How to mulch herbaceous perennials

Hi all,

This year was my first for putting in herbaceous perennials and I have recently added composted bark as a mulch in some areas. I know with woody plants you you don't mulch up to the stem to avoid rotting. What's the situation for herbaceous plants? Examples being lupins, echinecea, coreopsis.. I have now cut these all back but it has left some green stumps around and I don't know whether to cover them or not? And whether to note where they are and uncover them in spring? First world problem I know.. Thanks for the advice.

 

I mulch perennials with compost, bought or homemade. I put a thin layer of mulch over the plants and a thicker layer around them. I put a thicker layer over plants that need protection from frost, such as dahlias which I leave in the ground.

 

Hello @Mattyp, you don’t say whereabouts you live which makes a difference to the advice re herbaceous perennials and also which ones you are growing. I live in Scotland which is not renowned for being the warmest part of the UK!
I grow maybe in the region of about 75 different herbaceous perennials and don’t mulch/ protect any of them. Most herbaceous are better not given enriched soil as they can grow too well and fall over. Certainly Lupins grow best in totally rubbish soil, hence why you see them growing well at the side of roads! They don’t do well in rich soil, only really requiring soil that does not get waterlogged. My best advice would be to research the herbaceous perennials you have to find out if they are really hardy. The 3 you mention are and need no protection although one or two varieties of coreopsis don’t cope with really cold temperatures.
Certainly as Busy- Lizzie says the likes of Dahlias are not hardy, I have to lift and replant as too cold to leave in the ground, they, in milder parts will need a thick mulch.

 

I didn't say where I am either, though if you are using a computer I think it shows. I'm on my phone this morning. I'm in South Norfolk on sandy soil and I also have a garden at my house in SW France, a lot warmer than Scotland!

 

I don't protect anything as such either, as I only grow hardy perennials in the ground that I know will cope here.
I add compost from spent annuals to keep improving the soil in various areas, but I'd never cover the crowns of any perennials as that leads to rotting due to winter wet here. Peonies are a good example. I would just spread that in between, and it's often easier to do that before they've died back fully, so that it's easier to see them. If you're mulching anywhere as a protection, remember to do it when the ground's not frozen. If you're in a drier area, it might be ok to cover crowns of plants.
It will largely depend on what you're growing and your general climate. Dahlias have to be lifted here - I couldn't leave those in the ground. Anything that's not reliably hardy would have winter protection, and if I grow those, they're usually potted to make it easier, like the aforementioned dahlias. Most of the non hardy plants I grow are annuals, and grown each year from seed.

 

Hi all, thanks for the tips. Sounds like then I should not cover over the plants but around if anything which is what I thought. I'm in central Scotland, so cold and wet is the norm. The lupins I have are growing in clay soil and did really well this year so maybe they're just not too fussy. The bark mulch I put down really because I thought it looks nicer than bare soil and weeds that might be growing rather than any thermal properties but sure it can help with that too. I still have a few pots of used compost actually which I wasn't really sure what to do with but I guess it should be mixed into the soil or mixed with new compost for pots next year..

 

I don't really like bark around perennials, if it's the heavier rougher kind, as it tends to sit there staying wet long term. Old compost, or leaf mould is better IMO. I only use it around woody shrubs/trees, or at the foot of hedging. It's certainly good aesthetically though.

No need to mix your old compost withsoil if you use it to mulch. Just lay it on top.

 

Bark dries quite quickly here as I've got free draining sandy soil. I use it on my main grass and perennial border to keep weeds at bay. Last autumn I relocated the bark and replaced it with a bought compost mix. In spring, I found that weeds enjoyed the compost too, so I covered it with the bark again! A layer of compost and a thick layer of bark on top makes maintenance easier here.

The bark provides protection for roots in winter, retains moisture in summer and reduces the need for weeding and watering. It also makes it easier to work on the border without compacting the soil and treading mud onto nearby paving! You do need to top it up every year though.

I've also found that too much rich compost causes some perennials to fall over, producing more leafy growth than flowers. Some grasses also become less resilient to wind and rain damage, with flower stalks snapping or being flattened. They grow better in poor, impoverished soil.

 

I had wondered whether compost as a mulch still allows weeds to grow, so from an aesthetic perspective it's no better than bare soil and my main aim with the bark was to reduce weeding in one larger border made up of woody shrubs mostly. I had some left over so this is why a part of a herbaceous perennial bed got covered too.. it does help suppress weeds but you need a lot more than you think to stop them, to the point where you need to dig your border deeper to achieve the required depth which I'm not about to do.. That's a fair point about it potentially creating a wetter enviroment for longer, I guess that could be the case which can be good or bad depending on soil type and where you are. Not sure I need to hold on to more moisture!

 

It really depends on your soil type and climate @Mattyp. There’s often a compromise with most gardening practices! You may find that bark also encourages slugs and other nasties in cold wet soil, so perhaps compost and some possible extra weeding is the way to go.

 

Having a garden of over an acre and surrounded by farmland with weed infested verges I use bark and teram in places otherwise my whole life would be spent weeding. That will be a no! I only use the forgoing on shrub beds not on the herbaceous borders as if……accent on the if! you can get the borders pretty weed free early in the season, herbaceous plants will then grow up and cover bare soil. Just remember Mother Nature does not “ do “ bare soil and will swiftly take the opportunity to infect any bare areas with weed. If you scatter the old compost I think that would probably make an ideal seed bed for weeds to grow!
As @Plantminded rightly says, gardening is often a compromise. If I won the lottery I would have a band of gardeners employed to weed my garden constantly and do away with the teram and bark chip, I can dream

 

Oh great, slugs like bark do they.. I did wonder in the spring if I would regret the bark as at least on bare soil I can spot them coming whereas theyre a nightmare to spot on bark. Yeah I guess the answer is don't have bare soil but that restricts you to non-herbacoeus perennials. It is our choice how much hassle we want I suppose.

 

If it's weed suppression you are after there is one commercial product recommended by garden Which. It's mineralised straw, it's also said to deter slugs and snails because of the iron content. Some garden centres sell it, but cheaper and bigger bags available direct. Quite expensive overall but lasts about 2 years, before it breaks down into the soil. So if you have to buy mulch or compost to mulch with, worth considering. Goes under the brand name Strulch.

 

Hmm interesting, might have to try that, thanks!

 

The best solution is to have as little bare soil as possible. Lots of ground cover. I do hardly any weeding.
There's always going to be weeds coming in, regardless of what you use, but I never put anything 'weedy' in my compost bin, epsecially as it doesn't get hot at any point.
Bark is certainly a slug magnet here as the conditions suit them so well, but they're present no matter what you do.