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Best Soil for Container Gardening

Soil is the foundation for which plants grow. When you are gardening in containers, your plants rely on you, as the gardener, to provide them with the best soil for container gardening for optimal growth. The best soil for container gardening can be attained by layering different types of soils, organic fertilizers, and organic soil amendments.

Check out our guide for developing robust and fertile soil organically to benefit your plants throughout the gardening season.

Growing in Felt Pots

One type of container to consider when growing is felt pots and grow bags. They come in a wide array of sizes from 5 to 30 gallons or more. They are increasing in popularity because they provide important benefits to gardeners and plants.

Benefits of Growing in Felt Pots

  • Airflow can help to regulate temperature.
  • Plant root systems self prune when they reach the fabric pot, which helps plants not to become root-bound.
  • Top-notch drainage to avoid wet feet and overwatering.
  • Handles on pots allow for easy carrying.

*Note that the increased airflow can dry out the soil in felt pots and grow bags more quickly, so keep track of your watering throughout the growing season.

Layering Soil in a Container Garden

The best soil for container gardening includes a few different key elements.

  • Composted Chicken Manure
  • Slow-release organic granular fertilizer
  • Potting Mix
  • Worm Castings
  • Compost
  • Mulch

Determining How Much Soil You’ll Need

Once you’ve acquired your containers or grow bags, it’s essential to calculate how much soil you will need to attain the best soil for container gardening. This way, you can purchase all of your materials at once without having to run back and forth to the garden center.

Kellogg Garden has a soil calculator tool that can help you determine exactly what you need to start layering your soil. You can plug in the diameter of the pot times the depth of the pot, and the tool will let you know how much soil your container requires.

Using Raised Bed Soil in Containers

Raised bed soil has thicker particles of decomposed forest materials which will continue to build the soil as it breaks down over time.  It also limits compaction and allows roots to flow in and around particles.

*Pro Tip from Bridget: If you fold down the top rim of the fabric grow bag before layering your soil, it may provide more structural support to the bag as you fill it.

  • Add a healthy layer of several inches of raised bed soil to the bottom of the felt pot.
  • While you can dump soil into the grow bag, it is recommended that you do it manually, so break up any clumps of organic matter that have formed in the soil bag.
  • You may come across the presence of a white or gray mold. “The white or gray mold is Saprophyte, which is what is naturally found on the forest floor. It is not harmful to humans or plants. It’s actually a good thing! It proves that there is life in the soil.”

Adding Fertilizer to a Container Garden

The best soil for container gardening provides adequate nutrition for plants to use as they need it. As your plants grow, the roots will spread and seek out additional nutrients. You can provide them with what they need to thrive by layering some organic fertilizer into your grow bag midway through.

  • Add a couple of inches of decomposed chicken manure and mix it a bit to incorporate the rich organic matter into the soil. This will release nitrogen slowly into the soil and increases soil fertility.
  • Add some more raised bed soil to the pot.
  • Add a slow-release, granular organic fertilizer, which will replenish nutrients over time.

Topping off Your Pot with Potting Mix

Finishing off your container with a couple of inches of potting mix can better facilitate the direct sowing of seeds and make for a more successful germination process. The potting mix contains finer particles and a fluffier planting medium which is best for seed starting.

Amending Soil with Worm Castings

Worm castings are a fantastic addition to your soil concoctions. Even if you think you have the best soil for container gardening already, worm castings can make your soil even more robust. When you amend your soil with worm castings, you benefit the soil in many ways.

  • Add minerals and nutrients
  • Combat soil born diseases
  • Help deter pests

Seed Starting Tips in a Container Garden

Now that you have created the best soil for container gardening, it’s time to plant your seeds. Bridget shared some great seed starting tips when growing in containers and grow bags.

  1. Moisten the soil before direct sowing so that you do not disrupt the seeds once they are sown.
  2. Plant seeds spaced out two times the width or diameter of the seed.
  3. Place seeds on top of the soil and then use a sifter to add a light layer of potting mix over top of the soil.
  4. Keep soil evenly moist throughout the germination period.
  5. Make sure that there is adequate airflow to keep fungal growth at bay.

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tomato plants growing in large black containers
container full of soil with soil bag in the background

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