My beautiful, mulched kitchen garden in July 2018.

This is the second part of my series about soil analysis here on Sara's Kitchen Garden. I decided to test three different spots in my garden, my beds outside and both of my polytunnels. I wrote more about why I wanted to do these tests and how much they cost in Part 1. Now, the results are in and I'm excited to go through them with you! I'm going to start with the beds outside and then go through the polytunnels a bit later. You can read through the test results at the bottom of this post.

Sweco Geolab did the soil analysis. The post is not sponsored, I paid for the service.

Read more about my no-dig garden: Creating new raised beds

Mulching works wonders!

In short: The soil in my garden is so good that some nutrients don't even fall within the range of the tests, the soil is simply that saturated. The soil is also extremely rich in humus. The mulched beds outside are apparently outstanding, the beds in the polytunnel are doing very well but they could be even better if I added mulch there too.

I'm a lot better at gardening than reading and analyzing charts. So, I've asked Anna Pettersson Skog who is a horticulturist at Sweco Environment AB to find out what the test results mean. Anna works with different kinds of beds, for example in cities where you need an expanded skill set in order to reach the best results possible. She has been working with these kinds of tests for a long time and also grows vegetables in her own garden. This is her verdict:

– Your mulched beds are doing great! There are plenty of nutrients in your soil, the results are very good. Mulching works very well for you. We usually don't see numbers this good on a normal day.

This is very exciting and I want to know more!

Results

Like I said before, I'll go through the results from the beds outside today and write more about the polytunnels later.

Anna is very happy with the results from the beds outside for a few reasons: The soil is very rich in both humus and nutrients. She concludes that my decision to mainly fertilize with plant material (I don't use manure) as mulch is what has transformed my soil.

Nutrients

Anna took a look at the soil conductivity (the salinity and electrical conductivity of the soil) to see how my soil is doing. She tells me that the soil in vegetable gardens usually score between 1-3, but my result is 4.9. This tells her that my soil is very rich in nutrients. You might get some problems if it passes 5 though, then seeds might not germinate and the plants might have trouble absorbing water. This is not a problem in my garden though since other parameters compensate for the high soil conductivity.

The soil analysis show that there's plenty of nitrogen, magnesium and potassium in the soil. There's a lot of fosfor in there too. You can measure the fosfor in soil from a scale of 1-5. Gardeners and farmers who have class 3 soil don't add any extra fosfor when they fertilize their soil. My soil is very rich in fosfor and is classified as over class 5. Fosfor is very important for root development and growth.

Watch a video about my mulched garden: Time to start mulching!

Humus

It's really important to have a good amount of humus in your soil, so that the nutrients stay put. I've read that good gardening soil should contain at least 10 % humus. My soil contains about 21 % humus which is just amazing! The amount of humus is a result of mulching, which keeps adding to the humus in the soil. The humus contains nutrients that will benefit the soil in the long run, like a storage. This will help the microbe and the soil will also get a really nice texture which is great for a number of reasons. Especially when it's as dry as it's been this summer, since the humus helps keep the soil moist

– 21 % humus is what you would find in soil that lays on top of old peat bogs. You could say that you have your own little bio bank in your kitchen garden, which will be very beneficial when you grow your vegetables, says Anna Pettersson Skog.

PH

My soil has a pH value of 6.3. The soil in a regular garden should  measure somewhere between 6-7. A low pH indicates that your soil is sour while a high pH value can make it more difficult for the plants to absorb the nutrients in the soil. Anna thinks that I could have a higher pH value, but it's not something I need to think too much about for the beds outside.

– You could use lime to increase the pH. But this could potentially be a bit risky. It's quite hard to lower the pH again if it's too high, so I think you are fine where you are.

Some people use ash instead of lime to increase the pH, is this something you would recommend?

– No. Using ash is not a good idea, since it might contain heavy metals.

I took the samples in May before I really got started on the mulching this year. There were thick layers of grass clippings and other plant parts on top of the soil. According to Anna, the mulching process will raise the pH on its own, just by having the microbe process the mulch and turn it into soil. Nature is truly amazing! The pH is probably a bit higher now than when I took the samples, assuming that I did the mulching right.

My own bio bank

Anna tells me that the soil outside is like a full pantry: There's plenty of nutrients for the plants when they need a quick boost and also a storage that will last longer. According to Anna, two different methods were used during the soil analysis: the AL method and the Spurway method. They might produce different results, for example regarding the nutrients. It's very convenient to use several methods when you do a soil analysis. One method might show what's available short term, while the other gives you an idea of what the long-term supply might look like. I find this very interesting!

I tell Anna about how well my vegetables were doing in the summer of 2016 and 2017. I had just given birth the first year, and my one year old kept my company in the garden the next. I didn't mulch as much as I had done the previous years, yet my garden was thriving. Which actually wasn't that strange at all, according to Anna. The mulch had created a ready supply of nutrients that the plants could use. I probably wouldn't have seen results this great if I had fertilized my vegetables some other way.

What about store-bought products?

I ask Anna what my soil would have been like if I had used regular manure or store-bought products, like mineral fertilizers.

She tells me that you can get good results using both, but you might cause nutritional imbalances with a mineral fertilizer. The fertilizer is highly concentrated and it's easy to use it the wrong way. These imbalances can cause a lot of problems for your vegetables. And your "pantry" of stored minerals won't build up the same way when you use these products. But most importantly, you won't get the same amount of humus which the soil needs to thrive.

I keep thinking that I'm doing my soil a favor by adding my old plant parts, and that it will pay off in the future too. I really use my soil, and take good care of it in turn. Knowing that I'm doing it right makes me feel very excited for the future. Especially since mulching works so well!

Keep mulching!

So, what should I do with all of this new knowledge? What can I do to make sure that my soil is just as healthy in ten years?

Well the advice I've been given is to simply keep doing what I'm doing. It's apparent that mulching works, so that's what I need to do. I have plenty of humus and nutrients in my soil and I don't really need to change anything at this point. My idea was always to imitate nature, so to speak. Using plant material seems to do the trick. So, I'm not planning on changing anything right now. But simply mulch, mulch, mulch!

The natural way

I tell Anna that I get quite a few skeptical comments about the fact that I only use plant parts, compost, nettle water and diluted urine to fertilize my soil.

– Well, nobody is making any money off these methods. A lot of people might feel provoked by the fact that you can succeed without buying any fancy products. The people who produce and sell these products believe that they have the best solutions. But your soil is thriving without them!

Mulching simply means to put plant material on top of the soil, where it breaks down and turns into new soil.

What do you think about all of this? Is mulching the best method? I realize that not all of you might be able to mulch as much as I do, but I'm guessing that most of you could do it in parts of your gardens? Why not give it a try? Mulching works!
/Sara Bäckmo

Thank you Anna Pettersson Skog for helping me make sense of the soil analysis!

*Two methods were used to analyze the soil, the AL method which looks at the long-term supply of nutrients in the soil, and the Spurway method which maps out the short-term supply. Heavy metals, humus and PH was also analyzed.

** I've been mulching my beds outside for about seven years. There are different kinds of mulch on the ground for most of the season. I've always thought that the soil is really lovely and that everything grows well here. 

The tests

The tests below are in Swedish, but the chemical symbols are the same in English too of course, so I hope you are able to get an idea of what the charts say.

*32 The beds outside

* 33 The small polytunnel

* 34 The large polytunnel

The Spurway method was used for these samples. This method measures the short-term supply of nutrients, the nutrients that the plants can utilize quickly.

Analysis of soil samples from the beds outside, according to the AL method. This method measures the long-term supply of nutrients in the soil. The top field of the chart translates to: Silt, Sand, Gravel and Rock and the granularity of the different categories, from fine to coarse.

Analysis of soil samples from the large polytunnel, according to the AL method. This method measures the long-term supply of nutrients in the soil.

Analysis of soil samples from the small polytunnel, according to the AL method. This method measures the long-term supply of nutrients in the soil.

An analysis of heavy metals in my garden. *Arsenic, Lead, Cadmium, Cobalt, Copper, Chromium, Nickel, Vanadium, Zink, Quicksilver.