It's planting season, which means farmers across the United States are busy putting seeds in the ground! One of my favorite quotes comes to mind:
"Don't judge each day by the harvest you reap but by the seeds that you plant."
- Robert Louis Stevenson
In Kansas, recommended planting dates for corn range from early April to mid-May.
Southeast Kansas plants first, northwest Kansas plants last – this is partially because of the desert-like climate in the western portion of the state, prolonging lower nighttime temperatures later into the spring. Recommended planting dates are based on such things as the average last spring freeze date and soil temperatures! The map below is taken from the K-State Climatologist website, and the link to more resources like it is at the end of this post.
Actual calendar dates are technically unimportant, but planting too late can cause pollination issues and may increase fall frost damage risk! Soil temperatures must be consistently above 50 °F with good moisture for corn to be successfully planted. For a closer look at the risks of planting early and COOL temperatures at planting, check out my post Cold feet?.
So what exactly is IN these seeds we're putting in the ground?
First of all, that corn "seed" is technically a full-fledged fruit. Every kernel is a single-seeded grass fruit called a caryopsis (pronounced "carry-OP-sis").
Every kernel is covered in a protective layer called the pericarp ("PAIR-uh-carp"), which (in corn and other grasses) is fused with the seed coat. Other "typical fruit" pericarps are the portion we enjoy eating - like the fleshy part of peaches! The aleurone ("AL-yer-own") layer is found directly under the pericarp and is important to the germination process.
Most of a corn "seed" (calling it a seed, but we're understanding it as a whole "fruit" now, right?) is starch, called endosperm. This starch is formed with the "leftovers" of the egg fertilization process following pollination. Each little grain of pollen has two sperm cells, which land on the ear silks and travel down to each kernel. One sperm cell joins with the ovule and other other becomes the endosperm. This starch is really important to seed success, because it provides fuel for seedlings before they are able to photosynthesize on their own!
Corn is a monocot, which means (among other things) that it only has one cotyledon (pronounced "cod-uh-LEAD-un") in its seed. In grass crops, the cotyledon is known as the scutellum ("skoo-TELL-um"), and it serves as an energy source in addition to an enzyme aid for digesting the endosperm starch.
The embryo is the living portion of the seed, and includes the radicle (root), plumule (shoot), and cotyledon. ("RAD-ick-ul" + "PLOO-mule") To protect the delicate embryo, the coleoptile ("co-lee-OP-till") covers the plumule and the coleorhiza ("co-lee-uh-RISE-uh") covers the radicle. In the seed, the living (but dormant) embryo will already have 4-5 pre-developed leaves in its plumule. That’s 25% of the plant’s leaves!
Realistically, corn kernels could be broken and still germinate if only endosperm (which is non-living) was damaged. However, broken seeds are more likely to produce weak seedlings and be impacted by fungus or bacteria.
The pedicel or “tip cap” is the part of the seed that was previously connected to the corn cob. Scratching this structure back reveals a black layer equivalent to the kernel’s “belly button”.
FUN FACT: Corn kernels consistently have an endosperm side & an embryo side. The embryo side is always "adaxial" - farthest from the cob attachment to the stem and facing the tip of the ear!
So what are we REALLY planting when we put those corn seeds in the ground?
Single-seeded fruits called "caryopses" (singular - "caryopsis").
Living but dormant embryos with 25% of their leaves already developed.
Energy needed to kick-start those seedlings.
Chemical reactions waiting to happen - **cue GERMINATION!**
Some food for thought when you're bouncing around in the planter this week!
Stay safe out there and hang around to review what happens during GERMINATION + EMERGENCE!
Climatologist Office. (2021). Kansas climate. Kansas State University. https://climate.k-state.edu/
Nielsen, R. L. (2013). Corn, the great american crop. Corny News Network (Purdue University). www.agry.purdue.edu/ext/corn/news/timeless/Corn.html#:~:text=Three%20important%20parts%20of%20the,attack%20by%20fungi%20and%20bacteria.&text=The%20embryo%20also%20contains%20a,important%20for%20the%20germination%20process.
Nielsen, R.L. (2019). Visual Indicators of Germination in Corn. Corny News Network (Purdue University). https://www.agry.purdue.edu/ext/corn/news/timeless/GerminationEvents.html#:~:text=Germination%20is%20triggered%20by%20absorption,may%20slow%20or%20stop%20germination.