Container Gardening in Cold Climates: Soil control

My plan for today’s post was to talk about all of the different caveats that come with container gardening in the north, but after typing for several hours on dirt in containers, I had realized that this topic should be broken up into several posts. This topic of northern container gardening is going to be split up over the next few weeks to allow me to dive deeper into each topic, and what better way to start than where all plants have to start with: the dirt.

First, I need to clarify with these tips on container gardening, I am not referring to raised beds which can be considered very similar to container gardening, but has some key differences with how it relates to the plants. Raised beds are still connected to the ground via an open bottom to the container, which allows for the soil’s beneficial insects, bacteria, and fungus to enter the bed and provide nutrients to the plant. This is a much more complicated subject, but all you need to remember is that plant’s have a relationship with the microbes in the ground that provides more support for in-ground plants. In containers, you have to supplement for this lack of resources with more frequent fertilizing and watering.

This brings me to my first major point with container gardening which is soil control: The good news and the bad news is you have way more responsibility with it in a container. You no longer get as many of the beneficial aspects of the microbes even if you use mostly organic gardening strategies with containers. However, if you want to grow plants that are not suitable for the ground you have access too, then this additional control is wonderful! For example, some plants like blueberries and cranberries need to have very very acidic soil that most people don’t have in their yard but with some simple amendments to the container soil, they can be grown easily. There are two major concerns with soil control in the container, which is fertilizer and water. Obviously, plants will go through fertilizer in their container very quickly and will benefit from more frequent fertilizing than in-ground plants. However, it is also important to not over-fertilize the plant as this can cause burning of the roots/leaves (if using inorganic fertilizer) or can cause diseases (if using organic fertilizer). This is typically why container fruits are recommended to get a light dose of fertilizer every week or two during the growing season regardless of the type of fertilizer you use. How much fertilizer you use will depend on the plant, the size of the plant, and the size of the container.

The other big consideration with soil control is the ability for the soil to retain moisture. Having less soil, container plants are going to dry out much more quickly. If you have tried growing a tomato in a container, you will know this very well as you have to water it almost daily. However, most containers you will use will probably be plastic or glazed pots which won’t allow moisture to wick out of the walls of the container which is a huge help for retaining moisture, but can also hold onto too much moisture and cause the roots to rot. You may want to consider using one of these types of pots if growing a plant that prefers wetter soils or if the plant is very big for the pot. Using fabric or non-glazed terracotta will also allow for more moisture wicking from the soil, which can be very useful for plants that want dryer soil.

How you water is also important with containers. Dry soil is hydrophobic and does not actually hold water very well, but slightly damp soil is a sponge and will soak up a surprising amount of water. This phenomena is why when a plant is completely dry and you throw the water hose at it for several minutes at full blast, but the plant is still dry: when the soil gets too dry, you have to water slowly to allow for the most moisture to stay in the soil. The soil constantly flipping between the bone-dry and sopping wet extremes is also a great way to encourage different diseases and issues with your plants. This is why many gardeners will use drip irrigation to water efficiently. However, not everyone has the knowhow or the number of plants to warrant a drip irrigation system. My favorite solution is taking a plastic bottle and poking a small hole in the cap, then placing the bottle upside down in the container: this allows for a measured amount of water to be slowly dripped into the soil, which allows for more steady moisture absorption.

Above all else, learning the proper soil parameters for your different plants is going to come down to research and trial-and-error. Join us next week for the next topic in this series.

Thanks for reading!

Jeremy