Saturday, February 2, 2008

Bush and Vine Squash

The garden is covered with snow, but with a pile of seed catalogs in hand, I'm starting to think about next season's garden. I pretty much used up all of my squash seeds last year, so this year I need to buy more, including most of the varieties that I grew last year (see my post from September 18, 2007). There were two varieties that I didn't plant last year because I was out of seed. Flying saucer is one of my favorites. It's a patty pan type that is green in the center and pale yellow on the pointed tips. It looks like something from outer space, and the name appeals to kids. I also like geode, a round zucchini, lighter green than eight-ball and a nice match to it. Geode seems moister and more flavorful than eight-ball to me. I'm watching for other varieties that would be good in my mix of baby squash.

Seed catalogs often note that some varieties are bush types, and others are vining. I took some photos last season to illustrate this.

This is zephyr, from Johnny's Seeds. It looks a little like a yellow crookneck squash, except it has smooth skin and the blossom end is green. It's a good example of a vining type. The base of the plant, where the roots go into the ground, is at the left. The growing tip of the vine is on the right where you can see an open flower and tomorrow's flower bud, both with developing ovaries. These ovaries are a little thin for mini squash. I would probably wait a day or two before harvesting them.

Behind the pistilate (female) flowers with their developing ovaries are a series of nodes, each with a stem (pedicel) leading to a broad umbrella-like leaf. Those are the photosynthesis factories that make carbohydrates to fuel further growth of the plant and fruits. One of the nodes In the middle of the stem has branched off to produce more leaves and pistillate flowers. Toward the base of the stem are several wilting flowers, and some buds, all staminate (male) flowers. The plant produces male flowers on older parts of the stem, and female flowers on new growth.

If I were leaving fruits to develop seeds, I would want the bees to visit the staminate flowers and get themselves drenched in pollen, then move over to the pistillate flowers to deposit pollen on the stigma, so the fruit could set seed. Of course, the bee wouldn't care if it was transporting pollen to the stigmas; it would just want to get nectar from the base of the flowers. Both pistillate and staminate flowers produce nectar.

The pistillate flowers produce the squash fruit, but the staminate flowers are another commodity. They can be harvested as squash blossoms, a seasonal favorite at gourmet resaurants, where they make squash blossom soup or wonderful stuffed appetizers. They are a rare commodity because the blossom only lasts one morning. You have to harvest at dawn when the flower is just opening, store them in cold water, and use them by evening. Maybe you can keep them for a day or two in the refrigerator, but that's it.

But back to the vines. As long as I am harvesting baby squash, the photosynthate from those leaves won't be going into any rapidly enlarging fruits. Instead the plant will use the carbohydrates to add another node or a new side branch, produce more pistillate flowers, and more baby squash. It's a nice positive feedback from my perspective. The more I harvest, the more I should have to harvest. My research suggests that I can harvest 1.5 to three times more individual squash if I harvest them small than if I leave them on the vine to grow to a respectable mid-size squash.

If I were growing the squash for seed, I'd wait until the squash grew huge and the seeds matured. While the squash was growing, much of the photosynthate from those leaves would be going to enlarge the fruit. The plant would grow slowly, adding few new nodes. The largest fruit, if well pollinated, would inhibit the growth of smaller fruits developing behind it, possibly even causing them to abort. New flower development also would slow. Plant physiologists call it "first fruit dominance".

I've recently learned that researchers in plant ecology at Penn State University have shown that it's not just a head start in time that gives the first fruit it's dominance. Good pollination is also important. Fruits that are developing many seeds dominate over those that are developing few seeds, even when the fruit with few seeds is older. The researchers have also shown that levels of the plant hormone ethylene are lowest at the tip of the growing plant when there is a dominant fruit developing on the vine. Apparently, ethylene stimulates development of new flowers and fruit; when ethylene is lacking, flowers and fruit are supressed. (Stevenson 1992, Krupnick et al., 1999; see bottom of this entry)

This eight-ball plant is a bush-type squash. They take up less space in the garden, and some bush types are small enough for container growing.
You can see why they are bushy rather than viney: they don't have much stem between the nodes. All of the flowers and fruit are scrunched up in the center of the plant. As they add new leaves, they remind me of multilegged clusters of green octopi.

With the stems so close, it's sometimes hard to see frut developing at the base of the plant, particularly green varieties like eight-ball. I wonder if bees have a hard time getting to flowers at the bottom?

When I pick baby squash, the plant doesn't bother to grow much more stem, just more leaves and flowers on top of each other. These bushy varieties seem to produce flowers and fruit faster than viney varieties, as long as they are well fertilized.

Flying saucer, as I recall is a bushy plant, but very slow growing in comparison to other bushy varieties. I'm not sure why. I'll have to watch it more carefully this season.

Stephenson, A.G. 1992. The regulation of maternal investment in plants. In C. Marshall and J. Grace, eds., "Fruit and Seed Production: Aspects of development, environmental physiology and ecology", Cambridge University Press. pp. 151 - 171.

Krupnick G. A., K. M. Brown, and A. G. Stephenson. 1999. The influence of fruit on the regulation of internal ethylene concentrations and sex expression in Cucurbita texana. Int. J. Plant Sci. 160(2): 321