Oak trees are known for their large stature and longevity. Amazingly, a giant oak can grow from just one small acorn. These iconic trees are found in temperate climates around the world.
They are considered to be a keystone species in hardwood forests and provide shelter and food to many mammals, birds, and insects. This hardwood is also used in furniture production, as well as in the production of wine barrels and casks used for aging alcohol. The resulting flavor and color is considered unique.
Oaks are a popular choice for urban landscapes because they provide protective shading, which lowers energy costs for cooling houses in the summer. Like most trees, they store carbon dioxide and expel oxygen, improving air quality. In addition, they drop acorns every fall, allowing you to plant even more oak trees!
For all these reasons and more, you might find yourself wanting to grow an oak tree from local acorns.
The Short Answer
Yes! You can grow an oak tree from an acorn. An acorn is the seed of the oak tree, which means you can plant one and grow a full-sized oak. Oak trees are slow- growing, but once established, they live for hundreds of years. They usually begin producing acorns at around 20 years old. They reach peak acorn production between 50-80 years old. After 80 years, the acorn production begins to slow. Provided that your oak tree is old enough to produce acorns, you can plant them and grow many new trees.
The Long Answer
Yes, you can grow an oak tree from an acorn, however… there can be some complications along the way. Acorns can become afflicted by weevil infestations. You’ll also have to compete with the local fauna that uses the nuts as a food source. This includes blue jays and squirrels that love to cache acorns for the winter.
In addition, acorns are only able to germinate once they are fully ripe. Below we’ll discuss these potential challenges, along with how to identify and rectify them so you can turn your acorns into oak trees.
Do Acorn Weevils Affect Germination Rates?
Acorns can become infested by weevils, causing damage and sterilization.
Oak acorns are particularly prone to becoming infested with weevils. Specifically, Curculio glandium, which is commonly referred to as the acorn or nut weevil. Adult weevils chew through immature nuts and lay eggs inside. As the nut matures, it heals over, and the larvae are protected within.
Generally, you will still be able to see a tiny pinhole, which indicates the weevil is present. In areas where infestations are high, they affect 70-90% of acorns on a single tree. Once the acorn is infested with a weevil, it will no longer germinate.
There are some recommendations for heat-treating acorns to kill the weevil inside while maintaining acorn viability. This method involves heating water to a temperature no higher than 120 degrees Fahrenheit (49 degrees Celsius) and leaving the acorn to soak to kill the weevil. Temperatures any higher than this render the acorn sterile. This is fine if you want to eat the acorns (more on that later), but not preferred if you want to plant them. It’s also impossible to see inside the acorn to assess the amount of damage that the larvae have already done.
Therefore, if you come across an acorn with visible weevil damage, it’s best to move on. Unfortunately, you cannot grow an oak tree from a weevil-infested acorn.
Testing for Weevils
Perform a float test by placing acorns in water; floating indicates weevil damage.
In addition to spotting the tiny pinhole on the outside of the acorn, perform a float test to determine if the acorn has been infested with a weevil. Place your acorns in a bucket or bowl of water. An acorn that floats to the top has a weevil inside. This is due to insect damage that causes an air gap between the nut and the outer shell.
An acorn that sinks to the bottom is undamaged and ready for planting. This is a straightforward method for sorting through large amounts of oak nuts to determine which will prove viable for planting.
Weevils are commonly found in acorns, and they prevent the seed from germinating. You cannot grow an oak tree from a weevil-infested acorn. There are some visible signs to look for, including pin holes and acorns that float in a bucket of water. Although heat treating can be successful in some cases, it’s best to discard the ones that are infested with weevils. A weevil-free acorn is your best bet for strong germination rates.
Do Blue Jays Indicate Pest-Free Acorns?
These birds love acorns, but their presence doesn’t guarantee pest-free acorns.
Blue jays love acorns! During the early fall, their instinct to store nuts for the winter kicks into overdrive. This is right around the time that acorns are reaching maturity. In the first year that my oak tree started to produce mature acorns, the blue jays were pulling them off of the tree before I could even get to them!
These corvids are known for their intelligence. In fact, they are so smart that they can tell which acorns are infected with weevils (without a float test!), leading some to believe that the presence of feasting blue jays may indicate weevil-free acorns. So, does the presence of blue jays indicate a pest-free acorn harvest?
Unfortunately, no, the weevils are a tasty protein-packed treat for a blue jay to find inside an acorn, and they don’t mind eating them along with the nut one bit. So, if you see blue jays feasting at an oak tree, this doesn’t necessarily mean that the acorns are pest-free.
Where this blue jay talent comes into play is the storage of these nuts. Blue jays eat the infested nuts immediately and save the unaffected ones for later. An infected acorn would not last very long in a blue jay cache, so they’ve developed the ability to identify and sort them. How cool is that?
Just because blue jays can identify infested acorns does not mean that nuts from a tree frequented by them will be unaffected by weevils. Your best bet is still to perform a visual inspection and/or float test to determine seed viability.
How to Protect Newly Planted Acorns from Squirrels
Shelter oak seeds from squirrels by covering with mesh or a cage until sprouting.
In addition to your acorns being stolen by the birds, small mammals like squirrels also prepare for winter by caching nuts. And squirrels are arguably not as smart as the blue jays! They forget, at a much higher rate than blue jays, where they’ve buried their stored nuts. This leads to squirrels accidentally planting countless trees throughout their lifetime.
This means you’ll have to protect your newly planted acorns from squirrels, who end up digging up everything from nuts to flower bulbs to add to their winter stash. This happens from time to time with my tulips. The squirrels dig them up and relocate them into the stash. It always makes me smile when I see a tulip come up in a place that I didn’t plant it, as I know it was a forgetful squirrel at work.
For this reason, whether you plant your acorn directly in the ground or a container, cover it with wire mesh or a critter cage to prevent your acorns from being dug up. Once the acorns have sprouted, the squirrel will have no interest, and you can remove any protection.
Squirrels also love acorns and cache them alongside other nuts for the winter when food is scarce. When planting acorns to grow into oak trees, provide them with protection until they sprout to prevent them from being dug up.
Do Acorns Require Cold Stratification to Germinate?
Oak nuts germinate in autumn without cold stratification, needing only consistent moisture to survive winter.
The short answer is no, they do not! Most nuts/seeds that fall to the ground in the autumn will lie dormant over winter and sprout in the spring. That’s because they need to experience the period of cool and moist weather provided by the winter, known as cold stratification, to germinate.
Acorns, however, don’t need this period of cool weather. All they need is consistent moisture. They germinate in the autumn and survive over winter as young trees.
Acorns do not require cold stratification. They can sprout in the same season they have fallen from the tree. The most important thing is to provide them with consistent moisture until they germinate.
How Do You Tell When An Acorn is Ripe?
Ripe acorns are fully brown with no green, falling from the tree when mature.
When acorns first begin to form, they are small and completely green. As they mature, they slowly turn brown. When they are fully mature, they are completely brown with no green color remaining.
Generally, acorns fall from the tree once they are ripe, but they can also be knocked from the tree before then. When they are attached to the tree, they have what is commonly referred to as a “hat.” This cap is called a cupule. The hat will fall off once the acorn is ripe. If an acorn has fallen from the tree and still has the hat attached, then it is likely not mature.
It’s important to be able to identify when acorns are ripe because an unripe acorn will not germinate. It’s also important to only harvest ripe acorns if you want to eat them. You should never eat under-ripe acorns. Under-ripe acorns contain high levels of tannins that can cause gastrointestinal distress.
Ripe acorns also contain tannins, but less so than their under-ripe counterparts. And the tannins can be leached from the nut, thus making it safe to eat. After shelling the nuts, soak them in water for at least 12 hours. Then, drain the water and repeat until it’s clear. It will be dark brown at first and turn lighter in color as the tannins leach out. The acorns can then be roasted and eaten whole or ground into flour and used in baked goods!
Whether you’re planting or eating your acorns, you need to know how to distinguish between under-ripe and ripe nuts. Ripe nuts are dark brown without any green, and they have no cap. If it turns out that you love the taste of acorns, then you have another reason to plant more oak trees!
Oak trees are beautiful and beneficial for your local habitat. They provide food for animals and food for you, too! Once you’ve learned how to identify and sort infected acorns, plant them and grow more trees! The key is to choose acorns that…
- Are smooth without a noticeable pinhole
- Sink to the bottom of a bucket of water during a float test
- No longer have a “hat” (the cap falls off when they ripen)
- Are dark brown without any green
- Safe from birds and squirrels
Consider adding one of these long-lived mighty oaks to your landscaping, and you won’t regret it!