Is mulch from Leatherleaf Viburnum (Viburnum rhytidophyllum) growth-inhibiting?

[Pypes]

I have a large Viburnum rhytidophyllum in my garden, I suspect it is Viburnum rhytidophyllum 'Roseum'. Few years ago I drastically cut it down to 1 meter, shredded the material and mulched a couple of square meters. My impression was that growth of all kinds of plants and weeds may have been inhibited by the mulch for one or two years. Is this possible?

I realized that some rose nurseries advise against wood chip mulching of roses, at least against fresh wood chips because of the tannins concentrated in the bark of many trees. Oak, walnut, ash, birch, eucalyptus, willow, and pine contain high levels of tannin. But the wood itself would also contain tannin. The tannin, which has antioxidant, antibacterial and antiviral effects, influences the metabolism of the roots and their beneficial fungi. But does Leatherleaf Viburnum contain high levels of tannin? It protects itself against pests and wildlife browsing by being 'hairy', i.e. occupied with stellate (star-shaped) non-glandular trichomes, which cause allergic reactions on the skin of offenders. As this is the plant's weapon I would be surprised it would also defend itself through high levels of tannin. But is there something else contained as makes mulch from Leatherleaf Viburnum bad?

The Leatherleaf Viburnum mulch rots very slowly and keeps its structure allowing oxygen to freely get to the soil and roots. So from that perspective it could be a good mulching material.

 

[Nasir]

It is possible that the mulch from your Viburnum rhytidophyllum inhibited growth of other plants and weeds for a year or two. This could be due to several reasons, including the presence of allelopathic compounds in the mulch. Allelopathy is the ability of certain plants to release chemicals that inhibit the growth of other plants. While it is not clear whether Leatherleaf Viburnum contains high levels of tannins, it is possible that other allelopathic compounds in the plant could be responsible for the observed effect.

In general, mulching with fresh wood chips is not recommended for roses because the decomposition of the chips can deplete nitrogen in the soil, and the tannins can also be toxic to plants. However, using well-rotted mulch, such as your Leatherleaf Viburnum mulch, should not pose a problem for most plants.

The slow decomposition rate of the Leatherleaf Viburnum mulch, as well as its ability to allow oxygen to reach the soil, are both positive attributes of this mulch. It is possible that the slow decomposition rate is due to the presence of lignin, a compound found in woody plant material that is resistant to decay. While this can be beneficial in some cases, it may also mean that the mulch takes longer to release nutrients into the soil. If you are concerned about nutrient availability, you may want to consider adding a nitrogen-rich fertilizer to the soil before mulching.

 

[Pypes]

It is possible that the mulch from your Viburnum rhytidophyllum inhibited growth of other plants and weeds for a year or two. This could be due to several reasons, including the presence of allelopathic compounds in the mulch.

Thanks Nasir!!!

That keyword "allelopathic" helped me find some scientific results - your help is very much appreciated!

Allelopathic effects of Viburnum nervosum on seed germination and seedling growth of Abies pindrow Spach by Ombir Singh and Vidya Rattan documents growth inhibiting effects of Viburnum nervosum on a competitor plant. This Viburnum is not my Viburnum rhytidophyllum, but it is the same genus Viburnum, and also looking up pictures, Viburnum nervosum does not look all too different. So I bet there is some likelihood that Viburnum rhytidophyllum shares an allelopathic weapon with Viburnum nervosum. The published work documents negative effects of foliage leachates of Viburnum nervosum on seedlings of Abies pindrow. Abies pindrow is not what I am growing in my garden, but I see some likelihood that if there is impact on that species there is also impact on other species, genera and even families. The Viburnum nervosum leachate "inhibited seed germination, radicle and plumule growth, seedling height and seedling basal diameter of the receptor species".

So, I will definitely not mulch my roses with Viburnum rhytidophyllum leaves.

 

[Nasir]

Thanks Nasir!!!

That keyword "allelopathic" helped me find some scientific results - your help is very much appreciated!

Allelopathic effects of Viburnum nervosum on seed germination and seedling growth of Abies pindrow Spach by Ombir Singh and Vidya Rattan documents growth inhibiting effects of Viburnum nervosum on a competitor plant. This Viburnum is not my Viburnum rhytidophyllum, but it is the same genus Viburnum, and also looking up pictures, Viburnum nervosum does not look all too different. So I bet there is some likelihood that Viburnum rhytidophyllum shares an allelopathic weapon with Viburnum nervosum. The published work documents negative effects of foliage leachates of Viburnum nervosum on seedlings of Abies pindrow. Abies pindrow is not what I am growing in my garden, but I see some likelihood that if there is impact on that species there is also impact on other species, genera and even families. The Viburnum nervosum leachate "inhibited seed germination, radicle and plumule growth, seedling height and seedling basal diameter of the receptor species".

So, I will definitely not mulch my roses with Viburnum rhytidophyllum leaves.

You are welcome