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

Wednesday, January 23, 2008

Waiting in the Wings

To harvest, or not to harvest?

There is an art to harvesting mini squash. You have to learn to anticipate how fast the fruit are growing to know when to harvest, and when to leave the fruit to get a little bigger.

There’s always more incipient fruit waiting in the wings. The younger buds and their ovaries (mini squash) grow very slowly while the plant puts most of its resources into growth of the oldest, largest fruit on the vine. Once that largest fruit is picked, or once it has put on most of its growth and starts to mature seeds, the next largest fruit will grow that much faster.

Plant physiologist refer to the fruit as a “sink” for resources such as nutrients transported from the roots, and sugars created by photosynthesis in the leaves. The larger the fruit, the more resources are diverted to that sink. The larger and healthier the plant, the more resources there are to invest in the fruit sinks. When fruits are allowed to grow until the seeds are mature, as in winter squash or melons, then less of the resources go into making stems and leaves. If the fruits are harvested small, and are not allowed to mature, the plant has excess resources for making more flowers and more mini squash, but also more stems and leaves that can, in turn, make even more flowers and mini squash.

I always have this in the back of my mind when I harvest. I have a target size for harvesting the fruit. For zucchini types, mini squash are best at about 4 inches long. Patty pan types are best about 1.5 to 2 inches in diameter. If a fruit is marginal in size when I’m harvesting, I have to decide whether or not to harvest. It’s a game of skill and chance.

I’m looking at the largest fruit, the one that bloomed yesterday or the day before, but also the second largest to see how close it is to harvestable size. Sometimes there are two fruits close together that are almost identical in size. I have to take into account that the plant is probably putting equal resources in each of those fruits, so the two are growing a little slower than one dominant fruit would grow.

If it’s the last squash harvest of the day on Friday, I'll harvest a marginal sized fruit no matter what, because I can bring it to market the next day. Plus, I may not get back to harvest until Sunday morning. On warm days, the squash could be too big by then. Instead, I let the next largest squash become the sink so it will be ready to harvest next time.

If there is time on Fridays I harvest twice; once first thing in the morning, and once at the end of the day. In the morning I’ll leave marginal squash on the vine, in hopes that they will be the perfect size by the end of the day. But if the second largest squash looks like it might be harvestable by the end of the day, I’ll take the largest squash in hopes of harvesting two squash from one plant that day.

Similarly, if it’s a week day, I am inclined to leave a marginal squash on the vine for another day in hopes that it will be perfect the next day. If it’s a warm day, or if I am late harvesting, it may get a little too large. If it’s a cold day, the marginal squash could take several days to reach harvestable size. Then I tend to harvest mini squash at a smaller size.

Sometimes the fruit grows past mini squash size, and I decide to leave it until it’s a “midi” or “maxi” fruit size. Then I aim for a fruit about 7 inches long for zucchini types. That may take several days of growth.

I may notice squash slow pokes. A squash that should be the dominant sink on a plant may not grow as fast as expected. I’ll suspect a stronger sink hidden somewhere at the base of the plant. I often find one – the huge squash that suddenly becomes visible when it reaches baseball bat size.

I have to know my squash plants intimately to play this source-sink harvest game. I remember each fruit configuration from day to day, noting how much has changed since the previous day, watching the sky, the soil, the weather forecast to predict how fast change will occur in the future. Change is constant in my squash patch, and often dramatic, until it is abruptly halted by a heavy frost.

My squash patch is a metaphor for my life. I watch the young seedlings burst forth into the world and grow day by day with the exuberance and uncertainty of children. It takes maturity and experience to recognize and appreciate the rate at which they grow, and to prepare for change. Just when I think I am good at it, the weather changes, the temperature drops. Growth and change occur at a different pace. I have to learn and adapt all over, hoping to continue to be productive until the final frost.

Tuesday, January 8, 2008

First Frost

Ok, so I'm writing this long after the pictures were taken. The last few weeks of fall were hectic. But I have some loose ends to tie up from the squash patch, one of them being the frost.

These photos were taken on Thursday, October 18. When I looked out first thing in the morning the patch looked fine. Midday we had a knock on our door, and there were two women who introduced themselves as Jehovah's Witnesses. I politely indicated that I wasn't really interested in talking with them. They smiled, kindly, and one of the women commented about how nice my garden looked. I thanked her for the compliment. "You haven't been hit by frost yet!" she noted with surprise. Lots of places already had their first frost by then, but I was pleased that frost had thus far missed us.

Perhaps I should have said that I was grateful to God for the garden. Perhaps the damage that I noticed when I went out in the afternoon to harvest was His revenge for my being too smug about my good fortune. But there apparently had been frost damage after all, wilting the outer leaves on my plants, and killing the cucumbers (far left in the top photo) outright. The squash plants were still alive under the dead leaves, but in the cold they were producing very slowly. I spent about 40 minutes that afternoon harvesting 90 small patty pan squash and 40 zucchini squash, a total of about 7.8 lbs. On Friday I did a "salvage" harvest of squashes that are tiny, but still edible. Took another hour, and yielded another 6.9 lbs. Most of it came to the Nampa Farmers' Market with me on Saturday, Oct. 20.

I put the smallest squashes into pint baskets and sold each basket for $1. I sold 9 baskets, plus another $11 worth of larger squash, a total of $19. There was about $9 worth of squash left unsold. No matter, it was just enough for another few meals for us.

There was still a bit of growth left on the plant the following week. On Friday, Oct. 26 I harvested for the last time, about 7.5 lbs. It made up 12 pint baskets of tiny squash, each about 11 oz. (including basket). They sold out. It was our last market of the season.

Soon I hope to post the total yield and income from my 2007 squash patch. This year, 2008, perhaps I'll be able to start earlier and do better. Meanwhile, I've posted the results of my 2006 squash project for SARE on my website. I'll be doing a poster and presentation about it in March at the National SARE conference. Plus, I hope to add some information to this blog about some of the squash research that Ive been reading, and what it tells me about the dynamics of squash growth.