Mulch - can it increase winter water logging?

Swooping Swallow

I've bought some mulch for a herbaceous border that's planted with drought tolerant plants. The mulch will help reduce water evaporation during summer, but is it also the case that mulch can trap excess water in the soil during the winter? Some of the plants I've planted are intolerant of excessive winter wet (e.g., Gaura, Achillea) and I wouldn't want to make that situation worse.

Hopefully it's the case that evaporation will be minimal during winter, in which case mulch won't make much difference in this regard.

Fairygirl

It would depend partly on the type of mulch, but if the plants are in a suitable medium, with good drainage, mulch should make little difference. 
A mulch of compost is probably the best solution, because it will do the job you want at this time of year, but will break down into the soil for wetter weather in autumn/winter and just help the general condition of the soil. 
In wet areas, winter rain/sleet just goes through mulch anyway. 

Pete.8

I don't think the mulch will be a problem.
I've found with Gaura (at least) that if they spend the winter with wet roots, they die.
If they're planted in soil that drains well, they're fine as Fg mentions above.
In one part of my garden where the soil is free draining they grow well and self seed.
In another part (Essex clay) they don't usually survive the winter.
I've since improved the clay area over the last few years and now they grow well there too.
I also have achillea and that grows well regardless of how well the soil drains, but it would prefer free draining soil.

Swooping Swallow

Fairygirl said:

It would depend partly on the type of mulch, but if the plants are in a suitable medium, with good drainage, mulch should make little difference. 
A mulch of compost is probably the best solution, because it will do the job you want at this time of year, but will break down into the soil for wetter weather in autumn/winter and just help the general condition of the soil. 
In wet areas, winter rain/sleet just goes through mulch anyway. 

I never understood compost mulches! Doesn't it just become 'part' of the soil, so to speak, rather than a separate barrier that can reduce evaporation. 

Swooping Swallow

Pete.8 said:

I don't think the mulch will be a problem.
I've found with Gaura (at least) that if they spend the winter with wet roots, they die.
If they're planted in soil that drains well, they're fine as Fg mentions above.
In one part of my garden where the soil is free draining they grow well and self seed.
In another part (Essex clay) they don't usually survive the winter.
I've since improved the clay area over the last few years and now they grow well there too.
I also have achillea and that grows well regardless of how well the soil drains, but it would prefer free draining soil.

It's interesting to find you've had the same issue with Gaura. I've planted a couple in the newly prepared border with their crowns a little prominent, so hopefully that will help. What you say about Achillea is promising. Fingers crossed...   

nick615

Swooping Swallow  I had to consult my ODE which gives 'Capillarity' as 'The tendency of a liquid in a capillary tube or absorbent material to rise or fall as a result of surface tension'.  To me, this explains why a bone dry lawn this afternoon becomes drenched with dew tomorrow morning, as the continual rise of water from deep down met cooler night air and condensed.  My assumption has always been that a mulch traps some of the rising water and prevents it evaporating.  Worms etc. come to the surface at night, devour rotting material and convert it to usable soil, so, while ANY mulch will have that effect, its nutritional content will govern how it affects plant growth.  Ain't Nature grand?

Loxley

Mulch is probably going to have little impact over winter, but avoid heaping it around the crowns of plants that are prone to rotting off. 

Fairygirl

Pete.8 said:

I don't think the mulch will be a problem.
I've found with Gaura (at least) that if they spend the winter with wet roots, they die.

Or they just die anyway ...which mine did 
I didn't expect it to manage, but thought it was worth a shot. Even in a good site with plenty of protection, and competition, from other plants, it was a bridge too far. The previous couple of winters might have been ok, but not this year. Back to nearer normality. 

@Swooping Swallow -   Compost mulches will gradually be incorporated, so that's why it suits any plant, but heavier mulches take longer, so that can be a problem.
As @Loxley says, keeping anything away from slightly vulnerable plant crowns is always a good idea. Things like peonies for example, where you don't want them too deep anyway, would suffer a bit. Mine are always planted quite high to counteract the soil and conditions, and ensure flowering. 

Swooping Swallow

nick615 said:

Swooping Swallow  I had to consult my ODE which gives 'Capillarity' as 'The tendency of a liquid in a capillary tube or absorbent material to rise or fall as a result of surface tension'.  To me, this explains why a bone dry lawn this afternoon becomes drenched with dew tomorrow morning, as the continual rise of water from deep down met cooler night air and condensed.  My assumption has always been that a mulch traps some of the rising water and prevents it evaporating.  Worms etc. come to the surface at night, devour rotting material and convert it to usable soil, so, while ANY mulch will have that effect, its nutritional content will govern how it affects plant growth.  Ain't Nature grand?

If I understand you correctly, a mulch will indeed prevent evaporation of water during winter months (we know it does this during summer), which is likely to be a negative impact on drought tolerant plants as they seem to do better on soil that doesn't become water logged during winter. One reason I don't want to use bark is because it takes a long time to break down and as far as I can tell, a treated straw mulch does have nutritional value for the soil and does break down over the course of 1 to 2 years.      

Swooping Swallow

Fairygirl said:

It would depend partly on the type of mulch, but if the plants are in a suitable medium, with good drainage, mulch should make little difference. 
A mulch of compost is probably the best solution, because it will do the job you want at this time of year, but will break down into the soil for wetter weather in autumn/winter and just help the general condition of the soil. 
In wet areas, winter rain/sleet just goes through mulch anyway. 

The plants are drought tolerant types (e.g., Gaura, Achillea, Perovskia, Artemisia etc). I know Gaura dislikes wet winter ground as I've lost several in the back garden over wet, mild winters. To combat this I've planted the Gaura with their crowns protruding from the soil and will put something (I don't yet know what) over the crowns to protect them from winter frosts.

I suspect the a number of the plants will die over a wet winter as I discovered a couple of days ago a large concrete pan about 18 inches beneath the surface. I had no idea this existed when I dug in manure and only noticed when I dug a deep hole for a Lavender Augustifolia (it's in a deep pot and the roots go all the way down the pot). I've no idea how extensive the pan is. Hopefully it's angled and will allow some drainage, but I suspect it will actually collect water over winter and see off the drought tolerant plants. I didn't plant the Lavender for this reason. How on earth do you find plants for soil that is dry, sandy and stony, and very dry over summer, and yet becomes water logged during winter? Perhaps this will become a common problem as climate change gives us long, dry spells in spring and summer and very wet winters.  

I'll just have to wait and see how things develop during the spring! Hopefully it'll be OK as the amount of time and effort (not to say expense - plants have become ludicrously expensive!) I've put into this is crazy...  



  

Topbird

I think that concrete 'pan' presents problems beyond winter water logging - especially if it covers a large area. It will probably be the reason the soil doesn't drain in winter and dries out so much in summer. Tree and shrub roots also won't penetrate it and you'll always be restricted to shallower rooted plants - which are often more affected by soil moisture levels.

You may need to investigate how large the pan is and perhaps give some thought to breaking it up. That would both aid drainage in winter and would also give plants access to deeper ground water in summer.

Finally, if you're resigned to living with the concrete pan, you'll find some of the hardy geraniums are more forgiving of the extremes of wet and dry. So long as it isn't sopping wet they'll cope with a bit of damp through winter and (with a deep spring mulch of organic matter on the winter-wet soil) they'll cope with a bit of summer drought.