Wednesday, 18 March 2015

How to grow your own mulch?

Growing my own mulch has long been a goal of mine. We use a lot of mulch in the nursery and garden and at the moment we have no problem sourcing straw but if/when the day comes that the farmers start using their own straw to improve their soil (which is becoming a more common practice), We'll be needing to step up our mulch growing efforts.

Currently, we grow enough mulch to sustain the perennial beds and around 10 % of the annual beds but rely on imported straw for mulching the other 90% of annual vegetable and nursery beds.

During this post we'll look at what makes a good mulch, a range of plants that we use for mulch and some possibilities for growing mulch for broad scale use.

Mulch Growing in the Garden 

What makes a good mulch plant ? 

My ideal mulch plant grows fast, is drought tolerant, competes minimally with crop plants, does not contain seed that easily spreads, is easy to handle and cut, i.e,  not thorny/prickly or tough and fibrous, and can biodegrade relatively quickly (thereby returning the nutrients back to soil).

I've broadly categorized the main sources of mulch we produce in our 1500 m2 garden and 2500 m2 market garden.

Aquatic Plants 

We grow emergent wetland species such us cattails (Typha spp), sedges (Carex spp. ) and rushes (Juncus spp.) on the banks of a small pond (6m x 3m), and within a grey water reed bed (1m x 6m). The pond also provides suitable habitat for hornworts - Ceratophyllum spp. a submerged rootless perennial that gathers on the surface en masse. This plant makes an excellent mulch being rich in nitrogen, growing very fast and is easy to position around the base of plants. The emergent species provide a good thick carbon rich mulch that helps to reduce evaporation on the terrestrial beds and we cut these back in the spring in case they are used for overwintering invertebrates. Aquatic plants are an excellent source of mulch as there are no issues with seed germinating amongst your land based crops.

The wildlife pond, aka 'the mulch machine'  

Tap rooted Perennial/ Biennials

Deep rooted perennial plants tend to produce a good amount of biomass, are generally drought tolerant and do not compete strongly with our crop plants. I have found native biennial weeds such as greater burdock - Arctium lappa a very useful mulch plant with the gigantic leaves growing back very fast after a cut. Lesser burdock - Arctium minus is also useful albeit to lesser extent :) Although biennial, if you cut back these plants before flowering you can prolong their life, harvesting good quantities of seed free biomass. It's good to allow some of the plants to flower as they are much loved by bees among other insects.

Comfrey- Symphytum x uplandicum 'Bocking 14' is a classic example of a deep rooted mulch plant. We have the plant scattered  throughout the garden and planted in dedicated mulch production patches. The plants do require irrigation however and will only provide good leaf yields if grown on fertile soil. For more on comfrey check out our blog article here. We are also using comfrey in an experimental perennial polyculture  we call the biomass belt ,dedicated to growing mulch see here more on this.   

A Perennial Polyculture dedicated to growing Mulch. - The Biomass Belt   

Helianthus tuberosus - Jerusalem Artichoke  provide a great source of biomass. For a good tuber harvest its best to wait until the end of the season before harvesting the mulch. We can never consume as much as we produce of these tubers in the kitchen but have found them to be much appreciated by our pigs and an excellent source of fresh winter food for our rabbits.

 Leaves of Greater Burdock - Arctium lappa 

Nitrogen Fixing Trees and Shrubs 

These plants take a while to establish but make an excellent contribution. I've had good results from coppicing Paulownia tomentosa - Empress Tree  when they are 3 yrs old and chop and dropping the soft new growth 3 or 4 times a year.  I am expecting to also see good results from  Alnus incana - Grey Alder and Alnus cordata - Italian Alder.  I avoid using thorny nitrogen fixing trees and shrubs for this purpose. Annual trimming of shrubs such as  Elaeagnus umbellata - Autumn Olive and Cytisus scoparius - Broom also provides good quantities of mulch.

Lawn and Ground Cover 

One of my favourite sources of mulch is lawn trimmings. They are great for mulching potted plants or applying a mulch into tight spots.  Mixed species lawns will contain a more diverse mix of mineral nutrients, and lawns including a legume such as Trifolim repens - White Clover can provide a nitrogen rich mulch. It's a good idea to leave some of the trimmings behind to keep the lawn healthy.  

Bellis perennis, Trifolium pratense, Taraxadum officinale amongst others in our lawn 

Autumn Leaf Fall and Herbaceous Stem Residue. 

The annual shedding of leaves from trees and shrubs in our garden make a great contribution to our mulch capital. Leaves can be cleared from paths,  lawns and wildflower beds (as they will disrupt the growth in these areas) and concentrated where they are of benefit such as the base of high demanding fruiting shrubs such as Blackcurrants or Blackberries.

Herbaceous perennials such as Mellisa officinalis - Lemon Balm  and  Mentha spp.- Mints will provide dead stems annually. It's always a good idea to leave hollow stems of some herbaceous perennials to remain for the winter as they are utilized by invertebrates for egg laying and hibernating. If the plant does not have a hollow stem it can be cut back and used for mulch. Foeniculm vulgare - Fennel provides large quantities of biomass and as far as I can tell the stems are not utilised by any organism over the winter.
In the vegetable garden all the remnants of my crops after harvesting go straight back to the surface for recycling.

Foeniculum vulgare and other herbaceous perennials

Tree Prunings

Woody prunings from shrubs, trees and vines cut into small pieces (5-10cm) make good mulch in the mature areas of the forest garden with well established  fungal soils specializing  in breaking down the lignified woody material.

Living Mulches 

In the more mature areas of the garden where the trees have established (5 yrs and older) I have dispensed with mulch all together in favour of ground cover plants that can be considered living mulches. Some the most successful perennial living mulches I have found that form good dense cover in the shade include  Ajuga reptans - Bugle,  Lamium maculatum - Spotted Dead Nettle,  Sedem spurium - Caucasian Stonecrop , Vinca major -Perwinkle  and  Stachys officinalis - Betony.

Lamium maculatum spreading well under a Morus alba -  Mullbery 

C4 and other Grasses 

Another great option for mulch production is perennial grasses that produce large amounts of biomass, can grow on poor to average soils are drought tolerant, reproduce via rhizomatous growth and have seed ripening from late June on wards or have sterile seed. C4 grasses are even more suitable - For more on C4 plants see here

Two plants that appear most suitable are Miscanthus x giganteus (C4) and Arundo donax (C3). In an experiment you can find here recorded yields of biomass were 40 t/ha/yr in M.giganteus and 30 t/ha/yr in A.donax. 

We are offering  Miscanthus x giganteus plants from our nursery stock see here for our plant profile 
 and have started growing it this year. 

Scaling up Mulch Production 

In order to grow enough mulch to provide a water retaining, weed excluding barrier for my annual and nursery beds I would certainly need more space. A larger wetland area would be ideal, with aquatic species growing very fast and the seed bearing parts of the plants being non problematic to use on terrestrial beds. If you don't have a reliable aquatic habitat, the next best option for growing quantities of mulch without irrigation and fertilization is probably grass.

Check here where I share a plan to grow enough  mulch to support approx 670 fruit trees and 1360 soft fruit shrubs on a 5ha Agroforestry Project.

Alley Cropping Site Design 
If you have a favourite mulch plant, let us know in the comment box below and if you have found this post informative please share.

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  1. Vetiver grass: hard to beat.

  2. How about azolla? It grows fast and it only needs about 5 to 10 cm of water to grow on.

  3. Azolla looks great, are you aware of any species that are suitable for temperate climate US hardiness zone 5-6?

    Vetiver grass looks fantastic, not for our climate unfortunately.


  4. Hi, Paul, Victoria is supposedly zone 6. Last winter a week or so below minus 4 killed all my azolla but this year was mild winter, just a few days when it froze the azolla pond and it is coming through just fine. It is growing like mad in my greenhouse right now and outside it is alive but not exactly going crazy. Goldfish much prefer duckweed to azolla. Azolla evaporates more water, duckweed is on a par with it if it gets enough nutrients, also, azolla is I believe used in some cooking somewhere in india. (for human food.) I am going to try azolla as "moss" for hanging baskets this year. Brian.

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  6. Hi Adam

    Thanks for your compliments. I'm gald to hear you enjoyed it :)

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