How do seeds which have a very hard shell, such as walnuts and hazelnuts, get out of that shell (without being eaten) and into the ground? Other types of seeds, such as raspberries, are obviously meant to be eaten before landing on the ground as droppings, since they can pass straight through the digestive system. Squirrels and mice open up hazelnut shells, but presumably the eating and digesting of the nut itself would destroy it and its potential for growth, wouldn’t it? Is the shell meant to rot? In that case how would the rotting process not also affect the nut? Do shells split spontaneously? Have these trees evolved to depend on squirrels forgetting where they have stashed their food supplies?
I know not all “nuts” are nuts, but my question applies to all of the seeds which have very hard shells.
We have hickory trees in our yard, and as the nuts ripen, the soft green husk becomes black and hard and eventually splits exposing the seed/nut inside to germinate. If the squirrels don’t get it first.
Squirrels don’t eat everything they find. They’ll eat enough to fill themselves up and then bury the rest. I remember reading that something like 80% of their hidden seeds are lost.
But I also know that walnut shells degrade fairly quickly. Relatives of mine had a black walnut tree. Opening those nuts by hand was impossible, and you were lucky to make it work with a hammer. But if you found one that been left on the ground over the winter, it had partly decomposed and was much weaker.
It’s also become a recent trend around here (Seattle area) to use hazelnut shells instead of bark for garden landscaping. These shells last a little longer than bark, but you still have to add more every couple of years.
It would be easy to experiment with this yourself - take shells from various nuts, bury them in moist earth for five months and then see what they’re like afterward.
The shells sit through winter and split open for the root to come out and anchor in the ground. The stem is outside the shell and the crown grows from that. The nut meat is attached to the sides of the stem in two places, one for each half. The shell may fall off or not before the food reserve is gone.
So is it actually “rotting”? Because that implies fungus or something similar - in which case how is the seed immune to the rotting? Does there just need to be enough of the unrotted seed exposed for germination to occur? Or if it’s not rotting, is there some clever technique by which the shell is hard when it needs to be and then become soft when the time is right? Or is there a time / temperature / light triggered splitting? In which case why doesn’t that happen with nuts that sit for years in your kitchen? Is moisture the important factor?
The husk covers the shell. The husk is what the shell forms in during the summer.
Examples:
Black Walnut - The husk rots away to expose the shell. The shell splits in half as the root emerges.
Shagbark Hickory, Hican, Pecan, and Chestnut - The husk splits into sections after it starts to dry out and detaches from the shell. The shell splits as the root emerges.
Hazelnut - The shell is covered by two thin leaf like structures that form a very thin husk. The husk dries up and easily breaks up like a fallen leaf in the fall. the shell splits as the root emerges.
Acorn - The shell is attached to a cap which eventually drops off. The root emerges from the pointed end of the shell which breaks open on the bottom.
Many nuts do not have a seam on the shell that opens. The shell just develops cracks at the end the root emerges from.
Most nuts require moisture for a certain time and many require a cycle of winter to pass before they open. Nuts don’t all germinate the next year either as a protection against fire.
I see, thanks for your answers and sorry for misunderstanding your first post.
I have some wild hazelnuts, husks intact, that I found, sitting on my windowsill - they were green when I got them and I thought it would be better to let them dry out before eating them.
What I found with the hazelnuts that seemed to have fallen off the tree first (and so were already brown) was that most of the shells seemed to be pretty much empty when I cracked them (they hadn’t been nabbed by rodents). Would that imply some sort of problem with the tree?
You’ll have to ask someone that has a degree in this field. I can’t tell you details. I did watch a lecturer on what triggers seeds to sprout, and it’s complicated. It’s way beyond my scope to explain. Different environmental conditions trigger chemical reactions in the seeds, some of which stop germination, and others that promote germination.
Untended hazelnuts almost all get eaten out by a filbert worm. Wild ones are not worth the effort to gather and crack. Inside is a nut meat the size of a pea.
The hard seed coat generally splits when it absorbs sufficient moisture. Different seeds require different conditions to germinate. Some need cool/freezing temperatures. Others require heat. Some need to be scraped, and others require sunlight. So some seeds need to overwinter before greminating. Others, such as the dandelion, will greminate any time favorable conditions exist.
As you said, some seeds - even from the same plant - may “skip several seasons.” There are a huge number of ungerminated seeds in every square foot of soil. Many of them simply need the right combination of oxygen, water, heat, and light to germinate. That is one reason why most gardeners advise against unnecessarily cultivating soil - it brings too many unwanted seeds tocloser to the surface where they can/will germinate.
Regarding acorns, some squirrels nibble the end of the acorn to prevent germination.
