How to Have Tomato Transplants Ready for Your Garden in 6 Weeks - Container Size Matters

Growing tomato transplants isn't really difficult once you have the basics down. It just takes some time to learn. However, growing large plants in 6 weeks, that are ready to be planted into a garden, can be challenging. The key is container size. Lighting, watering, and fertilizing will impact plant growth but cell or container size is often over looked. Generally speaking, a transplant's size is constrained by the growing space of the roots. The stronger and larger the root system, the more quickly the plant can grow in size. A lot has been written about lighting, watering, and fertilizing. I thought I would show you how container size impacts the growth of your tomato transplants. 

Here are several tomato plants that were all started on the same day with starting mix, lighting, watering, and fertilizing all being equal. The only difference is the size of the cells in which they were grown. The seeds were started on November 24th and today's date is December 29th. That is 5 weeks. You can see how the seeds started in the larger 6 pack, on the right, are much bigger plants. The roots had more room to grow and expand. Therefore, their overall growth/size is significantly larger than the other plants. The tomato transplants in the middle had more space for root growth than the plants on the left. You can also see a size difference in those plants.

Room for roots is the 'overlooked' key to getting transplants garden ready in 6 weeks. The plants on the left and in the middle are really ready to be potted up into larger containers and need a couple more weeks of growth. Starting plants in larger cells not only brings you larger transplants over the same time period, it can save you time, by removing the need to up-pot/repot plants. The container size you choose, to start your tomato transplants in, is really a function of space available under your grow-lights and the amount of transplants you are growing.

 

The plants were watered equally and were fertilized around the 2 week and 4 week mark with a diluted water soluble fertilizer. The next step for the 5 week old plants, on the right, is acclimation to the the outdoor sun. Since seed starts are grown indoors, they do not have protection from the ultraviolet rays of the sun. They need to be slowly exposed to the sun and elements over a 7 day period. This additional week of acclimation brings the plants to 6 weeks of growth. They would be ready to go into the ground, if my ground wasn't frozen. Keep in mind that tomato transplants are best grown in soil that has reached 50 degrees and when the danger of frost has well passed. Here is the video that goes along with this blog post.

The pictures below show how the root systems filled the actual growing space of the large, medium, and small cells almost equally over 5 weeks. The root growth is more expansive when the plants are given more starting mix to grow within from the start.  That is, there are more roots and root surface area in the larger cell. You can see how growth was restricted due to space limitations. Smaller cells do restrict the growth of the stem and leaves by limiting root growth or expansion.. Each cell type has value based on what you are growing, your space, and timing for getting plants into the garden.

You can find seed starting products at my seed and garden shop: Starting Cell & Flats. The largest cell in the this post is listed as Medium Cells at my shop.

Alternatives to purchasing cells could be recycled yogurt containers, cut water bottles, repurposed nursery pots or any plastic container. Make sure you place holes in the containers for drainage. Root systems of your transplants will quickly grow and expand to fill the space of the containers you use. The more root growth you have to start, the more top growth you get. Addressing root growth will allow you to grow large tomato transplants in 6 weeks.