Supplementary notes to
California Master Gardener Handbook
Chapter 2: Introduction to Horticulture pages 22-26
PLANT GROWTH
Water and light, those are key. In places that are dark and dry not many plants grow. Plants can tolerate the cold as long as there is also a warm period for them to grow and make more babies. If it is cold all the time – no good. Then they hunker down, slow it down, don’t do anything. They are still finding seeds in the arctic and Siberia from 30,000 years ago that when planted today are able to germinate. 30,000 years of Rip Van Winkling!
Plants survive on a variety of soils. From a granite crack in the mountains to the constantly flooding thin soils of the rainforest. From the icy permafrost tundra soils to shifting sand at the beaches. In general, its easier for plants to tunnel through loose soils compared to dense hard soils. That is why you plant your lettuce radishes and tomatoes in friable (easily crumbled) compost rather heavy clay hardpan where it would be strugglin’.
In some cases, the size of the plant above ground is reflective of and similar to its roots under the ground. Imagine the root systems of those oaks on the brown hill ranches all over the state. Four hundred years of massiveness. In other cases a small and nondescript plant above ground may have a huge long root system underground hidden from view. Think about a two hundred year old tiny little alpine plant that lives at 8,000 feet. Its small aboveground because of the wind and weather and snows, but down below it is snuggled and snaking deep into the rocks. You are caressing it saying “Oh you are so cute” and the plant is expressing “I’m old enough to be your grandma five times over”. Depending on its ecology and evolution, plants have a preference for either nutrient rich soils, or junky nutrient poor soils, and everything in between. Soils in riverine valleys that receive the floods and muds of centuries tend to be on the rich side. Soils that are ancient and worn down from millennium of erosion tend to be on the poor side when it comes to basic nutrients.
PHOTOSYNTHESIS
Simple sugars made by the plant are glucose, composed of carbon, hydrogen, and oxygen. Sugars are inefficient to store, hence the plant converts them into carbo hydrate starches, oils, and fats. These are the seeds, grains, and fruits that we are familiar with: Oats, wheat, rye, rice, soy and corn. Coriander, pepper, nutmeg, cardamon. Olive oil, sunflower oil, canola oil, safflower oil. The same foodstuff we feed to our cows, pigs, chickens and sheep.
Plants combine sugars with nitrogen and sometimes sulfur atoms too, to make proteins like pinto beans, garbanzo beans, lentils, almonds, chia, walnuts, and broccoli. It also combines the carbon hydrogen oxygen with nitrogen to make alkaloids such as caffeine (coffee), nicotine (cigarettes), quinine (gin and tonic), mescaline (peyote or san pedro cactus), theobromine (chocolate), tubocurarine (blow dart poison and surgical anesthetic). Well you get the -ine idea of the alkaloids which are basic in pH and have a bitter taste.
Plants transform sugar molecules into plant hormone molecules. The plant hormones help the plant to grow roots, ripen up, elongate and develop, and enter or exit dormancy. In addition, plants make a wealth of other compounds useful as detergents, dyes, tanning agents, waxes, medicines. All of this from photosynthesis and from nutrients absorbed from the soil.
RESPIRATION
Respiration is what we all do, we breathe. Breathe in oxygen, exhale carbon dioxide. This is true for bacteria, bugs, worms, animal, people. This is not true for a group of bacteria which like to live in places with no oxygen at all, those are the anaerobic bacteria. The anaerobic bacteria thrived before plants took over and spewed tons of oxygen into the atmosphere. They did not like that. Nowadays these anaerobes are still ever present, but just not as dense or as visible. The best way to acknowledge their presence is to put some cut flowers in a vase and let the flowers sit. Let them sit until the flowers are all wilted and go brown. Let it sit for a few more days. Then go and smell the water inside the vase. There you go. Anaerobic bacteria eating the decaying plant matter. Yuck dump it!
Plants breathe in carbon dioxide and breathe out oxygen in photosynthesis. Plants can also breathe in oxygen and breathe out carbon dioxide when they are respiring, and using some of their stored energy to grow and develop. They are producers of food and oxygen, as well as consumers.
CYCLING OF PHOTOSYNTHESIS AND RESPIRATION
Photosynthesis is like – a gain, you are making food and storing it. Respiration is a minus, you are spending the energy. As a plant, if you spend more than you make bad news, you get stressed, and go dormant or die. Your balance, going forward, must be positive.
WATER AND NUTRIENT UPTAKE
A nutrient like calcium is present in the soil as whitish chunks of rock or tiny bits of dust. Nutrients like magnesium iron zinc potassium and copper are metals that are present in the soil bound up in some mineral chunks, or present as a crystalline solid by themselves in a vein. When water comes along it dissolves these substances and they become a part of the water flowing through the pores of the soil. The plant roots are turning this way and that way, digging with the lubricating goop tip of the root cap, while the root hairs spread out to suck up any available water. There is an exchange of electrical ion activity at the root zone and the nutrients are pulled and start going up up up into plant.
TRANSPIRATION
The movement of water up the stem or trunk of a plant is similar to you sucking on a straw at the milkshake in a cup. Or, it is like trying to siphon gas by sucking through a plastic tube. In a plant it is the leaves with the stomata open, breathing, that sets in motion the movement of water up up up. Imagine that the sun is out, theres tons of water in the soil, and your energy factory (the leaves) is in full swing. So bring up that water, breathe in that carbon dioxide through the stomata, and make food make food make food! Move it! Store it! More food more food! When the sun is not shining, then the stomata are closed and so is the energy factory. Time to rest.
TRANSLOCATION
Plants need particular compounds in particular places at various times in their development. When it is actively growing green leaves, the plant needs nitrogen for those new sprouts. And if nitrogen is in short supply, the plant will move it from the older leaves to the younger leaves. If it is in really really short supply, that is when you will see stunted plants or leaves going yellow green in color.
PLANT DEVELOPMENT
In general we divide a plant’s development into two phases – the vegetative phase of getting bigger and growing a lot of leaves, and then the reproductive phase of flowering, fruiting, and dispersing of seeds. This can happen very quickly on a one time basis for annual plants that live a few months. Boom and bust. In a long lived plant the phases alternate back and forth, back and forth. And if the conditions are not ideal the plant will sometimes skip the reproductive phase and hang out until the conditions are right. Or they may give a a one last hurrah and just all in, go for it, but then die afterwards. These phases often coincide with planetary cycles of warm and cool or wet and dry.
Mission Azul 