We’ve all heard the fables of salting an enemy’s fields, and those who are the salt of the earth are often near and dear to us, but what does salt in garden soil do to the plants that live there? What is salt?
Most people think of salt as the ‘and pepper’ variety. Table salt (NaCl) is the crystalized form of equal parts sodium (Na) and chlorine (Cl). Salt is necessary for human life and we’ve been processing it for over 8,000 years. In fact, as Roman Legions were sometimes paid a salt stipend (salarium), the word evolved into “salary”. But in the garden, salt is more of a chemistry class than a history class. Chemically, a salt is any compound that is formed when an acid reacts with a base, bumping all or part of the acid’s hydrogen atoms off and replacing them with a metal or other cation. This neutralizes the acid. [Don’t panic - keep reading] Chemistry 101: anions & cations In case it’s been too long (or never) since you had a chemistry class, everything is made up of atoms. Atoms have a nucleus with neutral neutron(s) and positively charged proton(s) and negatively charged electrons flinging themselves in semi-orbit around the nucleus. If the number of protons and electrons are equal, the atom is stable. If an electron gets bumped out of orbit, the atom becomes positively charged and it is called a cation [KAT-i-on]. If an extra electron is lured into orbit, the atom becomes negatively charged and it is called an anion [AN-i-on]. The reason this is important to gardeners is because the electrical charge of the atoms and molecules that make up the soil determine how many nutrients are available to plants. This is called the Cation Exchange Capacity. Salts in the soil There are many ways salt can make its way into garden soil. Ocean breezes, de-icing and over-fertilizing can all cause salinity levels to rise. Drought is another major factor in soil salinity. As ground water reserves are depleted, the mineral content increases and that means more salt. Ammonium and nitrate are excellent sources of nitrogen and they are commonly found in fertilizers in salt form. Gypsum and lime also contain salts. Normally, salts are leached out of the soil by rain and carried below the level of most plant roots, but not always. Plant reactions to salt Normal healthy soil contains many dissolved salts. These include:
As plants absorb water and nutrients through their roots, the water extraction can increase salt levels in the soil. Salt in the soil can stress plants, reducing root growth. If too much salt is absorbed, the plant is unable to perform photosynthesis and it will die. This is because of osmosis. Osmosis is the process by which a liquid (water) flows through a semipermeable membrane. Minerals (solutes) held in that water, and their electrical charges, pull water across the membrane, from areas of low mineral concentration to areas of high concentration. When this happens in plants, the sugars and organic compounds normally found in plant cells attract water from the soil and pull it into the plant, along with important nutrients. When there is too much salt in the soil, this process is reversed and plants are deprived of important nutrients and water. Too much salt in soil can also lead to other elements, such as boron (B) reaching toxic levels. Symptoms of this toxicity include burnt-looking leaf edges, especially in older leaves, yellow streaking, and wilting. [I learned that the hard way when I watered my house plants with a batch of brine shrimp that died overnight. I lost over 180 of my 210 plants.] To prevent excess salt in the garden, minimize the use of chemical fertilizers during drought and use rain barrels to collect low-salt rain water. Water from rain barrels can help offset the higher salt levels found in tap water.
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The crisp, slender stalks of scallions are easy to grow and they take up very little space in a garden or on a windowsill. Scallions, also known as green onions or spring onions, can either be immature onions before they set bulbs (spring onions), or a specific variety of Allium that never forms significant bulbs. Scallions in the garden
Scallions can be grown in window boxes, indoor planting containers, hanging planters, or in the ground. They can be grown in full sun or used in shade gardening. The spiky forms of newly growing scallions add a pretty accent to many plantings. How to grow scallions Seeds can be started at any time of year and seedlings can be grown indoors or out. Seeds should be heavily planted, 1/2" deep. Scallions can grown in clumps, so there is no need to thin transplants. Scallion seeds require moisture to germinate and they can take a month to get started. Keep the soil moist and be patient. Like other onions, scallions have a shallow root system, so proper irrigation and frequent, gentle weeding are important. Scallions are heavy nitrogen feeders, so feed regularly with fish emulsion, blood meal, or alfalfa meal. Planting a new batch of scallion seeds every three weeks will keep you supplied with scallions year round. Also, each time you snip the base off of a scallion, those roots can be replanted to grow a new scallion! Scallion pests and diseases Scallions may be attacked by thrips. Thrip damage gives the leaves a white streaked look. Thrips can be reduced by spraying plants with soapy water. If tunnels are found in the underground portion of the plant, it may be onion maggots. Most members of the onion family are susceptible to onion white rot and other fungal diseases, such as onion rust. If nematodes are feeding on the root system, plants will appear stunted or deformed. Onions left in the refrigerator for too long often exhibit a fuzzy white growth around the roots. Those onions have a fungal disease, onion white rot. Keep them from coming into contact with anything related to your garden. Onion white rot lifecycle
Sclerotium cepivorum fungi strike onions, garlic, and other Alliums. Onion white rot can stay viable in the soil for over 20 years. Unlike other fungi, this one does not produce spores. Instead, it survives in the soil as sclerotia (dormant fungal structures with stored food). These sclerotia can travel by piggybacking on equipment, people, tools, plants, and wind. A single sclerotium in 20 pounds of soil will infect nearby plants. One or two sclerotia in one pound of planting soil will cause all plants to be infected. The sclerotia will stay dormant in the soil until Allium comes on the scene. As part of their growth, these plants discharge certain chemicals into the soil around their roots. These chemicals stimulate the fungi to germinate. Soil temperatures of 50° to 75°F allow the fungi to grow, peaking between 60° to 65°F. Onion white rot symptoms Onion white rot first appears as a cottony growth around the base and sides of onion or garlic. These fungal mycelia are vegetative growths that become compacted. These poppy seed-sized black spots are visible to the naked eye. Other signs of infection are yellowing lower leaves, wilting, and leaf dieback. Older leaves will begin to rot at the base, and roots will decay, making it easy to pull infected plants from the soil. Host plants die soon after infection. Onion white rot travels sideways, from plant to plant, using intertwined roots as a pathway. This problem thrives in cool, damp soil. Onion white rot control This disease is persistent in the soil. And there are no known chemical controls. Once an infection has occurred, sanitize all tools and equipment that may have come into contact with it and avoid planting Alliums in that location for at least 8 - 10 years. If that is not an option, starting onions from seeds rather than sets (transplants) may help. The seeds will have minimal root growth while the fungus is most active. Onions grown from seed take two seasons to mature, so the problem may not be avoided entirely. Also, spacing onions 12 or more inches apart may halt the spread of this fungus. You may be able to save some of your onions with deficit irrigation. Leeks are the least susceptible members of the Allium family. Due to the direct link between onion and garlic chemical exudates and fungal germination, research is underway to see if applying Allium plant hormones to infected soil without a host crop might trick the sclerotia into germinating when there is no food for them. Since this is not an option for the home gardener, prevention is the best bet. Plant only certified pathogen-free onion sets and garlic cloves to avoid infecting your soil with white onion rot. Since onions and garlic purchased from grocery stores are not guaranteed pathogen-free, keep them out of the garden and the compost pile. |
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