Tag Archives: garden mulches

Covering the ground – our free mulching options

Oh look! I made a little display board.

Mulching is what enables us to maintain our garden to the standard we want, particularly keeping the new herbaceous plantings free of invasive weeds. Being economical gardeners, we don’t ever buy mulch in but rely on the resources we have here. I laid our main options out to photograph them.

Gravel mulch

Mulching with gravel at Wisley

I have seen gravel used at the RHS Wisley Gardens, particularly in the Piet Oudolf borders and the Missouri Meadow. In its favour, it is weed-free and it makes a good seed bed in that managed meadow where seeding down is encouraged. However, it is heavy to handle, expensive and, in a situation with herbaceous plants which need digging and dividing, it is inevitable that a fair amount of it will end up in the soil even if you make efforts to scrape it to the side. I am reluctant to use it and that is a pity because we have a small mountain range of it retrieved from the capillary beds when we dismantled them. Maybe 10 cubic metres of it and that is a lot.

Granulated pine bark is a stable mulch and a neutral dark brown. I doubt that it comes cheap if you are buying it for this purpose. Not only do we have a small mountain range of gravel, we also have what is referred to here as ‘the bark slug’. When we ran the nursery, everything was potted into granulated bark and Mark decreed that the bark was not to be re-used when plants were being re-potted. His position was that the bark potting mix was one of the cheaper inputs overall (he didn’t pay the bills; I was often somewhat shocked at how much the bark bill came to each month at around $750 a truck-load) and that using fresh bark cut down on weed contamination and disease issues. All the used bark went out to the bark heap and as the heap grew, it seemed to take on a life of its own and creep out like a sand slug.

Granulated pine bark – after at least a decade and fresh, but dry

We don’t re-use the old bark as a garden mulch any longer because of the fertiliser bubbles within it. We always used Nutricote as a fertiliser for commercial plants and very good it is too. But, and it is a huge but, the coating on the fertiliser granules remains long after the actual fertiliser has been used. Mark initially rejected the use of the waste bark on paths and gardens because his eye zoomed in immediately to the fertiliser bubble casings within it. Now we are even more concerned that it does not appear to be biodegradable and we don’t want to be spreading a non-biodegradable product through the environment.

This is not a problem that you will have if you buy in bark chip because it won’t have fertiliser added (and not all fertiliser comes with a coating). To the right, is fresh(ish) bark that we still use as a potting mix. To the left is what it looks like after more than a decade in our bark heap. Despite being an organic product, pine bark does not decompose readily.

Commercial chipping at the top, our home chipper below

Next is the woodchip mulch after nearly two years on the garden. It is not my favourite mulch but we were given a large truckload of freshly mulched copper beech branches and leaves and I needed to cover a few hundred square metres of newly planted garden. Beggars can’t be choosers. It was put through a commercial mulcher and is much coarser than we get out of our domestic mulcher machine. It is very light to handle and forms a crust across the surface, discouraging weed growth. I just don’t like the colour – it is pale creamy yellow when it goes on – and because it is so coarse, it takes a long time to mellow out to something more neutral. And I don’t like the coarseness. It looks… utility, which indeed it is.

Our home-generated woodchip, being of a finer texture, discolours far more quickly and is less dominant visually. But it takes a lot of prunings to generate much quantity.

Evidence of nitrogen robbing at the top – plants are sparser and showing a yellow tinge while others have thrived

The advice with woodchip is to be careful to lay it on the top because it robs the soil of nitrogen as it decomposes if it is incorporated into the soil. Behold an example. I did the initial planting of this aster and laid mulch. I must have gone back into the area to add some more plants. Clearly, I was not sufficiently careful to scrape the mulch to one side and some of it was dug in when planting. The somewhat bare area and yellowish tinge to the plants are signs of nitrogen deficiency. I keep telling myself to get out and scatter a bit of blood and bone on the affected plants to combat this but we do not generally add fertiliser to our garden so I haven’t got around to it yet.

Leaf litter mulch

Smaller leaves look tidier

Next up is leaf litter – natural, free, nutritious, enabling a healthy soil ecosystem but untidy for small, tightly maintained areas. The birds will scratch amongst it (which is a sign of a richer soil environment because they are looking for food) and it often needs raking back into place until it builds a good under-layer. I like leaf litter mulch visually but where I am using it is in larger, more naturalistic spaces. It would not be my first choice for small, confined areas. Though the smaller your leaves, the tidier they will appear.

Compost is king

And finally compost – our preferred mulch by a country mile. Because our soils are so friable, we generally add compost as a mulch rather than digging it in around the roots of the plants. The worms will do the work and incorporate it over time. We often choose to put the woodchip and leaf litter through the composting process first. Compost is light to handle, natural in appearance and makes a major contribution to soil and plant health. We make a lot of compost here, putting it through a process that heats up sufficiently to kill off many nasties but even so, we try and avoid putting seed heads and invasive plants on the compost heaps. The problem is that even though we have compost mounds that are turned by tractor, we don’t make enough to compost to meet our mulching needs which is why we sometimes have to go to alternative options.

Our gravel mountain (with a pretty apricot foxglove seeding into it)

Upon reflection, I may have to turn to the gravel mountain to mulch the new grass garden that I plan to plant this autumn. It is about 450 square metres and laying an 8cm mulch across that area is going to take a lot of whatever I use. At least this is a planting that I do not anticipate having to do frequent digging and dividing.

Outdoor Classroom: guide to garden mulches

There are five good reasons to mulch your garden:
a) Mulches suppress weeds when laid to a depth of around 6cm (but the mulch itself needs to be free of weeds).

b) Mulches stop soils from drying out as quickly by slowing evaporation. However they should not be laid on ground which is already dry because they will act as a barrier to stop water soaking in easily when it rains.

c) Some mulches will feed the soil and add valuable carbon content.

d) Mulches protect your soil from wind, torrential rain and erosion and may slow the leaching out of goodness.

e) Most mulches make a garden look much more attractive and reduce dust.


1) Pea straw is popular but when used in areas where peas are not grown commercially, it has a heavy carbon footprint in transporting it. It should be weed free. It adds carbon content to the soil but it is a myth that it fixes nitrogen (peas store the nitrogen in their roots but you are only buying the harvested tops of the plants). It is better in the edible garden, and great for strawberries, but not very aesthetic in the ornamental garden. A bale should cover about 6 sq metres. Water it well or the dry straw may blow away. Oat straw and barley straw are suitable substitutes.

2) Composted bark is widely used and lasts a surprisingly long time. Compounds in the bark stop it rotting down quickly. It adds carbon over time, it should be free of weeds and it is visually discreet in the garden because it is dark brown. Buy pre-composted bark if you can – it does not rob the soil of nitrogen as it breaks down. You can buy small bags but it is cheaper in bulk. A cubic metre should cover about 15 square metres.

3) Leaf litter is readily available and free in autumn. You can either disperse the litter over the garden beds immediately or you can rake it into piles and let it start to decompose first. A leaf rake makes this task much easier than trying to use a garden rake. Leaf litter will enrich the soil but it may look a little untidy in some garden situations.

4) Wood chip, sawdust, and wood shavings are not composted so must be laid on top of the soil and never dug in until they have rotted. This is to avoid them depleting the soil of nitrogen as they break down. Sawdust or shavings must be from untreated timber (tanalised timber is toxic) and fresh sawdust can look garishly orange on the garden. We use the fine wood chip from our mulcher extensively, raking it out immediately to a layer of about 6cm.

5) Old carpet must be natural fibre (generally wool), not synthetic. Test it with a flame – if it melts, it has synthetic fibres. Cutting with a Stanley knife is probably the easiest way to get manageable pieces. It may be best in the vegetable garden because it is not attractive. Lay it with the hessian backing side upwards and you can camouflage with leaf litter. Similarly, newspaper is not an attractive looking option, but it will work if you lay down a thick layer of maybe ten sheets at a time. Coloured pages are fine but avoid any glossy paper. It needs to be weighted down and covered with other garden litter to keep it moist. It represses weeds and adds carbon content.

6) Compost is our preferred option by a country mile but if you are using your own compost, you need to make sure it is as free of weed seeds as possible. Compost adds most of the nutrients the soil needs and is excellent laid as a mulch on top. Let the worms gradually incorporate it into the soil. It looks unobtrusive while nourishing and protecting the soils.


7) Stones are heavy to handle but can be visually effective in the right setting. They also store warmth for plants which prefer hotter conditions. They are best used with permanent plantings where the ground will not need to be cultivated (dug over) as you do not want to have to move the stones. Use a leaf blower to keep the build up of litter removed.

8) Limestone chip can be quite a stark white when first spread but this sometimes suits modern gardens. It is weedfree but it adds nothing to the soil. Once you have laid it on the garden, you will never get rid of it. Acid loving plants like rhododendrons and camellias will turn yellow because the alkaline lime will leach out. The same goes for crushed shell, which is also alkaline. The only way to keep these mulches clean and smart is to use a leaf blower to remove detritus.

9) Fine gravel and scoria are similar options. Fine gravel is a traditional mulch for rockeries and alpine plants because it is free draining and a neutral material. It can look a little industrial or utility in other settings. Scoria will give a decidedly retro 1970s’ look.

10) Weedmat is a commercial product designed predominantly for nursery use. It suppresses weeds and allows rain to penetrate while preventing excess evaporation. It should be laid taut and secured with wire hoops. It has no aesthetic value at all and looks uniformly unattractive when used in home gardens. It is at least better than its precursor, black polythene, which should never be used as a mulch because it sours the soil. Weedmat is bought by the roll and widths vary but it should price out around $1.25 a square metre.

In the Garden this week: Friday December 24, 2010

• Dear Santa, thank you for the pre-Christmas gift of rain. But enough is enough. Water tanks are overflowing, the grass is growing again and we really could do with a return to sunshine and warmer temperatures for the Christmas and New Year break.

• Watch for an explosion of fungal ailments in the humid conditions, especially on tomatoes, cucurbits and potatoes. Roses will also suffer but they can grow out of it whereas vegetables can succumb entirely. It will almost certainly be necessary to get a copper spray on when the weather dries out. If you would rather try baking soda, a level teaspoon per litre is the recommended dose. The big problem with baking soda is that you have to spray a great deal more frequently – probably weekly.

• The wet weather means that you can still lift and divide many clumping perennials even now. Most of them are in full growth, so as long as you make sure they don’t dry out, they will recover quickly. Replant into well cultivated, tilled soil enriched with compost.

• Grapes need thinning out. We keep to one bunch per side branch. More is not better and you can over crop grapes, leading to inferior fruit. Trim back laterals. If they get too heavy, they can break away too easily and you will lose your bunches of fruit. You also want the plant to concentrate its energy on the fruit, rather than the excessive leafy growth.

• If you have not mulched your garden beds and were alarmed at the recent dry spell, this week’s rain has probably raised the moisture levels sufficiently for you to get a layer of mulch on now. We much prefer vegetative mulches which break down and get incorporated into the soil over time – compost, leaf litter, bark or shredded wood waste and the like. Inert mulches like stones, gravel or lime chip do work to keep the soil moist and suppress weed seeds to some extent but they are not suitable for gardens that you want to dig over or replant at any time and they certainly do nothing to add nutrients or texture to the soils. They are best for areas you don’t actually garden and even then, they are a bit of a mission to keep clean unless you have a handy blower vac.

• Keep up with deadheading (basically anything that has finished flowering) and try and stay on top of the weeds which will have been triggered into rapid germination and growth by the rains.

• If you had a problem with silver leaves on rhododendrons last year and haven’t sprayed this spring, check underneath the leaves for something that looks like dirty threads. These are the thrips which suck the chlorophyll out of the leaves. Photinia and honeysuckle both harbour thrips too. If you are going to spray, it needs to be a systemic insecticide so the plant sucks it into its system (as opposed to a contact one which only kills insects where it touches). Bands soaked in neem oil secured around the trunk are getting good reports. If you want to make your own, soak a strip of old woollen carpet in neem and then secure it around the main stem with the carpet pile inwards. Thrips don’t usually go away of their own accord. You either need to change the growing conditions, kill the insects or remove the host plants altogether.

Crystal ball predictions for the 2010 gardening year

Ah, that wonderful Christmas – New Year hiatus. In the days before the Boxing Day sales and indeed before seven day trading, it used to be more of a coma than a hiatus but even now, in this country, we settle in to holiday mode. Why else would we tolerate the truly appalling offerings on television where there is rarely anything worth watching? Clearly we are all meant to be reading the Christmas books or chatting to family and friends instead. And the print and electronic media, yours truly included, sink into a period of reflection, summarising the year past and bravely making predictions for the year just starting. This is at least one step better than recycling earlier offerings under the headings of “ 2009 Highlights” or “Best of…”. So I shall resist the temptation to recycle a piece from earlier this year (though I will admit to being proud of the series I wrote on English summer gardens which is still on this website) and look into my crystal ball.

I believe we will diversify from vegetables. Veg gardening is not fad or fashion but the all consuming obsession is showing signs of dilution. There is a hint that some would like to read about other types of plants and gardens as well as home food production. I recall an Auckland journo wryly commenting on the $70 lettuce. That is the cost for some of producing their first and sometimes only produce after buying planter boxes, the bagged potting mix and compost, the most basic of tools and punnets of small plants from the garden centre.

Serious vegetable gardening will continue for some, but many of those who follow fashion and trends will be realising by now that to be a successful vegetable gardener requires some expertise and skill and quite a bit of time. You can not just plant the seeds or baby plants and then ignore them. Dilettantes will lose heart and move on. The declaration that one will only plant productive trees and shrubs may be a sign of naivety and not the higher moral ground. It could be argued that the doom and gloom of the recession had us all looking to survival mode. Now that the clouds are lifting, increased optimism allows space for aesthetics and beauty in life as well. And I can assure you that while the walnut tree I see outside my window fruits and we enjoy its harvest, it is but a poor aesthetic specimen compared to the magnolia nearby which is lush and opening its summer flowers. We need to nourish more than just the body and to titillate more than the taste buds. In our eyes, the complete garden goes well beyond just fruit and vegetables, although they are an important element.

The upside of the vegetable craze has been the return to some old fashioned values of seasonal eating, taking pride in home produce and super fresh ingredients given a new twist with some rather more sophisticated international flavours. I reviewed a rather large number of cook books last year for the food pages (Second Daughter was fearfully impressed last week with my shelf of recipe books and I only keep the ones I like) and certainly the current focus is very strongly on eating locally sourced foods in season. The delight in being able to transcend seasonal limitations by buying food which has crossed the hemispheres is a thing of the recent past for many of us. We now care whether the garlic and onions come from China, the grapes and nectarines from USA, the kiwifruit from Italy and the pork from Australia. We would rather it came from Te Kuiti or the Rangitikei, thank you, if we are to move outside our local area. So I would expect we will see farmers’ markets go from strength to strength.

The local focus of the farmers’ markets may well extend to wider gardening practices. Here, we raise our eyebrows at the widespread use of mulches, potting mixes and composts shipped across the country when there are local alternatives with much smaller carbon footprints. Pea straw is the classic. It has a great reputation as garden mulch (though it is a myth that it adds nitrogen to the soil because the nitrogen is in the roots of the pea plant and pea straw by definition, is the dried tops only) but have you ever asked yourself where the nearest commercial production of peas takes place? It is being shipped hundreds of kilometres in a large truck in order to cover your garden when there are local alternatives which will do just the same. Try locally produced granulated bark or compost, pine needles, even barley straw from South Taranaki.

The move away from poisons and sprays is a trend we expect to see escalate. Our tolerance level in this country for the use of some extremely heavy duty toxins is very high indeed, often justified as a lesser of two evils. 1080 is the classic: this mass poisoning on a grand scale with a particularly unpleasant toxin which enters the food chain is government sanctioned but we are seeing the tide of public opinion turn. At least 1080 is tightly controlled, whereas the over the counter poisons that are freely and abundantly sold here are arguably worse. Rats, mice, possums and rabbits – you too can bowl into a shop and buy some nasty poisons. The trouble is that many will enter the food chain, some have no antidotes, some are appallingly slow acting and unpleasant and in this country we are all too cavalier in our use of them. Worry whenever you see the term by-kill. It is the unintended death of other life than the target. A cute little dog named Wilfred, in our case, and the poison that killed him did not originate from our property. While we shoot all our possums here, a common possum poison used by others is very slow acting and can enter the food chain. We are having to review our long held practice of feeding the carcases to our animals. The time when we see a sharp reduction in the usage and availability of such toxins can not come soon enough for us, or indeed for the environment of our country.

Buffy the cat, potential by-kill, even even though Mark shoots all our possums. Slow acting over-the counter poisons may mean the carcase is already toxic.

Buffy the cat, potential by-kill, even even though Mark shoots all our possums. Slow acting over-the counter poisons may mean the carcase is already toxic.

Organics, we predict, will become more mainstream and increasingly widely practiced. It may not be organics as the purists know it. Indeed it is highly likely to be a heavily diluted form and possibly derided by the dedicated converts. But anything which sees gardening move away from practices and habits which rely more on the use of chemicals than on good gardening strategies has to be an improvement. If we follow the European trends, ever tighter government controls will stop home gardeners having access to a range of sprays and artificial fertilisers which have been used to prop up poor gardening practices, poor plant selection or unsustainable habits.

The wheel is turning. After a decade or more of rampant consumerism, conspicuous wealth and people who are time-poor, gardening is on the up again and for that we have the vegetable craze to thank. It all looks a great deal more wholesome and cheerful than a few years ago. Happy New Year and may 2010 be one of good gardening cheer for readers.