About 40 years ago, I managed to kill half a dozen grapefruit trees. A friend was replacing her old carpet and kindly gave me the ripped-out stuff. "Perfect mulch to put around the new trees," I thought. "It will keep the weeds out and the moisture in." I duly surrounded each of my new grapefruit trees with lengths of carpet.
It worked, too. Not a single weed poked its head above that carpet for about 15 years. Sadly, though, the elderly carpet not only kept moisture in, but moisture out. The soil around those trees stayed dry except after long, heavy rainfalls when water could seep under the carpet.
There weren't many long, heavy rainfalls that year, just light falls of 3-5mm every week or so, enough to keep the other citrus happy. But my weed-free grapefruit trees turned brown after three hot days and by the time I realised what the problem was, nothing I could do revived them.
Sometimes "about-ground" veg and flower gardens can have the same problem. They can be wonderful, far easier than digging, a way to turn unwanted lawn into lettuce and tomato plants in an hour or so. They can also be a menace.
I fell for the concept of "above-ground" gardens as a child, when my grandmother took me to visit the garden of her neighbour, Esther Deans, who'd later become a heroine of the above-ground gardening fraternity. Mrs Deans kindly agreed that the lemon I adored had "just fallen off into my hand" - it was the first tree fruit I had ever picked. Her garden seemed a miracle - trees that grew food on them! It still seems a miracle, when I look at my garden today.
Esther Deans' above-ground gardening method involved putting down a thick layer of newspaper, and then at least 30cm of compost or mulch on top, preferably more. Now plant. That's it - instant garden, with no weeding. You can even place the new garden on top of your lawn, surround it with edging so the grass won't invade - you can now buy pre-fabricated edging of many kinds at the garden centre or Bunnings. Water, feed, pick, then plant again.
I used this method for several years of vegie growing. Our would-be vegie garden didn't have soil back then - it had been overused so badly commercially that it was now shale, pale yellow and almost as hard as its granite rocks. I carted tonnes of stable tailings in the green truck for years, spreading it over newspapers donated by friends, till finally we had about half an acre of truly splendid veg. No veg grew up through the newspaper, though it wasn't entirely weed free. Birds and visiting possums imported seeds in droppings or from fur. But it certainly didn't have the luxuriant weed growth of an area that had a rich supply of many kinds of weed soil dormant in the soil.
There were problems. Carrots only grew to the length of my hand, and stopped, or curved into interesting shapes. The above-ground spuds spread their tubers outwards, not downwards, so we needed to mulch them right up to their top leaves to get a decent crop. Shallow-rooted veg like lettuce did well, but even tomatoes, it seemed, found it difficult to force their roots through the newspaper barrier to the soil below. When I dug up some of the garden, half a dozen years later, the newspaper was still pretty much intact, with two kinds of soil, one above, and the shale below. The newspaper - or cardboard or, worst of all, old carpet - forms a barrier between the micro life in the soil and the stuff on top. They may take years to combine, to the detriment of both.
I gave up using newspaper in my next vegetable plot, and just piled on the stable tailings (straw, sawdust and horse manure) as mulch instead, using about twice as much mulch as I had using the newspaper. It worked beautifully.
My above-ground garden method now involves mowing weeds or grass, then mulching thickly on top. Autumn leaves or wood chips or sawdust are my favourites, as they are most easily available, but if I had my druthers - and enough money - it'd put down a thick mulch of pea straw or lucerne hay, then layer compost thickly on top of that.
Autumn leaves, wood chips or sawdust do break down into soil, but they can take years to do so - unless you sprinkle fertiliser on top. I mostly use hen manure, but other fertilisers sprinkled on top of the mulch are good too. Their extra nitrogen and phosphorus help break down the mulch; the earthworms and other soil life pull the mulch down into the soil, and you end up with an extremely good garden, with no back-breaking digging, though the hefting of mulch needs to be done with back-tending care. Keep the plants well mulched with more hay or lawn clippings, and once they are established you should never have to do any major weeding, digging or fertilising again. Regular mulching will be all it needs, plus pulling out the odd wind-blown or bird-dropped weed and giving some extra plant tucker now and then, plus watering, though the garden bed will retain moisture well once it has combined with the soil below.
Above-ground gardens are also excellent for small, temporary beds. I place small piles or a layer of soil or compost on top of a pile of weeds in the middle of a patch of grass, plant a pumpkin seedling, and water well, giving them liquid manure, hen manure or blood and bone until established (It is very hard to overfeed a pumpkin). The pumpkin vine can then spread itself all over the lawn. When the leaves have died down and the pumpkins have been harvested, rake the whole lot away and let the grass recover. This is a useful method if you are renting, and suspect your landlord would prefer a lawn to a pumpkin patch.
If you don't have any compost or good weed-free soil to put on top of the mulch, dig up a small patch of dirt with a tablespoon, then part the mulch and plant your seed or seedling in the tiny clear patch, surrounded by the hay. This works especially well for vigorous growers like corn, tomatoes, chilli, and capsicum. The grass under the hay decays quickly with the fertiliser and watering; and the heat generated by the decay speeds up the plants growing on top of it.
Part the mulch temporarily for seeds like carrots, too, though wait till the weeds and grass below have dried before you try it. I rake the hay/leaves/wood chips away, scratch away just enough soil to cover the seeds, then scatter the seeds in a low row and fluff the soil over them. No digging is needed. Plant smaller carrots life the delicious Ronde de Nice if you use this method, as carrots may fork as they try to grow in tough soil. As the mulch slowly joins the soil below, the dirt should be soft and loose enough to grow the longer carrots - though if they meet a rock you my get a two-legged carrot as the root grows either side. I plant potatoes by dropping a spud in the weeds, then add about 60cm of hay. The spud grows through the hay; the weeds die.
Most importantly: DO NOT ADD NEWSPAPER OR CARBOAD OR CARPET. All you really need is to double the amount of mulch.
The exception to this is when you have stubborn weeds like blackberry or broom or serrated tussock. Mow the weeds as low as you can, with mower or whippersnapper or tractor, and THEN cover them with cardboard or carpet - but make sure it is the kind of carpet that will eventually decay. The plant material below will die - though it may try to keep under the edges, so keep an eye on it. After three years or so the weeds below should be happily deceased. Rake away what's left of the carpet, newspaper et al, and plant grass, veg, fruit trees, flowers - whatever you and the possums desire.
This year we have been mulching with the remnants of the woodchipped fruit trees that died in the drought and fire winds of two summers ago. There's not much tucker value in the wood chips, but add some old hen manure or other fertiliser and they break down fast, and the garden grows wonderfully. Better still, the rain can penetrate them - though it is worthwhile checking that rain can penetrate any mulch you decide to put out. Lawn clippings particularly can form a rain-proof mat over the soil. They are best mixed with leaves, or other material to aerate them.
I am still mourning those grapefruit trees. But they taught me to be very careful indeed about what I mulch with, and how much.
This week I am:
- Lavishly picking and giving away the most gloriously fat crop of camellias we've ever grown, and sweeping camellia petals off the steps - they become slippery as they decay.
- Knowing I should be spraying the young cherry and peach trees at bud swell with Bordeaux fungicide to help prevent blights and leaf spots and fruit rot, but probably won't be.
- Wondering if it's safe to put the potted coffee bushes out for spring and summer yet (no, not yet).
- Hoping for the first asparagus spear of the season (yum).
- Feeding everything I can get around to just before every shower is due - never leave fertiliser on dry ground.
- Watching the early peach blossom unfold, and the crab apple buds get larger.
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