Filling, or Refreshing, Your Raised Bed Garden
Soil. We treat it like dirt. When it is actually one of the main reasons we have life on earth...
Of course you don't have to get that philosophical when thinking about your raised bed garden. But the underlying message (you're going to probably get tired of hearing about in this post) is that good soil matters for a healthy, productive garden.
You've been warned. Read on...
Filling a new bed...
For the sake of this exercise, we're going to assume you have a 4'x'8'x10" raised bed garden.
[This handy SOIL CALCULATOR can help if your bed is a different size or you want to know about filling containers.]
For a garden of this size, you'll need 0.8 cubic yards, or 21 cubic feet, of a basic mixture of topsoil and compost at a 2:1 ratio. (Or you can just get our magical custom blend Thriller Bed Filler and call it good.)
Bagged soil comes in various sizes from 16 quart, 1, 1.5 or 2 cubic feet. So you have to do a little math to divide your bag size into 21 cubic feet.
If you have multiple beds you're going to start thinking in cubic yards of soil (the equivalent of 27 cubic feet per yard). And you're probably going to want to think about a bulk order which is often the most cost effective but also kind of messy. Bulk orders are usually brought in a dump truck and put in your driveway as they cannot block city sidewalks, streets or alleys. Plus, especially now during Shelter in Place, it is sometimes hard to find a landscaping company that will deliver a "small" order (less than 10 cubic yards).
So most people resort to bagged soil which is a little more expensive but convenient to carry to the back yard...
If you want to get really dorky, look at this image below (which kind of looks like a Rubik's Cube because it is an image of a Rubik's Cube.)
A few basic points about the ingredients in your soil:
Topsoil: In Chicago, topsoil is usually gathered from fallow (unused) farmland in suburban or rural areas. Often before the property is being developed for another purpose. This topsoil may have been part of a conventional farm at one point where pesticides were used but often the land has sat fallow (unused) for many years and any pesticides have leeched out. For this reason, no product that contains topsoil can legally be called organic.
Manufactured soils: These soils are a combination of non-topsoil ingredients. These ingredients can include compost, coir (coconut fiber), peat, perlite, vermiculite, rice hulls or other ingredients. These products are called organic because the materials that go into them are, indeed, organic.
Compost: In it's simplest form, compost is rotted stuff. Rotted food scraps, rotted chicken/horse/cow/rabbit manure, rotted hay... the magical combination of time and heat (and sometimes earthworms) converts otherwise unusable materials into garden treasure. Sometimes a bag of compost may be a little "fragrant" - any smell will dissipate once you put it on/in your soil. But be forewarned if you wanted to use it on your houseplants. Another option for houseplants (and other plants) is...
Worm Castings: This sounds fancy but it's really just worm poop. All the nutrients they get from eating things in your garden (or in a worm bin) turn into the most precious of garden resources. You can buy worm castings (City Grange carries them) and they are good for houseplants and containers. You could use them in a larger garden bed but using compost is probably better bang for your buck.
Nutrients & Other Things: Good, fresh soil likely contains all the trace minerals your garden needs. But, after time, these elements get washed out of the soil or used by plants and may need to be replenished with compost or other solutions.
A familiar example of soil lacking an essential nutrient is when tomatoes suffer from "blossom end rot" which is due to a lack of calcium in the soil. A garden refreshed often with compost and organic fertilizers will generally stay productive. It's like a relationship, you have to nurture it for it to thrive.
What the heck is Mycorrhizal Fungi? Well, it's too much to go into depth here but a simple answer is fungi that work with the plants roots to help them uptake soil nutrients more effectively. Each type of plant has a different fungi it partners with so when you see a bag indicating it includes Mychorrhizal Fungi make sure the product matches your gardening need. A fungi for trees isn't going to do much good for your veggie garden.
[If you want to geek out and learn more, check out this article by Mother Earth News.]
You can spend a lifetime learning about, and tinkering with, your garden soil. There's a lot to learn. People actually study soil for a living. So consider the above the absolute basics about garden soil and be open minded to learning more as you garden year after year.
[I threw that cute illustration in of soil because we all have short attention spans these days. Cute pic! Mental break! Ok, now read on...]
WHAT ABOUT CONTAMINATED CITY SOIL (ARRRRGGGG WAILING AND GNASHING OF TEETH) You can tell I hear this a lot. And not to make light of a serious topic but the biggest thing you should worry about in soil around your house is old flakes of lead based paint vs. industrial pollution. And your kids eating soil with flakes of lead based paint in it. Want to NOT worry about this? Build a raised bed and put fresh new soil in it.
Now let's move on...
Refreshing an existing raised bed
Each spring it is wise to refresh the soil in your raised bed. Last year's plants, and sitting through the winter likely uncovered, have depleted your soil through plant uptake and leeching respectively.
But it is easy to reboot your soil in spring...
Let's go back to that 4'x8'x10" raised bed. You may notice that the soil has settled since last year. What was once a very full bed now has compacted or settled a few inches. The best way to refresh your soil is to fill up the box with a good compost.
For each inch you want to fill your bed you will need about three (3) cubic feet of compost. Easy.
Before you put it on, sift through the soil on the top and remove any twigs, rocks, old plant material or other debris that have blown in over the winter.
Open the bags and spread evenly on the top of your bed. And, with a hoe, rake or other garden tool scratch the compost in to the top few inches of the soil.
DO NOT GET ALL FARMER DAN WITH YOUR SHOVEL AND TURN THE SOIL. THIS IS BAD.
(So bad I put it in all caps.)
There's a system that develops underground in your raised bed. Channels for air and water, earthworms and other creatures, beneficial microorganisms and more magic have created a useful web of life that will benefit your garden. If you turn your soil you ruin all that and, basically, turn your beautiful soil to useless, dried out dirt.
You're not tilling up the back 40, you're gardening in a raised bed. Trust me on this. Just scratch the compost into the top few inches and call it good.
Adding All Purpose Fertilizer
Before you scratch in that new layer of compost (IN THE TOP FEW INCHES - SEE SCARY ALL BOLD STATEMENT ABOVE) you can also add an all purpose fertilizer.
We like, and carry, Down to Earth because it's a great organic product (and the packaging is adorable and compostable). They also have a VEGAN product for, well, vegan gardeners. We carry it at City Grange.
Fertilizer is a topic for another blog post but let's just say if you're growing veggies, use a veggie fertilizer. Much like the Mycorrhizal Fungi discussion above, different fertilizers do different things so using that crusty box of African Violet fertilizer under your kitchen sink probably isn't going to help much.
You apply your granular fertilizer at a rate of half cup per five SQUARE feet (we're talking about surface area now, not cubic area.) So, for your 4"x8"10" raised bed, that's 3.2 cups of fertilizer, give or take.
Well, that's enough on this topic for one blog. I hope you made it all the way to the bottom. We're available to answer more questions if you have them - just send a note to firstname.lastname@example.org