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Step-By-Step How to Build a Grow Box From a Plastic Container

Building your own grow box is a versatile project that lets you start seeds indoors and get a jump on the upcoming gardening season. You can use common household items to create this indoor mini-bed for planting your seeds. The best time to start seeds indoors is to count backward from your area’s last expected frost date the same amount of days listed for germination on the seed packet. Your plants will then be large enough to transplant soon after last frost date has arrived. You can also use these to place inside your grow house.

The main reason to use this technique is to save money in the long run, while recycling.

Things You’ll Need

  • Shallow plastic container
  • Mild dish detergent
  • Water
  • Chlorine bleach
  • Scissors
  • Commercial germination medium
  • Bucket
  • Plastic grocery bag
  • Instructions

How To Build Your Own Grow Box

  1. Choose a shallow plastic container of any kind, or use a taller container, such as a gallon milk jug, and cut the top off with scissors to make it about 4 inches tall.
  2. Wash the plastic container in mild dish detergent and water. Rinse it with water, and then submerge it in a solution of 1 part chlorine bleach and 9 parts water. Allow the container to disinfect for about 10 minutes. Rinse it well, and allow it to air dry.
  3. Use scissors to make several drainage holes in the bottom of the container by poking the points through. Space the holes about 3 inches apart in all directions.
  4. Pour commercial germination medium into a bucket, and soak it thoroughly with water. Allow it to expand in the water for about 10 minutes. Fill the container with wet medium so it’s about three-quarters full. Follow the planting instructions on your seed packet for the planting depth, spacing and how much soil to place on top of the seeds for germination.
  5. Insert your plastic grow box into a plastic grocery bag, and tie the top together tightly. Place the grow box in a sunny windowsill where the temperature remains constant at 68 to 70 degrees Fahrenheit. If your home is cold, consider using a heat mat.
  6. Remove the plastic bag as soon as you see seeds sprouting. Keep the soil moist, and separate the seedlings when the second set of leaves appear. Transplant your seedlings into larger pots or into the garden.

Tips & Warnings

  • The plastic grocery bag sealed over the container holds humidity and moisture inside, so you don’t need to water the seedlings until they emerge from the soil.
  • Do not mix seed varieties in one container unless the germination date is the same for all of them.
  • Keep soil moist in your grow box, but not wet. Wet soil promotes fungal infections and causes root rot.