A Little Bit More
Typical leaves of black oak group
Separating the oaks is not quite as straightforward as the unit poster makes it sound but for many of the oaks, you can break them down into the black or white categories. Of course, nature doesn’t always go by rules that humans make so there are often variations on our own “rules”. Guess that’s what makes things so interesting.
Typical leaves of white oak group
If you’ve looked closely at oak trees and their acorns in the fall, you may have been confused to see that on the black oak group, there were both mature and immature acorns on the tree at the same time. Now you know why – it’s normal. The black oak group that requires 2 years for acorn maturity, includes: the Northern Red Oak, Pin Oak, Black Oak, Shumard Oak, and Southern Red Oak among others. The white oak group includes: Eastern White Oak, Post Oak, Bur Oak, and Chinkapin Oak. Although there are other oaks that don’t fall into the black or white oak categories, these two groupings do help with identification for many oaks across North America. And if you’re interested in acorns for eating, always select those from the white oak group – these have less tannin and are much more palatable.
Activities
Science – Oak Trees Alive
Objectives: See an acorn germinate
Materials: acorns, plastic bag, access to refrigerator
This activity will require a delay between the collection of the acorns and the actual germination but it is one that is well worth waiting for. If you live in warm areas that don’t freeze., your oaks may need little if any dormancy so you can probably shorten, or even eliminate, the length of time for stratification noted below.
Tree field guides have good identification illustrations in their books to help you decide what species you may have. Furthermore, they often include the acorns too as these are often distinctive and help a great deal with oak tree ID. Have fun.
- Ask your students to look for oak trees in their area. Good places to hunt include yards, parks, street trees, or even your own school yard.
- Once you’ve found a tree or two, have them monitor the trees to see if acorns are growing on them (young trees probably won’t have any acorns, you’ll need mature trees). Once they know acorns are available, they’ll need to watch for acorns to begin dropping to the ground. If the trees are on private property, be sure to ask the owners if they can collect a few acorns for a school project – few owners will decline.
- As soon as the acorns drop to the ground, they’re ripe and can be picked up for this activity (you’ll probably have competition with wildlife). These should be placed into a zip lock plastic bag, labeled with the date, and popped into a refrigerator (be sure the acorns aren’t wet when placed in the bag but a wee bit of moisture is fine) HINT – some of the acorns you’ve collected will have insects and/or just not be viable so you can place your acorns in water as a test of quality - those that sink are probably “good” while any that float should be disposed of.
- A chemical process will take place in the refrigerator that’s called stratification. This process changes the acorn’s chemistry and prepares it for germination. In general, the optimum temperature for stratification is 4ºC (39ºF) and takes about 8-10 weeks. Since your refrigerator is probably warmer than this optimum temperature, you’ll need to stratify your seeds a bit longer, say 12-14 weeks to be safe.
- Once the stratification time is completed, you can remove the acorns from the refrigerator and plant them. Plant the seeds in small pots in potting soil, place where the temperature is warm (room temperature is just fine) and moisten. Do not over water but keep the soil moist. If you plant the acorns just below the surface of the soil, you’ll be able to gently brush away the dirt and check out the progress from time to time.
- Acorns are large seeds and therefore require more time to germinate than grass seed, for example. So, be patient. Within a few weeks you should begin to see your acorns split and a seedling emerge. Keep in mind that not ALL of your acorns are likely to germinate even if they passed the “float test”. For various reasons, some will never grow while others seem to do just fine.
Once you have some oak seedlings, you and your class can decide what to do with them. Maybe plant some at the school and monitor their growth over the coming years or simply pass them out to students for planting in their own yards. The larger your oak trees are before planting outside, the better the chances of survival.
Inquiry Activities you may want to pursue
- Can you figure out why the “float test” is an indication of acorns that are not viable? This might make a good question to pursue for students. You may want to weigh acorns that float and those that sink. You may also want to dissect some that float and some that do not and see what you can find out as well.
- Does it make any difference if you plant the acorns with “cap” pointing up or “cap” pointing down? This would make a good mini project to pursue and will require enough in the sample size used (you determine how many you think makes a good sample size) to have any reasonable results.
Key Concepts
Structures and Functions, Reproduction, Life Cycles, Identification, Growth and Development
Questions
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