What it takes to be a giant

On a walk around the San Jose neighborhood, I encountered a single absolutely giant sunflower in a sidewalk garden.

giant sunflower

I admired the size of the flower head, which was about 16 inches across and probably weighed 10 pounds, wondering how many seeds must be packed in so very tightly and mathematically precisely (see an earlier post on “how many seeds in a sunflower seed head?”).

giant sunflower

Seeds are precisely arranged in spiral rows to maximize packing.

But then I got to thinking about what it takes to produce that giant flower head and develop all those seeds.  Supported by enhanced woody fibers in the stalk and fed by photosynthetic machinery in huge, oversized leaves and an elongated, deep taproot reaching deep into the soil for water and nutrients, the enormous reproductive output of this plant has the potential to be record-breaking.

But alas, a quick google search confirmed that Hans-Peter Schaffer holds the Guinness record for sunflower height (30 feet, 1 inch), mine was probably just over 8 feet. The giant Mongolian sunflowers routinely grow to 16-18 feet and sport 18-24 inch flower disks, so my giant wasn’t really record breaking at all.  Still impressive for an herbaceous plant, though!

How many seeds in a sunflower seed head?

I planted giant sunflowers in the back of the vegetable garden this year, just on a whim to see if I could provide some “natural” food for the birds.  The plants did indeed become gigantic — more than 12 feet tall (see Sept 2 post).   The flowers were about 8 inches across, and attracted a variety of pollinators, but were most attractive to the bumblebees (one is working on the giant sunflower below).

Unfortunately, it wasn’t the birds who discovered the maturing seed heads, it was the squirrels, who were climbing the stalks and pulling the flowers over and eating them.  So, I had to harvest the flower heads a little early, before the seeds in the center had a chance to mature.  Even though slightly immature, these seed heads were enormous (compare with camera lens cover).  You can see the squirrel damage on the flower on the left.

Some of the disk flowers had not dropped off yet, but there were maturing seeds underneath.  These flowers are a testament to the pollination efficiency of those bees, as illustrated below (with disk flowers removed).  If there ever were a demonstration of the eco-service provided by bees, this has to be it.  It looks like almost every single one of those disk flowers got pollinated and fertilized and has at least tried (less successfully in the center) to produce a seed.

You can see the beautiful geometric pattern of spirals that promotes the most efficient seed packing into limited space (read about the “golden angle” in the post on Sept 2).  But just to drive the point home, here’s a close-up.

So you can better appreciate the geometric spiralling pattern, I drew on the seed head to help me keep track while counting seeds.  Yes, counting the seeds, because I wanted to know how many seeds were in a 6.25 inch diameter sunflower seed head.

Now, here’s the interactive part of this post.

How many seeds do you think there were in this seed head?