Kelp is a popular plant additive and understanding what it is and how it benefits plants can help a gardener make the best use of it.
Kelp (seaweed) are types of algae that resemble underwater plants. Much like vascular terrestrial (land) plants they grow in plant-like structures, use photosynthesis, and absorb nutrients through a nutrient solution (the seawater they are submerged in). Compared to a plant; a kelp thallus has fronds or blades instead of leaves, a stipe instead of a stem, and a holdfast instead of roots, and their internal structure is much simpler and less specialized. The holdfast (literally “hold fast”) of a kelp plant is only used to anchor the plant in place, and nutrients are absorbed through the fronds (leaf analogs).
Kelp forests supply food and protection for a wide variety of species, and the health of the forest is reflected in the health of the creatures that live on and around it.
Because kelp relies on photosynthesis, it only grows in nutrient rich water shallow enough to receive needed light (depths of less than 100 feet or so). Kelp is primarily found along the coastlines of temperate oceans. One common Atlantic kelp is named Ascophyllum nodosum which is a brown algae kelp that uses air bladders to maintain the buoyancy of the upwardly growing stipes. This kelp is one frequently used as a plant nutrient source.
Kelp forests supply food and protection for a wide variety of species, and the health of the forest is reflected in the health of the creatures that live on and around it. Sea urchins are herbivores that graze on debris from the forest, and predators such as sea otters eat the sea urchins. If the predator is removed (such as when sea otters are over hunted by people) then the sea urchins will overpopulate and graze on the kelp holdfasts, unanchoring the kelp. If left unchecked long enough, the urchin population will destroy the kelp faster than the kelp can repopulate, eventually converting the forest into an urchin barren (a sea desert with sea urchins but without kelp).
Fortunately, kelp grows fast, and popular varieties can be farmed. The tops of ascophyllum nodosum can be harvested and it will regrow from the holdfast and remaining stipe, allowing for many harvestings from the same kelp if allowed to regrow between harvests. Modern kelp farming techniques use mechanical harvesters that intentionally leave a substantial portion behind so the same area can regenerate and be re-harvested as soon as the following year. This practice is both more sustainable and productive than the previous hand harvest method which had more in common with the urchin mentality of leaving little behind for later until nothing is left.
Kelp plants feed by drawing nutrients out of the seawater they are submerged in. If they were true plants they would be the ultimate foliar feeders, as not only do they absorb their nutrient solution through their fronds, but tolerate being submerged and left in their nutrient solution as an application method. As the kelp draws nutrients from the seawater into itself, it helps purify the water. If the kelp is removed, it is itself a source of the nutrients it has collected, much in the same way terrestrial plants can be a source of nutrition for other terrestrial plants through grinding into meals or composting. The harvested kelp can be processed and used to feed garden plants.
Kelp doesn’t have high concentrations of nitrogen, phosphorus or potassium, and is generally not used as a major source of those plant nutrients. It does however have a wide spectrum of micronutrients and some key growth hormones which contribute to its reputation as a superior general plant tonic.
Since kelp supplies a small amount of many micronutrients it can be used to prevent or correct a variety of different micronutrient deficiencies. If a micronutrient deficiency is suspected, an application of kelp may well correct it even if the particular deficiency is undiagnosed, and including kelp in a feeding regimen may well prevent such deficiencies from happening in the first place. Many plant processes rely on trace amounts of micronutrients to act as catalysts for chemical reactions. Only a trace amount is needed since catalysts are not used up by their reactions, and kelp is a trace source of many needed catalysts. Kelp also contains amino acids which help chelate these micronutrients into forms available to plants.
Kelp is also a source of cytokinins (CK) which are are plant hormones that promote cell division in growing shoots. Added to the soil or sprayed on the plants, cytokinins help the plant make efficient use of existing nutrients and water in drought conditions. A low ratio of auxins (root growth hormones) to cytokinins (cell growth hormones) stimulates and promotes tip and shoot formation. Kelp has both auxins and cytokinins, but generally in a ratio that favors the cytokinins.
Another hormone found in kelp is gibberellin (also known as gibberellic acid or GA), which encourage stem growth and elongation. At high concentrations gibberellin can be used to encourage germination of seeds or manipulate gender expression, but at the levels found in kelp it is generally considered a growth stimulant.
Kelp has been used to improve plant growth for so long the origin is lost to history, but as understanding of how it helps improves, so does the ability to use it best.
“Root rot” is a generic term encompassing any number of soil-inhabiting fungi, or fungi-like organisms that ultimately (and usually quickly) cause the collapse of a plant’s root system. It is a disease that thrives when soils are moist, poorly drained and depending on the particular pathogen, the appropriate temperature to “set up shop.” It often occurs in plants that have a high level of salts from over-fertilization.
There are several symptoms of root rot and many can often be mistaken for nutrient deficiencies or temperature extremes.
The most common types of root rot pathogens are Thielaviopsis, Fusarium, Rhizoctonia, Pythium and Phytopthora. Pythium and Phytopthora are not true fungi, but rather organisms that behave like fungi. This is relevant when seeking treatment options. These are not however the only pathogens that cause root rot. Precise identification is not always important, so long as the conditions that favor disease have been corrected and all of the affected plant material has been removed. If a positive identification of a particular pathogen is required, the diseased plant may be sent to a lab for analysis. Contact your local cooperative extension to learn where the appropriate plant tissue lab is located in your state.
Signs/Symptoms of Root Rot
There are several symptoms of root rot and many can often be mistaken for nutrient deficiencies or temperature extremes. Though there are several fungal pathogens that cause root rot, the symptoms of them are all very similar. Plants displaying signs of root rot are usually wilted and fail to “bounce back” after irrigation. Plants will often appear to be stunted and show no signs of new growth. Leaves, often lower ones, will yellow and may drop off. This is due to the plant’s inability to properly absorb water and nutrients.
If any of these symptoms are noticed, it is important to check the roots. Root systems of healthy plants are usually white or light colored and fibrous, or possess a robust network of large and small tendril-like appendages. Roots that have succumbed to fungal pathogens are brown, often “mushy” and may appear stunted. Fungal pathogens enter through a plant’s feeder roots and then spread throughout the entire root system. This process can occur in as quickly as a few days to a week, or longer. The amount of pathogen, health of the plant, soil moisture and temperature combinations affect the speed of transmission.
How to Treat it
The short answer to this question is, “you don’t.” In the vast majority of cases, once you have observed the foliar symptoms of root rot, it is generally too late to do anything about it. On the outside chance that the early stages of root rot have been observed, there is hope that the affected plant can be nursed back to health.
Remove the plant from the soil and container. Make sure to dispose of all of the soil and prune off as much of the diseased root system as possible. If possible, transplant into a new container. If reusing the old container is the only option, make sure to thoroughly disinfect it with a bleach solution or equivalent such as H2O2. A solution of one part bleach to nine parts water is sufficient to kill pathogens. Make sure that the entire container can be submerged in the solution and allow it to soak for no less than 30 minutes.
When replanting salvageable plants, make sure that the media is clean. If planting back into a soilless media, ensure that it was pasteurized or treated with heat before being sold. If the plants are to go into a hydroponics application, make sure that all of the water has been drained from the system and that clean water with hydrogen peroxide or an equivalent product has been cycled through repeatedly. If plants are to be replanted into the ground, make sure that enough of the contaminated soil has been removed and that the replacement soil has sufficient drainage.
There are available fungicides designed to treat or control root rots. Often though, the disease is discovered after treatment is a viable option. If a fungicide is sought, proper identification of the pathogen is a must and make sure to examine the label carefully. Since Pythium and Phytopthora are not true fungi, not all fungicides will control them; conversely a pesticide designed to control Pythium or Phytopthera, may be impotent when used to fight Thielaviopsis, Fusarium, or Rhizoctonia.
How to Prevent it
Preventing root rot is far easier and a more effective approach than trying to combat it once it has taken hold of your plant’s root system. Overwatering is the most common cause of root rot. Allowing soils to dry out between waterings will go a long way to prevent fungal pathogens. Improving your soil media’s drainage will also help if this is feasible. Selecting an appropriate media for the types of plants or crops you wish to grow will also help reduce the risk of root rot as these soils should contain a proper balance of large and small particles to allow for proper drainage.
Ample light and ventilation will also help to reduce the incidence of root rot. Make sure that your plants receive enough natural or artificial light and air exchange so that excess moisture can be evaporated or dry up before it sets the stage for the introduction of fungal pests. Don’t over-crowd your plants; plan for them to grow. Do this by spacing them far enough apart so that they receive ample air circulation or thin those out once they start to grow into each other.
Avoid over-fertilization of your plants. Too much fertilizer will inhibit your plants’ natural defenses against diseases. Too high a fertilizer value will also burn root tips, which become easy access points for pathogens to avail themselves of. As with any soil amendment, pesticide or fertilizer, make sure to use no more than the manufacturer’s recommendations. When it comes to pesticide use, this is not only best practice, it is also the law.
Finally, make sure to never re-use soil media that has been infected with any pathogen, fungal or otherwise. Hygienic growing practices require the use of new soil with any new planting or transplanting, but on occasion (or frequently) we have all reused soil out of necessity. If soil needs to be re-used, make sure that it has only been in contact with healthy plants.
So after the first Soil Blog post, I was all excited telling a friend of mine about having started the blog, and how I have a bunch of different ideas, and blah, blah, blah. After I was done, he asked a question “Is soil just dirt, right?”
That little exchange has become the inspiration for this post because like you guys, I want to become a better grower. To do that I think we really have to understand what we are working with, and how any changes we make to our soils will impact plant growth.
Like soil, dirt can also have air, water, and minerals but without bacteria, fungi, and organic matter, water will not be trapped in the dirt and plants can’t grow.
In my first post I went on for a bit about soil pH and its impact on bacterial and fungal growth, but I never clearly defined the term soil. Generally speaking, soil contains living organisms (bacteria, fungi, earthworms etc.) and decomposing organic matter while dirt does not. The presence of both living organisms and organic matter are essential for plant growth. Topsoil, or the uppermost outer layer of soil, usually has the most organic matter, and this is where most plants have their roots. In addition to organic matter, soils also contain air, water, and minerals. There are a few soil classification systems that exist to describe different types of soils and dirt. The United States Department of Agriculture (USDA) has 12 different soils classifications, which they describe on their The Twelve Orders of Soil Taxonomy page. Since we all live in different places, our soils will have different classifications, but you should definitely find out what soil types are in your area.
Like soil, dirt can also have air, water, and minerals but without bacteria, fungi, and organic matter, water will not be trapped in the dirt and plants can’t grow. Growers can turn dirt into soil by mixing it with compost, which is just decaying organic matter. Instead of compost, peat moss can also be used. Peat mosses sold in stores are the dried decaying remains of mosses that grow in water-rich environments known as peat bogs. While peat mosses are great for enriching dirt and soils, the harvesting of them is not considered sustainable. These mosses grow incredibly slowly, just a few millimeters per year, so too much peat moss harvesting can have long-term damaging effects on peat bogs.
Another alternative to composting besides peat moss is the use of coconut coir. Coconut coir comes from the inner shell of coconuts, and is produced as a waste product of coconut harvesting making it a renewable and more sustainable soil additive than peat moss. Coconut coir retains more moisture than peat moss, which means the soil will hold water better during plant development. Unlike peat moss, the addition of coconut coir doesn’t necessarily have to make your soil more acidic.
Coconut coir usually comes in three different forms, coco fiber, coco chips (croutons), or coco peat. Coco fiber and coco croutons are longer forms of the coir good for creating space to aerate soil. Since they also hold a large amount of water, they can retain nutrients dissolved in the water further contributing to plant health. By themselves coco fiber or coco croutons are inert, meaning they do not provide nutritional value to plants by themselves. Coco peat is not from a peat bog like peat moss. It’s called coco peat because it is sold in a similar form to peat moss, a dried brick. Coco peat is the ground up form for the coconut coir. This form can be added during composting which adds greater water retention to compost soils. Composts that include coco peat tend to have a lower pH, which is better for some plants. Coconut coir is usually in the pH range of 5.2 to 6.8. This is much closer to neutral than peat moss which has an acidic pH between 3.5 or 4.5. Using a substrate that is closer to neutral has many microbial benefits. One being an increase in microbial diversity, accompanied by a lower pathogenic fungi population. Pathogenic fungi prefer to grow in acidic soil conditions, ideally in a pH range of 3.0-5.0. As a result, this reduces the chances of your plants developing a disease. The fact that coco fiber retains a lot of water can modulate acidity, and is sustainable makes it a great soil additive.
So what do you think? Does coco coir sound like something to try in your garden?