What we plant in the soil of contemplation, we shall reap in the harvest of action - Meister Eckhart
May 4, 2011 6:01 PM   Subscribe

I want to make perfect vegetable beds and seek the advice of all you edaphologists*.

I'm constructing garden beds for vegies this spring (southern hemisphere here), I know what the basics of their physical construction will be, it will be retaining walls terraced down a slope with a path in between. About a metre high on average (less uphill and more downhill obviously), 80cm wide. Three flights of 4 metres, so total SA about 10m2. Any advice on construction features would be good - should I line them internally, should I put drainage (slotted pipe) in, how about inbuilt watering, what sort of system?

The underlying soil is horrible useless clay sodosol. So for the soil, I was just going to import some basic (manufactured) garden soil from the local garden supplies place and fill the space. Working it out now it seems I'll need 10m3. Gah my back! I have about 50 kg of worm castings, and ready access to horse poo, but how else would you structure or enrich the soil? ideally I'd like to get the beds going, or at least one of them, straight away for summer tomatoes, I could fallow most of it for a while if that's important? What else could I or should I consider or do?

Not sure it's relevant but I'll be growing a wide range of vegies including brassicas through winter, it's a fairly temperate clime. Mostly annuals, a few perennials including asparagus and rhubarb. I'm not averse to the appropriate, limited use of chemicals. Oh and I'm fairly lazy in the long run - the very idea of no dig or low dig appeals to me on that level (though I don't really understand it.

(In a few months I anticipate I'll be posting an askme for your favourite vegies to plant).

* no I didn't know it was a word until just now either.
posted by wilful to Home & Garden (18 answers total) 10 users marked this as a favorite
Have you started composting?
posted by the noob at 6:08 PM on May 4, 2011

Response by poster: we have a worm farm and chooks, so the only thing that makes it into the compost bin are lawn clippings.
posted by wilful at 6:11 PM on May 4, 2011

I like to use peat moss to help break up the clay soil where I live, but it might be unavailable or prohibitively expensive in Australia. Maybe a clay breaker?
posted by exogenous at 6:39 PM on May 4, 2011

Growing daikon radishes can help break up clay soil.

As far as enriching it, we recently inoculated our garden with MycoGrow from Fungi Perfecti and are seeing really good results — things seem to shoot up noticeably from one day to the next. I don't know if it can be imported to Australia, but maybe there are sources for similar things closer to you.
posted by Lexica at 6:50 PM on May 4, 2011 [1 favorite]

Response by poster: I don't think I'll be using much if any of the underlying clay, this is more about creating new soil, though I will put down gypsum to break the clay and allow roots to penetrate into the substrate. Not many will have such deep roots though, looking at a metre deep.
posted by wilful at 6:59 PM on May 4, 2011

Build your soil thusly. Do not substitute perlite for the vermiculite, otherwise substitute whatever you have available locally for the compost and peat moss portions.

As for the size/shape of the beds themselves, if your property will permit it, I would strongly encourage the use of Square Foot (Meter?) Gardening concepts. There have been some other AskMe's on SFG that you might peruse. I've used 3 long (4' x 28') beds for 4 years now and the soil is incredible and it's very easy on water use. Here's another good resource: Garden Web Forum on SFG. I have one full bed devoted to strawberries and it is the absolute easiest thing in the world to harvest compared to traditional methods.

You also mentioned asparagus. Just tonight we harvested our first crop ever :) from our 3 year old asparagus bed. Because asparagus needs a fair amount of room and will literally last 15-20 years once established, I strongly encourage the setting aside of a devoted, stand-alone bed just for asparagus. We have one that's roughly 4' x 4' and it is clearly going to provide more than enough for our little family of 3.

Have fun!
posted by webhund at 7:26 PM on May 4, 2011

Response by poster: Indeed I think I will have fun!

Thanks for your answer, however, there's no way I can afford 3 m3 of vermiculite, while moss is unsustainably harvested (at least in Australia and New Zealand). I think that mix may work for a square foot (which just sounds like an uncomfortable way to walk to me), but simply isn't possible for the size I want.
posted by wilful at 7:46 PM on May 4, 2011

Watch this video.

He has a book, too. We inoculated our veggie patch with Mycogrow and we have salad like whoa!.

We're also going with a no-till method which doesn't disturb the mycelium layer or the good drainage. Also, letting the old roots rot in place rather than tilling them up allows them to return their carbon to the soil at a more natural pace. This, plus the activity of the mycelium building good soil and helping nutrient uptake makes a happy garden bed.

Mushrooms, baby. Gardener's best friend.

Best of luck!
posted by Pirate-Bartender-Zombie-Monkey at 8:30 PM on May 4, 2011

Thanks for your answer, however, there's no way I can afford 3 m3 of vermiculite, while moss is unsustainably harvested (at least in Australia and New Zealand). I think that mix may work for a square foot (which just sounds like an uncomfortable way to walk to me), but simply isn't possible for the size I want.

Understood, but garden soil isn't going to give you good results for veggies, you need something lighter. My local nursery has potting mix that uses coconut coir.
posted by desuetude at 10:52 PM on May 4, 2011

Best answer: Rather than standard 'garden soil', use an organic mix, which will be much lighter and more suitable for vegetables. Mulch is your friend - sugar cane mulch is great for vegetable gardens if you can get it way down there.

Whether you should line the retaining wall depends on what you are making them from - remember though, that treated timber is generally not so good, because the chemical may leach out and poison your plants - I don't think you have the problem with termites that we have further north, so untreated timber may be safe. Having said that, we grow vegetables fine in raised beds made from treated pine sleepers.

You shouldn't need to put ag pipe or anything in - just make sure water can drain through the bottom of the retaining walls and remember that it probably won't drain through the clay.

If you put in-built watering in, you need to be able to control beds/areas individually as different vegetables will need different amounts of water. You can buy the components pretty cheaply at places like Bunnings - plan the system and install at least the pipes when you first build the gardens, though to make it easier. We brought individual pipes back from each bed (of six 1200 x 3000 beds) to a central 'manifold' so each can be individually turned on or off.
posted by dg at 11:18 PM on May 4, 2011

Potatoes are a good first crop in a new gardening area.

I have no experience with soil bought in bags and wonder if it would be too lightweight to withstand heavy rain.

I've seen photos of a hillside garden created by using a flat shovel to lift a narrow strip of sod where the gardener wanted the upper edge of the bed. He didn't cut it off, just left that strip of sod attached and rolled it downhill. Then he lifted the next strip, rolled it over a little farther, and by the time he'd lifted the sod the full width of the bed, he had a sod roll making a raised edge along the downhill side.

John Jeavons is an expert on raised beds and biointensive planting. His method of first-time bed preparation is fairly easy on the back. After that first time, preparing the bed for planting is really easy, just swirling the soil with a garden fork. I would trust his recommendations on soil-building.
posted by sevenstars at 5:17 AM on May 5, 2011


I will sell you gopher and deer insurance for a slab a year.
posted by pompomtom at 5:45 AM on May 5, 2011 [1 favorite]

Best answer: I think people are making this too complicated. You don't need specifics in the soil, other than good soil (that is, top soil or garden soil, rather than fill dirt), with plenty of organic matter added to it. The organic matter will make it lighter and help to prevent it from compacting, but so will your set up, which makes it sound like you won't be walking on your beds.

It would be worthwhile to add something that takes up space but does not break down too quickly to your soil mix. I like coir, but have also used shredded leaves with good results. By all means add the manure and the worm castings. The worm castings can go right into beds that will be used immediately, but if the manure is not already composted it should only be added to beds a couple of months prior to planting. Any sooner and you risk burning your plants.

Compost, worm castings, manure, shredded leaves, coir...these are all the constituents of good soil. They increase tilth, and contribute to good soil structure. The process of building that structure takes time, not just because the physical additives take time to incorporate, but also because the flora and fauna that you want to cultivate (in the soil, not your crops) take time to get going. There is no reason not to plant this year (keeping in mind the manure caveat above), but there is also no replacement for caring for your soil and watching it develop and improve. In other words, part of gardening is growing your soil.
posted by OmieWise at 5:59 AM on May 5, 2011 [1 favorite]

I have a kind of meta-question: if you're dubious about this, could you only start part of your proposed garden this year, and evaluate the results tthis fall before expanding next spring?
posted by wenestvedt at 6:38 AM on May 5, 2011

You absolutely need to invest in good soil. Consider it a long term investment. Coir/Vermiculite/compost in equal parts will get you veggies for a long time. Then you just need to add compost every year or so to readd the nutrients/organic matter to the soil. It's worth it. Seriously.
posted by Sophie1 at 6:51 AM on May 5, 2011

Best answer: I'm with OmieWise on the soil thing. I've been a professional gardener for years and have studied soil science. There's nothing wrong with loamy topsoil- it's the most productive agricultural soil in the world, so don't go nuts with soil-less mixes of compost, peat, and vermiculite. You'll have nothing left in a season or two, because that's not real soil- just organic material. (Fine if you have unlimited funds and time for replacing it when it decomposes.) Amend with good compost, coconut coir, composted grape pomace, if that's available. Coir is superior to peat for water retention, but sometimes it's been processed with seawater, so consult your source, and/or rinse it carefully.

You're also going to want to do some calculations for gypsum application, so you're not wasting time or money.
nearly twice as deep than they need to be, but maybe that is due to your slope? 1.5 - 2 feet is a good average- when I design raised beds, I like them to be a comfortable sitting height since that makes it easy to work, if you put a flat board on top. A meter's fine if you have a comfortable reaching-in-while-standing depth to the beds, and you're fine with moving an insane amount of soil.
In any case, you should not need to line them- unless you have a pest problem that requires a physical barrier. If you have any inkling this might be a possibility, take care of it now. If they're on a slope and/or raised, beds don't need additional drainage, so don't worry about that. The only issue might be if all your upper beds make your bottom beds too soggy, but I would try to take advantage of that water by planting thirstier veggies in the bottom bed, if that's the case.

Irrigation- in my view, the best way to water vegetables is by hand, overhead, early in the morning. If that's more than you care to do, individual hose bibs at each bed with a battery operated timer gives you a huge amount of flexibility. This helps fine tune in case of wetter lower beds/dryer upper beds. If you need to be extremely water conscious, install drip irrigation, with a spare bib for occasional overhead watering to blast off bugs and dirt and spores (early in the morning). Otherwise soaker hose is easy and perfectly fine. Mulch with compost or straw (do not dig in the straw, re-use/compost it in a high nitrogen compost pile afterwards) to retain moisture and moderate soil temperatures. Do not add cardboard or paper products to your beds.

You can read about green manures for your winter/fallow beds. They are an excellent way to provide for nitrogen and good soil structure.

Double digging- no need to do this if the soil you buy has good texture. The natural way for soil to be built is by organic material on the surface being decomposed and worked in by soil organisms. Not much point in trying to get organic material below the top 8 inces anyway, as all the action is in soil with oxygen. If your soil seems heavy, dig in some organic material. Mulch with compost and straw on top. At the end of that season, remove straw, remove old plants (just cut off the top and leave the roots when possible), sow new ones, add a layer of compost/manure, replace straw. Or with green manures, chop off tops, compost them or chop them up, add back into soil.

You will need to weed, but you can also jam in more vegetables than most people do traditionally, in the vein of square foot gardening. This will help keep weeds down as well. It also helps to grow flowering plants for pollinators. Most companion planting "information" is bunk- look for .edu sites or whatever the agricultural extension (do they have those where you live?) equivalent is for science-based gardening info.
posted by oneirodynia at 4:28 PM on May 5, 2011

Oops, sliced off a sentence in the second para.: "Your beds seem nearly twice as deep as they need to be"
posted by oneirodynia at 4:30 PM on May 5, 2011

Response by poster: oneirodynia, the beds are indeed that size to terrace the slope properly, rather than for the sake of the plants. I think I'll look into bulk purchase of coir.
posted by wilful at 9:22 PM on May 5, 2011

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