Growing in a raised bed can help you grow on the toughest of ground but from time to time you will need to reinvigorate the soil to keep your garden growing. Read on to find out how to make your raised bed soil rock.
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Soil is amazing stuff. The natural cycles in the soil create the nutrients needed for plants from the decay of organic matter.
The beautiful gardens of Cawdor Castle, Scotland.
The soil plays an important role in both the hydrological or water cycle and the carbon cycle on earth.
The largest reservoir of carbon globally is in the earth’s crust in the rocks and sediments. From a living organism perspective, carbon is present in humus which is derived from protoplasmic constituents of microorganisms and plant matter which has resisted decomposition.
Photosynthetically fixed carbon in plant matter is eventually broken down by microorganisms into methane and carbon dioxide as part of the redox cycle. They are generated by methanogens and chemoorganotrophs through fermentation and aerobic and anaerobic respiration.
Uncompacted soil grows great plants, provides an ideal home for many soil microbes and fungi as well as soil insects and critters such as worms.
The ideal soil is made up of approximately:
- 25% air (pore space)
- 25% water
- 45% mineral fraction (ground rocks and particulates which are inorganic)
- 5 % organic matter.
Soil may be altered by incorporating organic material, mulch and the addition of inorganic, mineral components.
The Best Raised Bed Soil
Raised beds need soil which will provide the nutrients and water needed by your plants without them becoming waterlogged. Raised beds can also lose water really quickly meaning that your plants dry out a lot faster this can happen with taller raised beds or in dry climates like Utah.
When filling a raised bed, I use I mixture of:
- organic materials such as leaves or grass clippings
- manure, 1 shovelful, scattered in
- worm castings, 2-3 handfuls scattered in
- rockdust, 1-2 handfuls dusted in
- kelp meal, 1-2 handfuls dusted in
- organic raised bed soil with perlite or vermiculite added.
- coconut coir
The compost, raised bed garden soil, coconut coir and organic materials change depending on what is available or how much the raised bed as decreased in volume.
Understanding your climate will help you choose materials needed for your raised bed soil. For example, adding more humus helps my soil keep moisture but a gardener in a wet region would want to add perlite or vermiculite to aid with drainage.
If you don’t want to use purchased, bagged raised bed soil then use this mix modified from Mel Bartholomew’s Square Foot Gardening Mix: 1/3 coconut coir, 1/3 compost and 1/3 coarse horticultural grade vermiculite. I try to avoid peat at all costs since it is a delicate natural resource, coconut coir makes a great substitute.
If you are a regular reader, you know I’m a little crazy about composting and I try to produce as much of it as I can. One of the big reasons for making compost is to build my raised beds without needing to purchase it. A good organic (or biodynamic) compost can provide your garden with all the nutrients it needs each season. You can read more about composting here.
Building Your Raised Bed Soil
I have used organic bagged soil from big box stores, sheet mulching, compost and even hugelkultur in my raised beds and I’m going to share with you what has worked the best for me here in Utah.
- If you are setting up a new raised bed, put cardboard down first to smother weeds. If you follow me on YouTube you may have seen my garden tour videos and my bindweed woes. Start your raised beds right and cover the weeds and grass with cardboard. Worms love cardboard too so it will encourage more to your garden beds as well!
- Add some leaves, grass clippings and leaf mold.
- Add raised bed soil or raised bed soil mix and mix in a shovel-full of well rotted manure. I have some manure from a local horse owner or I use composted chicken coop bedding. Manure should be aged or composted for at least 6 months before use. Find out more about gardening with manure in my previous post: Manure Get the Scoop on Popular Poop!
- Add the kelp meal, rockdust, compost and worm castings. Turn over the soil amendments into about the top 6 inches of the raised bed.
- Mulch the bed with straw, leaves, grass clippings or woodchips. Find out more about types of mulch.
I have found that lasagna style sheet mulching inside the raised beds have created wonderfully light and nutritious soil. Mulching on top of the raised bed helps to retain moisture as well as slowly building fertility and soil diversity.
Of course you don’t really need to follow a raised bed soil recipe, you can create one with what you have available. I did just that for my greenhouse! You can watch my video below on how I’m building the raised bed soil in my greenhouse raised beds using what I have available on the homestead right now:
Since taking a permaculture design course, I am far more conscientious about using the resources available on and around the homestead. As such, I am currently trialling two worm composters to start producing my own worm castings from kitchen scraps. The worm composters are:
There will be more about thes worm composters on YouTube and right here on the blog next year.
Tips on Putting Raised Beds Away For Winter
Winter comes every year and there are a couple of things you can do to prepare your raised beds to maintain the rockstar soil you have just created. Using clear plastic or floating row cover with mulch over autumn and winter can help you extend your growing season and harvests if used correctly.
Over the course of the season you will probably have seen your raised beds drop in soil level. This is perfectly normal and nothing to panic over.
Before the snow arrives, it is a good idea to pull any weeds, top up the raised beds with compost or the raised bed soil mix above.
Winter is a fantastic time to add in soil amendments which need some time to break down so that they are ready for your plants in spring. Autumn and winter was traditionally when manure was added to the garden so that it would decompose over winter. I add heavily soiled bedding from the chicken coop as a mulch, the chicken manure will break down over the winter. Any material which did not decompose can be removed in spring and added to the compost bin.
It is important to mulch in winter. Mulch protects the nutrients from leaching out of your soil, helps to stabilize temperature and can help you to continue harvesting cold hardy crops in winter! Mulched beds have fewer weeds in spring as well. Popular mulching materials include:
- overwintering green manure crops such as winter rye
- plastic sheet mulch
What is your favorite way to make the best raised bed soil? I would love to hear about them in the comments!
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