Mycorrhizae for Succulents & Cacti? (Here’s the Evidence)

mycorrhizae and succulents and cacti

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Many gardeners like using a potting mix that carries mycorrhizal fungi.  Some may even like to use a soil inoculant with their succulents and cacti. 

Do mycorrhizal fungi also work with succulents and cacti?

Succulents and cacti benefit from mycorrhizal fungi with better uptake of nutrients, water, and carbon dioxide for photosynthesis. It improves the overall health of the plant with a bigger plant size, more roots, and longer roots.

In this article, we will give substantial evidence to show the benefits of mycorrhizal fungi on succulents and cacti.

How do mycorrhizae benefit succulents?

1. Increased nutrient uptake

Mycorrhizae can increase the nutrient uptake of succulents.

According to a study, Desert Agaves (Agave deserti Engelm) that were inoculated with mycorrhizhal fungi for 5 months were found to contain higher amounts of Phosphorus (P) and Zinc (Zn) than those without mycorrhizae (Cui and Nobel, 1992).   The fungi strains used were Glomus epigaeum and G. fasciculatum.

The higher amounts of P and Zn found in the inoculated succulents were due to the fungi’s ability to solubilize and absorb insoluble P and Zn in the soil, and pass it onto the plant.

Increased Phosphorus levels brought on by the mycorrhizae immensely benefit succulents as Phosphorus is a major plant nutrient and is needed for several processes like photosynthesis, cell division and development of new shoots, and seed/flower formation. Thus, by increasing the amount of phosphorus in the plant, the mycorrhizae improve the succulent’s overall growth.

2. Increased water uptake

The same study also found that mycorrhizae considerably increased the water uptake of succulents.

This is due to a network of hyphae (i.e. long, microscopic, hair-like structures) that colonize the roots of succulents, serving as secondary roots for the plant to branch out further into the soil. This secondary root system has immense benefits to the succulent as it greatly increases its ability to absorb water and nutrients, which in turn improves the plant’s growth.

By increasing the water uptake, the mycorrhizae keep the succulent healthy, prevent shriveled leaves, and increase drought resistance.

3. Increased carbon dioxide uptake

In addition to higher levels of nutrients and water, the experiment also showed a 19% increase of net carbon dioxide uptake for inoculated Agave compared to the uninoculated samples (Cui and Nobel, 1992).

An increased level of carbon dioxide is an indication of higher photosynthesis activity as the gas is stored in the CAM(Crassulacean Acid Metabolism) photosynthetic pathway for photosynthesis during the day. 

Higher photosynthesis activity invariably improves the plant’s growth, durability, and yield.

How do mycorrhizae benefit cacti?

For cacti, mycorrhizae not only improve water and nutrient uptake but also result in more and longer roots.

Mycorrhizae work in cacti the same way as succulents because all cacti are succulents, even though not all succulents are cacti. The fungi colonize the roots of a cactus and extend hyphae deep into the surrounding soil to pull nutrients and water to the cactus and improve its growth.

1. Higher nutrient uptake

In the same study as the Desert Agave, researchers treated Desert Barrel Cactus (Ferocactus acanthodes) and Barbary fig (Opuntia ficus-indica) with the same mixture of mycorrhizal fungi (Glomus epigaeum and G. fasciculatum).  After 5 months discovered higher amounts of P and Zn nutrients in the treated plants than the untreated ones, leading to visibly better growth of the inoculated cacti.

A similar result is found in studying the influence of several mycorrhizal fungi strains (Glomus albidum, G. diaphanum, and G. claroides) on Prickly-pear cactus (Opuntia albicarpa). It found that 7 months after inoculation, treated plants contained higher amounts of P and Zn than the uninoculated specimens.

2. More and longer roots

The study also revealed that inoculated Prickly-pear showed significantly better growth, having a 24% increase in the dry matter weight than the plants without mycorrhizae (Estrada-Luna and Davis 2001).

Similarly, a study in which seedlings of Indian comb cactus (Pachycereus pecten-aboriginum) were inoculated with arbuscular mycorrhizal fungi for 8 months found that the inoculated sample had considerably more dry matter, a higher quantity of roots, and longer roots than the non-inoculated ones (Rincon et al, 1993).

 Inoculated seedlingsNon-inoculated seedlings
Dry matter0.418 g0.169 g
Root/shoot ratio0.260.14
Root length0.65 mm/mg1.41 mm/mg
Source: Rincon et al. (1993)

These experiments show that mycorrhizal fungi benefit cacti, improving the growth and resilience of the plant by increasing their water and nutrient supplies.

Which fungi benefit succulents and cacti?

Arbuscular mycorrhizal fungi particularly the Glomus species are the most beneficial for succulents and cacti.  Some strains of Trichoderma fungi are also beneficial to succulents and cacti.

There are numerous species of fungi in the rhizosphere, but only a few are useful to succulents and cacti. For instance, ectomycorrhizal fungi like truffles do not form relationships with succulents and cacti and are therefore not beneficial. Additionally, some fungi such as Fusarium oxysporum are pathogens and can infect the plant with diseases.

Only Arbuscular mycorrhizal fungi such as Glomus species and Trichoderma species benefit cacti and succulents by forming symbiotic relationships with the plant where they help the plant, in exchange for excess sugars found in the roots.

There are around 85 species in the Glomus genus, and all of them can form symbiotic relationships with succulents and cacti but some of the most widely known ones, which have been proven to benefit cacti and succulents include:

  • Glomus epigaeum
  • Glomus fasciculatum
  • Glomus albidum
  • Glomus calories
  • Glomus diaphanum

These fungi help succulents by sending out long strands of hyphae that can solubilize nutrients for the plant, and also reach farther into the soil to absorb more water and nutrients for the plant, leading to better growth and resilience.

Trichoderma is another genus of fungi that can be beneficial to succulents. There are an estimated 80 species in this genus, but the most widely studied and approved species for plants including succulents and cacti are:

  • Trichoderma harzianum
  • Trichoderma viride

Unlike Glomus species that provide more nutrients and water, Trichoderma benefits the plant by acting as biological control of pathogens in the soil such as phythum, keeping the succulent healthy by preventing diseases and infections.

Trichoderma can also work in cooperation with mycorrhizae, to improve nutrient uptake, and can stimulate growth.

A study of 3 different species of the Kalanchoe succulent (Kalanchoe pinnata, Kalanchoe tubiflora, and Kalanchoe gastonis-bonnieri) inoculated with Trichoderma viride showed that after 6 months, all plants treated with the fungi had taller growth, increased number of leaves per plant, bigger roots, and more new shoots compared to the untreated plants. The results also showed a marked decrease in mortality due to pythium (Prisa, 2020)

How to apply mycorrhizae to succulents and cacti?

You can apply mycorrhizal fungi by watering it down into the soil, applying it to the root ball, and adding it to the transplant hole.

Mycorrhizae is most effective when it is in direct contact with the roots of the succulent.  This can quickly infect the roots and start sending out the hyphae that do the magic.

The method of application depends on the age and size of the succulent or cacti.  It could be sprinkled on the root ball, mixed in with the soil/growing media, or mixed with irrigation water.

  • Sprinkle on the root ball

This method of applying mycorrhizae is best used when transplanting seedlings or repotting the succulent.

First, remove as much soil as you can safely remove from the root ball, then sprinkle a generous amount of mycorrhizae to the sides, top, and base of the root ball before putting it in the new soil.

  • Mix with soil

This second method of applying mycorrhizae is also suitable when transplanting or repotting succulents and cacti.

Dust the sides and bottom of the transplant/repotting hole, then put the plant inside. But be sure to remove excess soil on the root ball, before transferring the plant into the new hole, this will ensure that the roots are in direct contact with the mycorrhizae.

  • Mix with irrigation water

The final method of applying mycorrhizae to succulents and cacti is by mixing a water-soluble mycorrhizae product with the irrigation water, then using the mixture to water the plant.

This method will work in virtually all cases, and can even be used for fully-grown cacti that are several feet tall. However, with fully grown and established cacti, simply watering the surface of the soil is not very effective, as the roots are farther below, and the soil might not be very porous.

In such cases it’s best to make a series of narrow but deep holes around the root zone of the plant and pour the solution in, thereby increasing the chances of the fungi getting to the roots.

How long do the mycorrhizal fungi stay viable?

Mycorrhizae is good for cacti and succulents as long as it is viable. Generally, mycorrhizae can stay viable for about two years before losing viability, but any succulents or cacti that get colonized within this period will remain infected for the entire duration of their life cycle.

Mycorrhizae spores are quite durable, and most products will last for at least 2 years in the absence of plant roots before gradually losing viability. They are unaffected by cold temperatures or soil Ph, and only temperatures above 140 Fahrenheit (60 Celcius) will kill them.

However, if the mycorrhizae come in contact with plant roots, they germinate and colonize the roots, will remain in the plant for as long as it lives, and can remain in the soil for a couple of weeks after the plant dies or is removed.

If another cactus is placed in the soil within this time, the new plant will become colonized by the mycorrhizae.

Happy gardening!

Related

 Top 3 Inoculants for Plants: More Than Just Mycorrhizae

Top 8 Soil Inoculants for Plants (Editor’s Picks)

References

Cui, M., & Nobel, P. S. (1992). Nutrient status, water uptake and gas exchange for three desert succulents infected with mycorrhizal fungi. New Phytologist, 122(4), 643–649. https://doi.org/10.1111/j.1469-8137.1992.tb00092.x

Domenico Prisa. (2020). Trichoderma viride inoculated in the growing medium for the vitamin C increase in the leaves of Kalanchoe spp. and defense against Pythium sp. GSC Advanced Research and Reviews, 5(2), 089–096. https://doi.org/10.30574/gscarr.2020.5.2.0108

Rincón, E., Huante, P., & Ramírez, Y. (1993). Influence of vesicular-arbuscular mycorrhizae on biomass production by the cactus Pachycereus pecten-aboriginum. Mycorrhiza, 3(2), 79–81. https://doi.org/10.1007/bf00210697

Estrada-Luna, A. A., & Davies, F. T. (2001). Mycorrhizal fungi enhance growth and nutrient uptake of prickly-pear cactus (Opuntia albicarpaScheinvar ‘Reyna’) plantlets after ex vitro transplantation. The Journal of Horticultural Science and Biotechnology, 76(6), 739–745. https://doi.org/10.1080/14620316.2001.11511439

Carol loves to garden and research to help others grow their green thumb.

She is working towards her dream of living close to nature.

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