It’s that time of year when just about every client is asking Is it too late to mulch my beds? or What kind of fertilizer should I put on my plants? or I just read I need to lime my garden to make it sweet; what does that mean? Now that a few winter bloomers are showing their stuff, the sun is making an occasional reappearance, newspapers are running “what to do in the garden this month” pieces, and the Northwest Flower & Garden Show is opening in 3 days, the race to dive into spring is on in Seattle. And, soil care is a good place to focus.
Simple At-Home Soil Test Kit
When I get these soil care questions — even if the fertilizer question is about a plant, I consider it a soil issue — I try to start by educating clients on how plants interact with soil at different times. That explanation is a little deeper than I’m going to go into here, but let’s start by answering the three questions listed above.
The first answer to all of these questions is to ask whether the client has tested their soil. Without knowing what is already going on with the soil, it’s nearly impossible to generalize about what should be added to it. Pick up a simple at-home soil test kit for under $20 here.
Is it too late to mulch my beds? It isn’t too late to add composted mulch to beds to top dress them. Heck, I find myself out spreading mulch in all seasons. Mulch does more than just add nutrients to the soil. It also encourages soil microbia to establish healthy populations in the garden, and their work builds soil tilth. As well, it protects roots and discourages weeds. So, yes, mulching can be done now. However, mulch alone may not solve every garden issue. As well, too much woody mulch (for instance) can change the soil’s nutrient and pH balance over time. So, again, testing your soil is a good idea.
What kind of fertilizer should I put on my plants? My first response to this question is don’t add a fertilizer now. If you intend to quick feed your plants, right now isn’t the time to do it. When the soil is cold and plants are still dormant for winter, fertilizers just plain don’t work. Plants don’t use the material, so you waste money putting them down. Plus, the fertilizers then leach through out soils and into the water tables with a little help from all our winter rains. So, don’t try to add fertilizers to your soil now. However, now is a good time to take soil samples to send out to a lab or test at home with a small soil testing kit to get an understanding of what your soil macro (and possibly micro) nutrient needs are.
Last weekend, I used my soil core sampler to take several soil cores from my own garden. My biggest curiosity is about beds for edibles. By growing plants that I expect to yield food, I’m asking a lot of the soil. I’m taking a lot of the nutrient value from it over and over, so it’s important that I figure out what I need to give back to it to ensure good harvests and a healthy long term eco-system.
I kept each soil sample for each section of the garden isolated in an open bag. I let the soil dry out for a week, and sifted out much of the organic matter. I then ran three simple tests on the samples from each area of the garden: one for pH, one for Nitrogen (N), one for Phosphorus (P), and one for Potash/Potassium(K). Although I tested from three different areas of the garden, I learned that in general my garden is Nitrogen deficient, has varying deficient/adequate levels of Phosphorus, and has an abundance of Potash. Knowing this, I’m able to then select what to add to the garden beds later in the season to adjust the Nitrogen and Phosphorus deficiencies.
Because I want to add a slow release material that won’t leach right though the soil, and because I don’t want to add a lot of Potassium, I’ll probably be adding something like a blood & bone meal amendment a little later in the season. (Honestly, I’m still looking over my options and prices, so look for more thoughts on this later. Worm teas and some seed meals may be other nice options.) Since I’ll be adding slower release materials, I will want to add them to these beds just as the soil warms a bit. This is when the soil microbia as well as the plant roots begin to seek out these materials. As the soil microbia process the materials, their excretions will contain nutrients in forms that plant roots will happily take up.
pH ~ 6.5 = Slightly Acidic & Great for Most Edibles
But, before I gave up on doing anything with my soil this season, I also wanted to look at the pH of my soil. In the Seattle area our soils tend to run acidic. Rain and leaching contributes to that trend. Many plants live happily in the slightly acidic to neutral range, but too acidic and plants just won’t thrive. Primarily, when living in a pH range they don’t like, they won’t be able to take up soil nutrients/fertilizers properly. So, they won’t thrive. Plus, any nutrients we add to the soil again will just leach out into the water table. It’s a waste.
A pH test is about the easiest test you can run at home. I don’t like the electronic soil test meters. I find they register the same thing everywhere. A little chemistry kit that runs less than $10 will tell you your pH.
When I ran my pH test, my soil was very acidic in a bed that had been filled with acid-loving rhodies and camellias; it came in at 5.0. My other beds came in around 6.3-6.5, which is slightly acidic and generally good for the edibles I plan to plant in these beds. The bed running 5.0 will need to be adjusted by adding lime.
It is very important to test soil before randomly adding lime, which I know many gardeners “just do”. Which kind of lime you add, how much, when you add it, and what you mix (or don’t mix) it with, is important. Too much lime, and your garden may start trending toward alkaline. Less of the plants that we like to grow in our area will thrive in alkaline soils than will in acidic/neutral soils. Plus, depending on the kind of lime you add, you can have a rapid conversion that doesn’t last a long time or a slow conversion that lasts a long time. Knowing what kind of lime you’re adding, and when is very important. But, mostly, you should verify whether you need the lime or not in the first place. And, finally, it is important to add lime before you add composts and fertilizers to the soil. Lime can take anywhere from 2 weeks to a month to start doing its job, and it needs water to do so. This means the lime can/should be added around this time of year while our rains are still steady and before the time arrives to start adding fertilizing soil amendments to the garden.
I realize this article may leave you with more questions than answers. Heck, I didn’t even get into testing for soil texture/amount of sand, silt, clay in the soil. That’s a whole other soil science discussion. If you’ve got lingering questions about your own garden soil or soil testing, feel free to post them here or sign up for a garden coaching session for help learning more in person, in your own garden spaces.
