So what’s your problem? (and do you even have one?)

I’ve been using Melcourt Sylvagrow for a good few years. I was using it as a professional grower for several years before I retired in 2014 and I’ve been using it at home, pretty much to the exclusion of anything else, ever since. It’s a peat free growing medium based on composted wood waste and bark, with the addition of a small amount of coir. The retail product has a low level of short term feed in it and for most purposes I add Osmocote controlled release fertilizer immediately before using it.

Before I switched to using Sylvagrow I was using peat. Peat is a unique material and has properties that make it a very good material in which to grow plants. It is effectively sterile, effectively inert and it has an exceptional ability to hold high volumes of water while still keeping lots of spaces filled with air.

A large number of materials are used in peat free composts and I only have experience with a few. Often, as with Sylvagrow, the ingredients have been composted in bulk, attaining the sort of temperatures that will kill the majority of weed seeds and pathogens, be they fungal, bacterial or whatever. It will not kill everything, it is a pasteurisation process not a complete sterilization. The ingredients will heat up like this because of the action of bacteria utilising those ingredients as an energy source, essentially feeding on it. Peat, having lain in anaerobic conditions for thousands of years, no longer contains anything that bacteria or fungi can make a ready meal out of, and is highly resistant to breakdown.

Wood and bark are a different matter altogether. Woody material, as anyone who has ever put wood in contact with soil will know, is attacked by fungi and broken down quite quickly unless it is impregnated with effective chemical preservatives. The fungi responsible are ubiquitous; even if a wood based growing medium started out sterile, it would pick up saprophytic fungi from the environment very quickly.

Today I repotted two small Camellia plants. I removed all the compost I possibly could from their roots and put them back into the same sized pots with fresh compost. The reason, the compost they were in was shot through with saprophytic fungus.

The plant is Camellia ‘Annette Carol’, from a cutting taken in July 2018. It is in a 9cm pot and the growing medium is likely to be 50:50 Sylvagrow and Peat. Just to the left of the stem base is a whitish fungal growth.

The bottom of the pot shows fungal mycelium visible through most of the drainage holes but also healthy roots emerging from them as well.

Taken out of the pot, the fungus is very prominent in the top layer of the compost and not at all evident lower down. The fungus smells mushroomy. What is evident is a curled up millipede and just to the right of it a tiny vine weevil grub.
Camellias have a strong tendency to send their roots down so if the base of the cutting is a couple of cms below the surface it may explain the lack of root above that point. Equally it may be that the pot has been topped up with fresh compost early this year. The white roots are new this year, the slightly darker roots are last year’s that have come through a winter.

Zooming in on the two critters, there is a young and small millipede curled up. I don’t know what species this is but it seems to have become very common in my garden only in the last few years. The adults are black and about 4cm long. Most millipedes are detritivores but some eat fungi and others suck sap. They don’t appear to do any serious damage but I do wonder about that when I find them in pots of cuttings or seeds/seedlings.
The vine weevil grub is no more than 3mm long and the orange granular material to its left is its frass. They are hugely destructive, especially when they ring bark plants just below the soil line. I lost several young camellias to them last year, in spite of a nematode treatment. I treated them all with nematodes today and plan to repeat the treatment in around six weeks time.

Here I have broken away some of the compost at the edge of the rootball. It appears that the fungal mycelium is present in about 50% of the compost material and it may be that it has colonised the wood and bark fragments but not the peat, though this is far from clear. The two large balls are granules of controlled release fertilizer (not slug eggs or vine weevil eggs, both of which I’ve heard them accused of being). The tiny white balls are associated with the fungus and may be a dispersal mechanism. The fungus appears to exude droplets of fluid which are the same size as these blobs, so perhaps fungus grows on them. They are hard, with a furry surface layer, and appear to be produced on the compost surface and around the rootball sides, from where they could easily be displaced to start an infection elsewhere.

In another pot I broke up last week the fungus was uniform throughout the compost but in that case it had definitely not been mixed with peat. Here though, the lighter coloured wood fragments are infected, the dark material is probably mostly peat.

The washed root system shows mostly healthy roots but also some dead amongst them. The cutting didn’t root well; it produced a lump of callus at the base of the stem and roots only emerged at one point on the left hand side in the picture.
I don’t think the dead roots are anything to do with the fungus, more likely due to drying out, weevil damage or frost damage.

This is the other plant, Camellia ‘Scentuous’, with its roots washed clean. They are in better condition than ‘Annette Carol’ and have emerged all around the cutting making for a better anchored plant. Both plants should have been potted on at the beginning of this year and when they are potted on next year need root pruning to get the root system spreading out properly.
There is no indication of the fungus doing the roots any damage nor of there being any mycorrhizal relationship between fungus and roots.

The two plants repotted into fresh compost, again a 50:50 Sylvagrow:peat mix. Great care was taken to shake and tap the compost back into close contact with the roots.
The notching around the leaf edges on ‘Scentuous’ on the right are almost certainly adult vine weevil damage.

A week ago I turned out a five litre pot containing a pelargonium which was infected with what looked like the same fungus. It was 100% Sylvagrow and the fungus was uniformly spread throughout the root ball. I broke it up, removed all the pelargonium roots and used it to pot this small collection of plants.
I then potted a duplicate set of the same plants in fresh compost.
One of the characteristics of the fungus infected compost is that it can be very repellent to water. I think the pale colour of the surface is partly due to the white fungal mycelium making the compost particles appear lighter, partly because they are resistant to absorbing water.

The left hand pot pot is in the fungus affected compost, the right hand pot has fresh compost. I must water, drain and weigh these pots to see if there is a difference in water holding capacity between them.

I have occasionally seen mycorrhizal fungi growing in pots with peat compost, mostly on conifers or birch. On the peat free composts I have seen a wider range, sometimes mycelium, as here, sometimes toadstools on the surface. I have opened bags to find fungal mycelium growing extensively in the unopened bag. Except for making the compost very hard to wet, it appears to be unsightly but harmless. If a few pots in a batch are affected and need far more water than the rest but don’t get it, there may be a problem. Otherwise it seems to be a small price attached to not using peat as a growing medium.

5 thoughts on “So what’s your problem? (and do you even have one?)

    1. I would have gone to the Exeter Grow Show which was scheduled for October and had a chat with Catherine Dawson about it. She’s their technical director and is very knowledgeable. Sadly the show has been cancelled for this year. Maybe next year. I suspect that if I contact the company I’ll get a stock reply about it being normal and inconsequential to have saprophytic fungi in growing media. In fact they flag up the possibility on their product information sheet online.

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  1. That was a very interesting read. I have come across something like this before in some of my self-potted pots, and also noticed that it does seem to make the potting mix more hydrophobic. I will be more observant next time I notice fungal mycelia in my potted plants. I tend to mix a couple of products to create a better potting mix. Most of the ones you can buy here are bark based and often too porous. That was also interesting info on the vine weevil grub.

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