Plant Growing Orientation – How Do Plants Know Which Way Is Up


When you start seeds or plant bulbs, do you ever wonder how plants know which way to grow? It’s something we take for granted most of the time, but when you think about it, you have to wonder. The seed or bulb is buried in dark soil and, yet, it somehow knows to send roots down and stems up. Science can explain how they do it.

Orientation of Plant Growth

The question of plant growing orientation is one scientists and gardeners have been asking for at least a few hundred years. In the 1800’s, researchers hypothesized that the stems and leaves grew up toward light and the roots down toward water.

To test the idea, they put a light under a plant and covered the top of the soil with water. The plants reoriented and still grew roots down toward the light and stems up toward the water. Once seedlings emerge from the soil, they can grow in the direction of a light source. This is known as phototropism, but it doesn’t explain how the seed or bulb in the soil knows which way to go.

About 200 years ago, Thomas Knight tried to test the idea that gravity played a role. He attached seedlings to a wooden disc and set it rotating rapidly enough to simulate the force of gravity. Sure enough, the roots grew outward, in the direction of simulated gravity, while the stems and leaves pointed to the center of the circle.

How Do Plants Know Which Way is Up?

The orientation of plant growth is related to gravity, but how do they know? We have little stones in the ear cavity that move in response to gravity, which helps us determine up from down, but plants don’t have ears, unless, of course, it’s corn (LOL).

There is no definite answer to explain how plants sense gravity, but there is a likely idea. There are special cells at the tips of roots that contain statoliths. These are small, ball shaped structures. They may act like marbles in a jar that move in response to the orientation of a plant relative to gravitational pull.

As statoliths orient relative to that force, the specialized cells that contain them probably signal other cells. This tells them where up and down are and which way to grow. A study to prove this idea grew plants in space where there is essentially no gravity. The seedlings grew in all directions, proving they could not sense which way was up or down without gravity.

You can even test this out yourself. Next time you’re planting bulbs, for example, and directed to do so pointy side up, place one sideways. You’ll find that the bulbs will sprout anyway, as nature seems to always find a way.


History of Watermelon Plants

Watermelons probably originated almost 5,000 years ago in the Kalahari Desert of Africa where botanists have found its wild ancestors still growing. Watermelons migrated north through Egypt, and during the Roman era they were cultivated and prized. Hieroglyphics on the walls of Egyptian buildings tell stories of their harvest. Watermelons were buried in the tombs of kings to nourish them in the afterlife. Melons spread across the European continent and particularly flourished in the warmer Mediterranean areas. Watermelons were documented in 1629 in Massachusetts. During the Civil War, the Confederate Army boiled watermelon to make molasses for cooking. It is in the Southern states such as the Carolinas and Georgia where watermelons flourish as commercial crops. Numerous varieties were developed, and variations of flesh color surfaced. By the late 1800s, the W. Atlee Burpee & Co. was developing its own watermelon varieties and selling seeds.


Vegetable Garden row/Bed orientation: E-W or N-S?

posted 9 years ago

  • posted 9 years ago

  • Things to consider are the slope aspect, drainage and airflow. If the slope is steep, then try to keep rows relatively perpendicular to the slope. Eliot Coleman wrote in his book "The New Organic Gardener" that folks who in the southern parts of the US shouldn't be as concerned with orientation of garden rows. Further north he recommended orienting them East West to take advantage of the fact that the sun is less direct and there will be less shade effect.

    "You may never know what results come of your action, but if you do nothing there will be no result”
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    posted 9 years ago

  • posted 9 years ago

  • Leila Rich wrote: N-S.
    . to get tall plants where they won't shade out low-growers, they need to go at the S end of a N-S bed.
    BTW, that info is particular to my Southern hemisphere, temperate situation.

    Thanks for the translation. I had to go with E-W orientation due to existing conditions and now I'm thinking that the taller plants (toward the north side of the bed, here in the states) will make it hard to reach in from that side. Also, they are raised HK so I have created small south and north-facing slopes due to the E-W orientation. I'm not too concerned overall, but I agree that E-W is probably better if it works for your air flow and drainage regime.

    I like this sort of thing.

    posted 9 years ago

  • My land is flat. I have no contours to follow. Using E-W, tall plants can be used to produce shade when planted on the south side of a bed. On the North side of a bed the shade lands in the pathways. This only matters in during winter in the morning/evening. The rest of the time the sun is directly overhead.

    In NY I followed the contour. In town down here, I had some E-W, some N-S. Out here in the woods I'm going E-W except near the fence where the fence is N-S. The plants don't seem to mind as long as they get water.

    Seed the Mind, Harvest Ideas.
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    posted 9 years ago

  • Replies so far have noted several factors to consider. As always it begins with your local situation. In my situation--semi-arid, high elevation--I'm not so concerned about maximizing sunlight. Light is intense here and there are few cloudy days. Moisture is at a premium though, so I orient my beds across contours to slow the flow of water down the slope. Elliot Coleman also indicates that a slope of a few degrees to the south will capture more solar rays and raise temp.s a couple of degrees. My observations seem to confirm that and since I'm looking to extend my 100 day growing season significantly, I try to build beds so that the top surface has a southward slope. Fortunately the larger scale slope allows me to orient beds generally E-W to easily allow for a southward sloping bed tops. In my annual market garden I do grow taller stuff on the N half of E-W oriented beds and shorter stuff on the S half. I don't mind the taller stuff shading the paths between my beds at mid-day. In fact I like to take it a step further and mulch my paths with lots of wood chips to maximise the absorption of water and minimize evaporation.

    In my winter beds--under a hoophouse or low tunnel--I grow greens randomly, broadcasting a mix of seed. The plants seem to naturally grow in clumps. The air temperature at ground level within those clumps is higher than in the more barren areas (it's all mulched fairly heavily) in between them. Even in this relatively moderate winter, we've had single digit lows regularly. These greens wouldn't have survived the temperatures without several layers of agribon--enough to reduce the block 50-80% of the sunlight according to the manufacturer's ratings--and one of plastic. Early on I removed the agribon regularly on sunny days in order to maximise the sunlight. More recently I've found that the plants did just as well being covered all the time. I've concluded that their growth is going to be slow regardless and that temperature is more of a limiting factor than sunlight.

    I have some further reservations about orienting plantings/bed in order to maximise sunlight, at least outside of areas where sunlight, rather than moisture or warmth is at a premium. The amount of solar radiation striking the earth over the course of a day follows a bell curve, with the maximum intensity in the middle of the day and the proportion of energy building up and tailing off sharply. If I was more concerned about maximizing sunlight, I'd want to find out more about how much plants depend on the intense mid-day sun versus perhaps how little they can get from the relatively weak morning and evening sun. Perhaps it only makes sense to maximise for mid-day sun as working to get more early and late day sun can't really net you much more solar radiation? Another dimension to my reservations is that forests and grasslands everywhere seem to get enough sunlight without worrying about bed orientation. And for all its faults, conventional ag--both pre and post industrialization--seems to have enough sunlight to grow crops without growing in raised beds oriented in any particular direction.

    I'm in the foothills of the San Pedro Mountains in northern New Mexico--at 7600' with about 15" of precipitation, zone 4b historically--growing vegetables for the local farmer's market, working at season-extension, looking to use more permaculture techniques and join with other people around here to start and grow for farmers markets.


    Watch the video: Why dont plants grow upside down? Washington University


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