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Mycorrhizal Fungi in Hydroponics

By     22 October 2018 


Q. I already use Trichoderma. Are mycorrhizal fungi any different?

Both are beneficial fungi found naturally in soil. Trichoderma are more for cycling nutrients in the soil and providing protection against soil pests (but you will seldom find it labeled as a pest control) while mycorrhizal fungi help more with nutrient and water uptake and increased root growth. Both combined will promote a very healthy root system overall.The two work together well. Trichoderma help make nutrients soluble. Mycorrhizal fungi can actually take the nutrients up and translocate them into the plant.


Q. How do I successfully introduce and propagate mycorrhizal fungi in my hydroponic garden?

Mycorrhizal fungi can be mixed directly with soil-less media or added to the nutrient solution directly just like any regular powder supplement. There is a myth that you cannot use mycorrhizal fungi with synthetic / mineral-based nutrients, but this is not true. Mycorrhizal fungi can be used with soil, hydroponics and cuttings. The key benefits in hydroponics are extended root systems (which naturally lead to an increase in yield), not to mention protection against root zone pests and diseases. Imagine miles of mycorrhizae hyphae exploring the nutrient resources. Mycorrhizal fungi cause roots to branch and form more fine feeder roots that can go after nutrients and minerals.


Q. Should I feed mycorrhizae carbs? (e.g. molasses?)

Molasses and other carbs are good for feeding bacteria and other types of fungi. But you don't need to feed the mycorrhizae. That's missing the point. The plant feeds them! It's the exudates from the plant roots that cause the mycorrhizal propagules to germinate. (There are synthetic compounds that cause the mycorrhizae to germinate but they are unnatural, expensive and not commonly available.) You are better off adding products which contain humic acids (organic growers can use high quality organic inputs such as North Atlantic sea kelp) to promote more root exudates (food for the mycorrhizae).


Q. What hydroponic growth media do mycorrhizae prefer?

Mycorrhizal fungi can create mycelial networks in soil, coco coir, rockwool and many other inert growth media. They can even survive in a totally aqueous environment, as long as it is properly aerated, but they will not replicate. Mycorrhizae will grow and increase in biomass only once they are attached to a plant root.


Q. What about mycorrhizal fungi and high phosphorus levels?

Mycorrhizae fungi spores 'sleep' while levels of phosphorus are high (above 70ppm). They only awaken when levels drop lower than this. This is another reason to establish your mycorrhizae as early on in the plant's development cycle as possible.


Q. What conditions do mycorrhizal fungi prefer?

Temperature: around 68-73°F is ideal but mycorrhizae can also help your plants tolerate occasional temp extremes.

Moisture: mycorrhizal fungi like to have a good air/water mix to thrive. Too moist or too dry is not ideal. Once again, they will help the plant tolerate any extremes that occur.

pH: it depends on the mycorrhizae species but generally they thrive in 5.5-7.5. Some can tolerate acidic conditions better than others while some like alkaline better than others. Look for products that are made from a blend of different species in order to create a healthy mycorrhizae population that will thrive in varying pH conditions.


Q. What conditions should be avoided?

Very high temperatures. (135- 140°F will definitely start killing them off but then, at those temperatures, the happiness of your fungi is the least of your problems!) The less chlorine your water contains, the better for both fungi and plants too. However, typical levels of chlorine from municipal supplies should not cause a problem.


Q. When should I start using mycorrhizal fungi?

As soon as possible! It takes less mycorrhizae to colonize a juvenile plant than a larger one. Commercial growers have negated the cost of mycorrhizal fungi with their increased seed germination rates. It takes a couple of weeks to form on the roots after the first inoculation so get the process started right at the seedling / cutting stage. The trick is to introduce the mycorrhizal fungi spores as early as possible to give them time to establish themselves. This is particularly important if you are growing short-cycle plants.


Q. Do mycorrhizal fungi need to be reintroduced on a regular basis? Do I need to add it more frequently than once with every nutrient change?

Best performance is achieved with numerous applications throughout the growth cycle. You can't really overdo mycorrhizae. If there are more roots producing more exudates it will probably help to add more mycorrhizae. But don't bother any later than 2-3 weeks before harvest. It's a waste of time. Your mycelial network should already be established. It won't do any harm to keep using it (and often the instructions on the mycorrhizae product will encourage you to!), but you're just wasting your money! Adding it with every nutrient change won't do any harm either. It's just a question of minimizing waste. A good tip is to mix the fungi in a one gallon jug to get it nicely diluted, then pour it into your nutrient solution. Otherwise the powder can sit at the bottom of the res. The white powder you sometimes see at the bottom of your res is just the carrying agent of the spores, not the spores themselves.


Q. What mycorrhizae products can I find in my local grow store?

You'd best ask down at your store! You'll most likely find a few different brands. The products usually come as a jar of white powder - this is a 'carrying agent' for the spores. If you want to compare products, look for the number of mycorrhizal species per pound and the diversity of species. Oh, and the price!


Q. Ok, but how do I actually use mycorrhizal fungi to benefit my plants?

Mycorrhizal application is easy and requires no special equipment. The goal is to create physical contact between the mycorrhizal inoculant and the plant root. Mycorrhizal inoculant can be sprinkled onto roots during transplanting, worked into seed beds, blended into loose growth media, "watered in" via existing irrigation systems, added directly to the nutrient solution, applied as a root dip gel or even probed into the root zone of existing plants. Most hydroponic growers simply add the fungi by diluting the powder holding the spores into some water and adding this to their nutrient solution. It's very easy.


Q. Do mycorrhizal fungi actually guard the roots against other nasties? If so, which nasties exactly?

Yes. Nasties include: rhizoctonia, fusarium, pythium and phytophthora. They can also mitigate the detrimental effects of high salt conditions.


Q. How exactly do mycorrhizal fungi guard the roots? Do they simply "crowd out" the root zone or is it more complex?

Endo mycorrhizal fungi thicken the cell walls around the root cortex making it harder for pathogens to penetrate. They also compete with pathogens for some of the same food sources. Mycorrhizal fungi help with antibiotic production, armoring of roots with chitin, and control of excess nutrients.


Q. What's the difference between "endo" and "ecto" mycorrhizal fungi?

Endo = has an exchange mechanism inside the root (and hyphae extends outside of the root). Ecto= lives only outside the root. The endo mycorrhizae form with mostly green, leafy plants and most commercially produced plants. Ecto mycorrhizae form with mainly conifers and oaks: more woody plants. Endos are for everything else. In hydroponics, ectos don't even matter. Fruits, veg, flowers ... stuff we love to grow ... they love endo.


Q. Are there any differences in how the hydroponic grower should use mycorrhizal fungi compared with the organic grower?

Both types of grower need to get the inoculum near roots. Same product, same application rates. Same number of spores per square foot. Both types of growers can reduce their nitrogen and phosphorus inputs.


Q. Do mycorrhizal fungi help with nutrient extraction in a hydroponic environment or are they more relevant in soil / organics where nutrients need to be broken down first in order to become available?

Mycorrhizal fungi are just as effective in hydroponic applications as they are in organics / soil. A main function of mycorrhizal fungi is phosphorus uptake. It's important to have a good colonization and a good mycorrhizal fungi "web" already established before you go into flowering.