Community Life Among Plants
IF YOU have ever visited Germany, you may have noticed, in the suburbs of cities, large plots of land subdivided into many small gardens. The entire plot of land may have from fifty to two hundred gardens. Much of this land is owned by associations, and only those belonging to an association may rent a garden. Others are privately owned. Much can be learned about gardening here, so we want to take you along as we visit Hans. He is a member of the board of directors of the local “Kleingarten” (small garden) association and serves as adviser for the individual gardeners.
Lately the gardeners experienced some trouble. It seems that they had heard a talk on “mixed culture.” Full of enthusiasm, they went to the garden to try out the suggestions. And the result? Well, it was a little disappointing to say the least.
“Hello, Hans!” He was suddenly interrupted in his thoughts. “Good morning, Werner!” he answered. “How is it you are out so early this morning?”
“Oh, you know how I enjoy working in the garden. But you’re not getting away from me today. I’ve several questions for you to answer. You know about my fiasco with this ‘mixed culture’ gardening. What I’d like to know is just what went wrong and what I failed to consider.”
“Ja, Werner, that is not so easily explained. This is because there are many things that have to be considered. Let’s start with the nature of the soil and the influence that plants have upon one another.
What Part Does Soil Quality Play?
“Did you know that you aren’t the only one working in your garden? Caterpillars, earthworms, yes, and an army of microorganisms in the form of algae, bacteria and fungi are very helpful to you. All of your efforts would often be useless if these microorganisms weren’t busy. What good would it do if you wore yourself out trying to keep the soil loose, and then along came the next rainstorm and the tiny granules would all fall back together so that the ground was once again hard and impenetrable?”
“But what part do these organisms play in keeping the soil loose, and how did they get there in the first place?”
“Don’t you always try to enrich the soil by mixing mature compost into it? A luxuriant fungus growth results, consisting of an extensive network of fungus threads. These small threads with a very short life-span secure the tiny particles of soil so that they cannot fall back together. Later bacteria take over the work, but they are not the last of their kind to work on the soil.
“There is an unbroken chain of life in many forms prevailing in the soil. These see to it that the soil is kept in good tilth, which means that the particles of earth are preserved so that warmth and water can get into the ground. At the same time these microorganisms decompose the material in the ground so that the nutritive value that is in the soil can be released and made available for the plants.”
“But what does all that have to do with ‘mixed plant culture’?”
“Your question is a good one, and I hope I can give you a satisfying answer. Perhaps you remember that during the talk it was shown that much research was carried out. Time and again the natural community life of plants was compared with growing one type of plant. Professor Sekera made an interesting discovery. He found out that there was a much smaller population of various microorganisms in the cultivated field. A mixed plant community, on the other hand, lives with a high microorganic population in the soil.
“Take a look at the natural forests—oak, beech, shrubs and that trailing myrtle or periwinkle that even grows over the luxuriant moss carpet. Every nook and cranny is utilized, and yet not one hinders the others. To the contrary! Each helps the other. And consider that each tree, yes, each plant has its own escort of microorganisms. The result of this is that the soil never gets to the point where it could become ‘tired’ or unproductive. It remains in good tilth and healthy.
“The leafy ‘ceiling’ and the falling leaves serve as a helper for the soil. They protect it from the sun’s scorching rays; they keep it from drying out in the wind and getting muddy in downpours. This too is a provision of the forest for keeping the soil in good tilth.
“Now, you can further such a condition in a miniature way in your garden. For example, let’s say you planted a bed of European broad beans. Soon you would see the individual plants standing rather lonely side by side. The reason is that they cannot tolerate hot weather and have very few branches. There would be no protective leaf foliage to prevent the scorching sun from drying out the soil. Gradually the soil would form a hard crust. The last drops of moisture would escape from the soil through the cracks. Carbonic acid, which the soil has to release for the leaves, would build up in the ground due to the hard crust. And soon the remaining microorganisms, which had not taken refuge in deeper layers of earth because of the lack of moisture, would be poisoned by the carbonic acid. Yes, even the roots would be doomed to suffocate.
“However, if you plant spinach between the rows you would get altogether different results. Spinach grows fast and protects the soil with its wide leaves. Under this protective ceiling the soil stays moist. The result will be just the opposite of the former example. And why? Because of mixed plant culture.”
“That makes sense. But you see what little I’ve accomplished with my mixed plant culture.”
The Influence of One Plant upon Another
“Ja, Werner, you’ve forgotten that plants are also living things. Plants, the same as humans and animals, produce secretions in the process of metabolism, and these can influence other plants beneficially or adversely.
“In this matter Dr. Madaus-Dresen speaks of three different kinds of secretions: smell, root and leaf. Smell and root secretions are in the form of gases. Leaf secretions are of organic and inorganic material found especially on the wet leaves after dew, rain or fog. These materials go back into the soil to fulfill their purpose once again.
“Did you ever smell skunk cabbage? Some plants cannot stand others because of the smell they give off. No one could blame the fennel plant for not wanting wormwood as a close neighbor. This can be easily understood when we consider the results of experiments made by Professor D. Koegel. He found that the smell secretion of wormwood is so strong that fennel 70 centimeters away grew only to a height of 5.7 centimeters. But at a distance of 1.30 meters, the fennel reached its normal height of 39 centimeters. Here the smell secretion had a retarding effect on the growth of the partner plant. Taking this into consideration would be wise when planting your garden.
“With root secretions other interesting things were discovered. It was noticed that the root secretion from one plant had bad effects on plants of the same kind that were in its neighborhood. It seems as though plant secretions from the same kind of plant are not compatible for the neighbor plant. In mixed plant culture, however, the exact opposite was true.”
“Say, Hans, that reminds me of an example in the animal kingdom. A farmer took his cattle to the same pasture year after year. With time, due to the dung of the cattle, there were some especially green spots. The animals refused to eat this grass. One day he came upon the idea of pasturing his horse and sheep in this meadow, and, lo and behold! they ate with gusto the grass that the cattle had refused to eat.”
“When I take a look at your bush beans, I have the feeling that they are just about as unhappy as the cattle that were always pastured on the same meadow.
“Try the same thing the farmer did. Give your bush beans a partner that will ‘eat’ up their metabolic secretions so they can develop in peace. For them the most welcome counterpart is savoy. It takes in their secretions and makes them innocuous, whereas the secretions from savoy are nutritious for the beans. Also in taking nutriments from the soil the two complement each other nicely.
“Do you remember the young apple tree that withered a short time after you had planted it?”
“Ja, that’s right! But I can’t understand how that was possible. Take a look at that young cherry tree; it’s standing in exactly the same spot and is growing like a weed!”
“Think about it for just a bit, Werner. You planted that young apple tree on the very same spot where the old apple tree that was blown down in the storm had stood. In this case it wasn’t only the secretion from the roots but also the remains of the leaf secretions that worked poisonously on the young tree. For the young cherry tree, though, it’s welcome nutrition.”
“Then how was it possible that the old apple tree grew so well?”
“What the young tree wasn’t able to do, the old one succeeded in doing. The old one sent its fine root hairs out far enough so as to be out of the range of its secretions. It found nutrition in the neighborhood of compatible kinds of plants, and in this way built a life companionship that kept it healthy. Naturally you couldn’t see that.”
“How’s that possible?”
“We really know very little about all this. Humble scientists admit that man has a long way to go before he has discovered all the relationships within the plant’s community life. The things already learned, however, are so informative and useful that it pays to discuss and apply them.
How Does Community Life Affect Insects?
“I was thinking here of a special effect that one can produce by gardening with mixed plant culture. How do you explain the recent discovery that insect pests can’t spread as easily in mixed timber?”
“Does that have anything to do with mixed plant culture?”
“By all means! It has been found that the smell secretions of one plant are a good defense against insects for its neighbor plant. A very good example—confirmed by many biologists and horticulturists—is the companionship between the short-leafed early carrot and leeks.
“The enemy of the carrot is the carrot fly, whereas the leek suffers from the onion fly and leek moth. If they live together in companionship, then the strong and strangely different smell of the partner plant repels the insects so much that they do not even attempt to lay their eggs on the neighbor plant. They take off as fast as they can to get away from the smell.
“It’s similar with kohlrabi and radishes in their community life with lettuce. Kohlrabi and radishes are greatly afflicted by earth flies, but when the flies get the smell of lettuce in their nose they take to flight. When plants are affected by diseases, one can usually alleviate the situation by mixed plant culture.
Community Life in Fruit Plantations
“Now that I’ve given you a few tips for your vegetable garden, I‘d like to tell you a little about an entirely different type of community life. You know how much enjoyment I have with my fruit trees. A few ‘Williams Christ’ (Bartlett) pear trees were my pride and joy. But despite the fact that they bloomed year after year, they bore no fruit. It wasn’t due to any lack of bees. One neighbor of mine who had planted the same kind began to take them all out. I waited awhile longer and tried to find the cause.
“Just by chance I happened to get ahold of a pollinization table. Pollen, you know, is the dust from blossoms that is needed to make the plant fruitful. I made an interesting discovery. Pears are noted for self-sterility; that is, the pollen of certain varieties will not pollinate the same variety and so are dependent on the pollen from a different variety of the same kind of fruit. My ‘Williams Christ’ (Bartlett) needed pollen from the ‘Gellerts Butter pear.’ Since neither I nor my neighbor had any of these trees in our garden, the ‘Williams Christ’ couldn’t be pollinated.
“For that reason I got a shoot from the ‘Gellerts Butter pear’ and grafted it into the crown of the ‘Williams Christ.’ The following year this shoot bloomed with the others. The bees took over their share of the work; pears are one kind of fruit that can be pollinated only by insects. What a surprise! A short time later the trees were hanging full of pears. I had grown a little wiser.”
“I’ve found out time and again that there is much to learn!”
“Ja, Werner, it’s just the same as with the universe. The deeper we penetrate, the greater and more unfathomable it becomes. Everything testifies to the unchangeable power of the great, all-wise Creator, to whose laws we have to submit, because they are everywhere, even in the community life of plants.”
[Picture on page 17]
BUSH BEAN
SAVOY CABBAGE
WORMWOOD
FENNEL