The most important part of container gardening is the soil used in the containers. To ensure good plant growth, it’s critical to start with high-quality potting soil that is rich in nutrients and has the structure needed for prolific root growth. Over time though, the nutrients are depleted from potting soil and need to be replaced, and other important properties such as pH and water holding capacity may change.
If you are reusing soil from year to year, it’s a smart idea to make sure the soil in your container garden is up to par at the beginning of the growing season before planting.
Potting soil, while it may seem like a simple component, plays many roles. It acts as a reservoir, holding moisture and nutrients around the plants’ roots. It provides airspace in the root zone to provide roots with oxygen to “breathe”. It also provides support and stabilizes the plants by anchoring their roots.
In order to get the most out of your container garden, it’s imperative the potting soil is good quality and can serve all the functions it’s supposed to.
Commercial grade potting soil isn’t meant to be reused over and over, as it changes over time with its fertility decreasing. Over time, organic matter breaks down, resulting in a change in pH and the sources of nutrients in it are depleted either through plant uptake or leaching. Breakdown of organic matter will also affect the water holding capacity of the potting soil, causing it to retain less water.
That doesn’t mean you can’t reuse potting soil. Instead, it means you should check a couple of its qualities beforehand, amend if necessary, make sure it’s free of pests, and give it a good dose of fertilizer to replenish nutrients.
Normally, a soil would be tested to check the pH and the levels of plant essential nutrients (nitrogen, phosphorus, potassium, calcium, sulfur, magnesium, boron, manganese, zinc, molybdenum, iron, boron, chlorine, and nickel) to determine how fertile it is.
Unlike traditional mineral soils, potting soil is much more difficult to check the nutrient content of. Home soil testing kits won’t work efficiently, since the soil will absorb most of the solution you need to add from the kit, rendering results difficult to get. Sending a sample off to a lab for formal testing is cost prohibitive – it would be about the same price to purchase all new soil and start fresh.
It’s also important to check the water holding capacity of the soil before reusing it. Take some of your potting soil and fill a medium-sized container, then water it well, watching how quickly (or slowly) the water drains out the drainage holes.
Let it sit where your container garden will be for a couple days and then check on it. If it is still soggy, it needs to have construction grade sand or vermiculite added to make it more “fluffy” and allow the water to drain. Super dry potting soil would benefit from having a heavy dose of finished compost mixed in to add organic matter.
After you get an idea of what the soil pH and water holding capacity is, you can prepare your container garden soil to use in another season.
Before planting for the season, the best thing to do is to dump all of the container soil out and ameliorate it as one big pile. If you don’t have a large basin or tub to do this in, it’s possible to empty containers onto a large, clean tarp and use that as your work surface.
To facilitate moving large pots, heavy duty rolling plant caddies can be used to transport them easily around your yard without hurting yourself from the weight.
Here’s how to go about improving your container soil:
After you’ve baked the soil and spruced it back up so it’s nice and fertile again, fill up your containers and get to planting.
The soil used in your container garden is one of the most important attributes leading to how well your plants grow. Commercially purchased potting soils are formulated specifically to provide the nutrients plants need, with a light, airy structure that allows air circulation around the roots whilst supporting the plants upright.
Potting soil is meant to be used for a single growing season and then replaced, but it is possible to reuse it by making sure it is free of pests and diseases and testing the soil to check nutrient content before planting.
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