Organic Growing Techniques

In Deep: Slightly Nerdy Questions on Organic Gardening

Dr Carole Rollins and Dr Elaine Ingham answer any organic growing question we can throw at them! Don't forget to add your own below!

Q) Can you use organic and mineral-based (aka chemical) fertilizers together? Do mineral-based fertilizers damage soil microbiology?

A) Yes, you can use them together. There are also many plant food products available that contain both organic and mineral-based ingredients. Organic acids such as humates can provide substantial benefits to mineral nutrients. Organic elements can enhance mineral based nutrients and vice versa.

When it comes to soil microbiology, mineral-based nutrients can cause problems. Soluble phosphorus can inhibit many strains of mycorrhizae, while abundant nitrogen will cause nitrogen-fixing bacteria to become dormant.

Q) Can I use organic nutrients in a soilless mix? Is it possible to cultivate beneficial microorganisms (like those you find in soil) in a soilless medium?

A) Organic nutrients can work well in soilless media. Try mixing in powder or granular organic nutrients with your medium. You can cultivate microbes in a soilless medium but it is difficult to find balance and ensure long-term survival.

Q) What is the difference between fungi and bacteria?

They are both exceptionally important in the ecosystem, as they both help in decomposition, but they are quite different. Bacteria are unicellular organisms that can rapidly colonize localized areas in soils. Fungi are multi-cellular and slower growing so apply them as soon as possible. What’s more, bacteria can thrive in disturbed soils, but generally fungi can’t as soil disturbances interfere with their mycelia networks. In many cases bacteria and fungi compete, but they can both exist together in a balanced system. Both types of organisms secrete various byproducts such as organic acids that can be exceptionally beneficial to your plants. As with any microbial option, be sure to understand why you are choosing and applying the organism you have selected for use.

Q) Should I use carbohydrates to feed my beneficial? How can carbs help plants?

Feeding beneficials with simple sugars sounds good in theory but in practice it can cause headaches. When bacteria are exposed to high levels of sugar they begin to frenzy (a desired effect within a high oxygen aerobic compost tea system). The unfortunate problem with this activity is that most beneficial bacteria are aerobic. Aerobic organisms use oxygen during activity. In the root zone where oxygen levels are at a premium, does this type of stimulation make sense or could it lead to anaerobic conditions? Not to suggest the abandonment of a carbohydrate supplement, simply be aware that this reaction can have a negative effect on plant roots and cause a proliferation of pathenogenic microbes stimulated by the lack of oxygen. Sometimes a little is better than a lot. To benefit microbes, consider insoluble humates or substances like Biochar as more persistent sources of carbon.

Q) Can one type of beneficial be too aggressive and will it crowd out other species? Isn’t it all about variety?

In a natural system, biodiversity is the essence of life. Remember that bacteria can colonize more quickly than most types of beneficial fungi so it’s easier to find benefits from bacteria in short-cycled, annual crops. In nature most established ecosystems are usually fungal dominated, however these systems have evolved and been left to mature for exceptionally long periods of time.

Q) What are the benchmarks for a good quality compost tea and what are the scope and limits of its use?

There are several professional organizations that provide standards and testing for microbial diversity in compost tea. If you are serious about this beneficial organic option be sure to get your solution tested so you can be sure it truly is beneficial. There is clearly no way to visually assess a compost tea and if it is untested you will have no idea what is going into your soil. A quality compost tea blend is an excellent biological inoculant and in some cases could be effective as a foliar spray for disease prevention. Note: it is far easier to amplify bacterial populations in a short-cycled compost tea brewer, but you can still charge your medium with many other soil dwelling organisms when applying your brew.

Q) How do plants extract the nutrients they need from soil?

A: Plants need different things at different times in their life. As such they work in partnership with a huge variety of microbes in the soil – feeding various microbes in return for different nutritional elements. Plants can control which nutrients are available by altering the pH around their roots.

Q: So what if the plant needs more nitrate, for example? (These require alkaline conditions for maximum absorption.) How does a plant go about creating more alkaline conditions and thus nitrate around its roots?

A: Plants create sugars that encourage the development of certain alkaline-producing bacteria. An abundance of these bacteria create the necessary pH shift.

Q: So plant roots directly feed soil microbiology?

A: Pretty much all organisms around the roots rely on the plant for food in one way or another. Additional foods that help supplement what the plant directly provides are contained in general organic matter.

Q: If it’s all going on in the soil anyway, why do gardeners brew compost tea?

A: Compost tea supplements the micro-organisms that are missing from your soil or plant surfaces, and to add additional foods so those organisms have something to eat when the plant isn’t specifically feeding them.

Q: What exactly is compost?

A: Compost is the mix of plant materials, the more kinds the better as it produces greater diversity of microbes.

Q: Is sea kelp an organic fertilizer?

A: First, what do you call an “organic fertilizer?” It is perhaps more accurate to speak of “organic inputs” rather than “organic fertilizer” as the latter tends to imply minerals to many gardeners. As for kelp, it has not been through the composting process so it cannot be labeled compost—it has simply been dried and ground up. It contains many plant nutrients, whatever happened to be in the kelp as it was growing. Thus it can best be considered an organic input.

Q: So kelp contains plant nutrients. But how do plants access these nutrients?

A: Bacteria and fungi first need to decompose the kelp. Then these bacteria and fungi need to be consumed by protozoa, nematodes and microarthropods in order to release the nutrients in a plant usable form. That's what is going on in a composting process.

Thanks to Drs. Carole Rollins and Elaine Ingham for their answers!

Add your own question below!