Walters, PhD, of the NCGRP, works to preserve the variations of genes within crops to make sure we have the material in a species to help with drought or disease resistance.

In fact, her team once saved the day for Michigan farmers, when an unseasonably cold winter destroyed the sweet cherry crop. A quick look into the NCGRP seed bank turned up cherry seeds with higher levels of cold tolerance, which enabled farmers to save future crops (and ensure that there’s a cherry festival for Weird Al Yankovic to headline this summer).

So, how do we ensure the proverbial money is in the bank? The first step is to carefully prep the seeds, says Kayri Havens, PhD, pro seed-banker at the Chicago Botanic Garden’s Dixon National Tallgrass Prairie Seed Bank, which has committed to collecting 30 million seeds from 1,500 native species across the Midwest.

Precision is key in preparing prairie seed samples for good banking. (Chicago Botanic Garden)
Precision is key in preparing prairie seed samples for good banking. (Chicago Botanic Garden)

While seeds are indeed “rugged little structures,” Havens says they can still be damaged so it’s important to be precise.

First, researchers collect seeds from the entirety of the species’ range. Then it’s to the x-ray machine they go, to keep bugs from making their way into the collection and to be sure the seed houses an embryo. After seeds have gone into the storage jar, they’ll only come out every 10 years or so, to be retested for germination potential.

“If they are taken care of and processed correctly, seeds can live centuries in suspended animation,” Havens explains. And that’s putting the orthodox seed money in the bank.

Recalci-what? Bank-busting Seeds

Seed banks are awesome—except for when you’re dealing with the aforementioned un-bankable recalcitrant seeds, which includes many tropical seeds. Because they typically don’t need to worry about winter, many of these seeds simply start growing immediately after they’ve fallen to the ground.

Recalcitrant exhibit A: The mighty oak

Wait, head-scratch time: How do oaks fall into this category when they’re so often found buried under two feet of snow? Murphy Westwood, an oak enthusiast at Morton Arboretum and a global tree conservation guru for Botanic Gardens Conservation International explains that even the winterized Midwest oaks evolved from warm areas like Southeast Asia and Mexico.

This little shingle oak could totally turn into a mighty tree! (John Hagstrom/Morton Arboretum)
This little shingle oak could totally turn into a mighty tree! (John Hagstrom/Morton Arboretum)

The fat juicy acorns from the tropical-evolved oak have not evolved to survive the low humidity and low temps of a seed bank. And yet, it’s important to figure out how to preserve our oaks for a bazillion reasons, from providing food and habitat for animals, cleaning ground water, and pulling toxins out of the air…to musical instruments, whiskey, the list goes on.

Lost cause? Nope. Westwood has a few acorn-saving methods up her sleeve.

According to Westwood, you have to pull a Walt Disney (as rumors have it), and preserve the seeds in liquid nitrogen. And, because plants have meristem cells (kinda like human stem cells), it’s also possible to regenerate a plant from a liquid-nitrogen-preserved oak bud, in a process called micro-propagation or tissue culture.

The other option is to create a living collection, essentially a garden of the plants themselves. For example, say you want to preserve a threatened oak species. Your mission would be to determine the distribution of the species, collect acorns, bring them back into a garden and propagate, and finally, collect their produced seeds. Then, these seeds can be sent to other gardens for their collections, or they can be reintroduced back into the wild.

Recalcitrant exhibit B: Avocado dreamin’

Like many tropical plants, avocados are another beloved, yet even trickier, example of a recalcitrant seed.

These grocery store seeds show the diversity of seed storage behavior: Avocados, recalcitrant. Papayas, somewhere in between; cantaloupe, orthodox. (NCGRP)
These grocery store seeds show the diversity of seed storage behavior: Avocados, recalcitrant. Papayas, somewhere in between; cantaloupe, orthodox. (NCGRP)

Not only are their large fleshy pits basically impossible to store, but the way the Hass avocado is grown means there’s little value in storing this species’ seed anyway, according to David Kuhn, PhD.

Why? You might want to sit down for this: They’re. All. Clones. Every Hass avocado in existence came from one tree in one guy’s backyard in California, so no other seed could replicate its fruit.

It’s like this, kids: An avocado seed’s genes are made up from both of the parent plants, so the resulting tree might produce fruit that’s way different from the fruit it came from (smaller, weird tasting, etc.). As you can imagine, farmers aren’t big on this potential for product inconsistency, so they avoid it by doing a kind of branch transplant, where they graft the fruiting branch to the rootstock of another tree.

Instead of trying to save the inimitable seeds of Hass avocados, researchers focus on saving these trees in living collections. The USDA has three major living collections of a whole variety of avocado species, located in Miami, Hawai’i, and Puerto Rico. They’ve got way more than Hass, too: the Miami facility alone boasts roughly 300 additional types of avocado tree species! Here, scientists do genetic research on the plants to learn about and protect avocados from the increasing number of threats to this guacamole staple, such as the fungal disease, laurel wilt.

Seeds, Saved! Now What?

Seed banks and living collections are awesome! But, that doesn’t make them the be-all, end-all solution to our plant diversity challenge.

Every species’ seeds matter! These milkweed seeds, for example, are critical to monarch butterfly survival. (Chicago Botanic Garden)
Ripple effect, in effect: Banking milkweed seeds, and ensuring they’re available to plant when needed, supports monarch populations across North America. (Chicago Botanic Garden)

Storing seed species is an important way to help build up threatened species, explains Walters, but it’s also just one part of a larger species conservation strategy, which should also include a savvy re-introduction plan.

How to create those major long-term strategies? Westwood encourages communication between gardens, governments, and universities to make sure we know which species are where, and what genes are out there.

In terms of planting fresh seeds we all know and love, right here, right now? Seeds the day.

EcoMyth Outcome: Myth Busted

While some seeds seem to be borderline immortal, most seeds don’t last forever—unless they’re carefully stored in seed banks or as living collections. Sometimes, nature has a shelf life. Next time you’re cutting up an avocado for guacamole, think about the world without your sports-watching staple snack, and appreciate the work science is doing to make sure that world doesn’t exist.

One Green Thing

Plant a native tree seedling in your backyard. You’ll be supporting plant diversity with your mini living collection, while scoring the host of other benefits of planting trees.

Myth BUSTED: Treehugging isn't cool
Myth BUSTED: Treehugging isn’t cool

Multiplier Effect: If 1,000 people planted a native tree in their backyard, we could collectively reduce stormwater runoff by 1,685,000 gallons and remove 2,000 pounds of pollutants from the air, according to stats from the City of Minneapolis Municipal Tree Resource.

More ways to help:

  • Plant seeds in optimal growing conditions: Every seed counts, so give the ones in your garden the best shot at life. This includes opting for native plants, which are uniquely suited to your region’s climate.

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