Building soil for raised beds

Kosch(6b)May 15, 2014

Hi All,

Just getting to building some raised beds for this year. One 4x10 will have beans, cucumbers, lettuce, carrots, beets, radishes, and a few other random things. Another 4x4 will have all strawberries.

Most of our landscaping companies have about the same stuff. I'm thinking some mix of their garden soil,compost, and composted bark fines. I also will have a drip irrigation setup if that matters.

I'm looking to build something based on what they have and would appreciate any input!



Here is what they have:

Premium Garden Soil�
For Vegetable and Flower Gardening -- Our special blend of black peat soil, organic compost and sand produces the best fertile soil for heavy feeders like perennials, vegetables and annuals. Our patented Premium Garden Soil is specially blended to retain moisture while providing the perfect drainage and the optimum amounts of organic matter for healthy plants. Your roses will grow healthy and strong, your flowers will be lush and colorful and your vegetables will yield a bountiful harvest when you start with Premium Garden Soil.

EKO Compost

Fresh Bark Fines
There's nothing like the clean, earthy scent of fresh bark. This finely ground red fir bark runs 1/2" and less. Its fresh reddish brown color offers a nicely manicured look to your garden and landscape beds.

Dark Bark Fines
Do you like the look of rich dark soil but want the benefits of mulch? If so, then Dark Bark Fines is a wise choice. This mulch began as fresh bark fines, but was composted to produce the dark earthy color often sought after by homeowners and contractors alike. When used directly on top of the soil, this bark can be worked in to the soil as it further decomposes and becomes a soil conditioner.

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I vote for Kimmsr's advice. He should be around tomorrow.


    Bookmark   May 15, 2014 at 3:49AM
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The description of that "garden soil" really tells you little. What you should know is the amount of mineral particles (in the 92 to 95 percent range) and how much organic matter (in the 5 to 8 percent range) is in that mix. If the "garden soil" has organic matter in that 5 to 8 percent range you should not need to purchase compost, this year.

What to use for mulch is always a dilemma and I much prefer what is available and at low cost, preferably free. To be effective at controlling unwanted plant growth from the soil that mulch needs to be at least 3 inches thick. Mulches can be thinner if a sunblock such as newspaper or cardboard is used. There is no advantage to composting mulch material so if the composted mulch material is more expensive you can pass that up.

    Bookmark   May 15, 2014 at 6:19AM
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For my raised beds I used a mixture of Mirical Grow Garden soil (which is too hard when used alone), MG top soil, humus/manure and and leaf compost. The combination was 2 parts garden soil, 1 part top soil, 1 part humus/manure and 2 parts leaf compost. Finally after the beds are planted I mulch them with shredded leaf compost that is turned under the next year. Seems to work well; here is last year's growing plants.

    Bookmark   May 15, 2014 at 6:33AM
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You do want SOIL for a raised bed, not just compost or mulch. Plants may grow in an all-organic-matter material but it will continue to decompose and sink down. If whatever soil you get has a lot of organic matter, you can just go with that; if not, amend with compost as you put it in.

    Bookmark   May 15, 2014 at 11:57AM
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Okay thanks for that all! I'll see if I can find some better specs from the company as to what is in the soil. I know I need soil, just wasn't sure if I should mix in some additional compost.

I was mentioning the bark fines because I've seen some mixing it into their raised beds, I think similar to the 5-1-1 mix. I'm just not sure if that is to help with drainage or what.


    Bookmark   May 15, 2014 at 1:33PM
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johns.coastal.patio(USDA 10b, Sunset 24)

Many folk use 50:50 mixes of soil and organic matter. Yes, that is an opportunity to keep it up and add more and more compost in yearly maintenance. Great.

Because if you only shoot for the organic content in good soil (less than 8%), why are you doing a raised bed exactly? Is it just for accessibility or neatness?

Update: I think I found your supplier (Wittkopf), and sure if their Premium Garden Soil has reasonable ratios, and I'd be somewhat flexible on that, I'd go for it. You can even ask them for references. Happy landscape designers. Never hurts.

This post was edited by johns.coastal.patio on Thu, May 15, 14 at 20:17

    Bookmark   May 15, 2014 at 8:00PM
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I'm trusting Kimmsr. Kimmsr, can you please provide a link that 8% compost in a raised bed is the magic number ? I think this has worked for me because the beds are rather tall.

I'm guessing that most of my beds are between 8%-20% organic matter, and between 1 and 2 feet high (80/20 -92/8). I leave old, fine feeder roots to decompose, and don't till the soil after the first year.

In most of the beds, I started with a 60/40 soil/compost mix, and never amended the soil again. I do lay down various rotting vegetative matter whenever it becomes available (free).

Most of my beds contain up to 10% lava sand. Lava sand is the one material I use that I cannot explain why it works. It has a tremendous amount of surface area and is paramagnetic.

I'll try to find a link sometime with experiments that demonstrate how roots grow better with a small percent of it in the substrate. (It's funcion is not drainage, it's a completely unique material.)

The easiest way to make a bed and I believe is superior, is to use native mineral soil (right off of the property, if possible), mixed in with compost (plus mulch on top). I prefer mulches that contain no pine bark.

I'd like to know how you came up with that number, Kimmsr, as it seems reasonable to me.


This post was edited by Mackel-in-DFW on Fri, May 16, 14 at 1:55

    Bookmark   May 16, 2014 at 12:45AM
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Most every thing I have seen over the years from the universities says soil should have, or the optimal level of organic matter is, 5 percent organic matter. However, the testing of my soil over the years has been in the 6 to 8 percent range and the plants grow most bestest at that level, in my soil. That is also the level I have gotten soils in NW Indiana and SE Ohio and plants thrive there as well with that level of organic matter.
I also know, from other peoples gardens, that when the level of organic matter in soils drops below 5 percent problems with insects and plant diseases increases. I also know that when the level of organic matter in soils is much above around 10 percent the soil often holds too much moisture and plants roots show signs of rotting if close attention to moisture levels is not maintained.
I have used these simple soil tests,

  1. Soil test for organic matter. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. For example, a good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drainsâ too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer your soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.
for many years along with sending soil samples to MSU for pH and major nutrient testing. These are all tools to help the gardener know as much as possible about the soil they are planting in.

    Bookmark   May 16, 2014 at 6:51AM
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Got it, Kimmsr, and agreed. But I'm referrring to raised beds. It's okay if you don't have immediate access to a link that specificaly refers to that...


    Bookmark   May 16, 2014 at 9:26AM
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johns.coastal.patio(USDA 10b, Sunset 24)

Doing some surfing, I see college extensions folk, and master gardener groups, using as varied of mixes as we are talking about here. Sure, some are at the low end with 10% organic matter, but some are up at 50% as well, sometimes even higher.

I suspect that they all work.

Though I think "do you really know why you are doing a raised bed?" is an important question. If it is just a garden feature, with soil of the sort you could improve in flat ground, that's fine. But knowing that you may not have to import so much "bed mix."

    Bookmark   May 16, 2014 at 10:14AM
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