As your seedlings sprout in your flats, the first greens to appear are the “seed leaves” or cotyledons. They produce food for the plant as it begins to grow true leaves and are usually distinctly different in appearance from the plant’s leaves. If you are starting your seeds in flats, once the second set of true leaves start to appear it’s time to begin potting up – transplanting your seedlings from the flats into individual containers or cells of multi-packs.

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There are a number of reasons for this. Plants left too long in flats get crowded and compete for light and root space. Long roots intertwine in flats and make it difficult to separate transplants without excessive root damage. Putting plants in individual spaces isolate the roots making the plants easier to remove from the container for final setting out, resulting in less transplant shock. And the process of potting up weeds out smaller and weaker seedlings leaving you with only the best plants for your garden.

Many types of containers can be used for potting up, the most common being the plastic multi-cell pack. I clean and reuse as many of these as I can, discarding them when they split open. Friends and neighbors that buy their garden plants are a great free source for these packs. Many types of containers can be used as long as they have sufficient room for growth, can hold up to being wet, and provide good drainage. For tomatoes and peppers I like to use a bigger container to encourage the plants to develop a larger root ball. Every spring I have the coffee drinkers where I work rinse their 8oz. foam cups and put them in a box for me. These make great individual pots and puts them to use one more time before they’re thrown out. I make sure they’re rinsed well, then using an 8 penny nail I punch 7 holes in the bottom of each for drainage.

For soil I’ll use any of a number of commercial brands and mix it with the soilless seeding mix from the flats as I transplant. Some brands now have fertilizer added which simplifies caring for the plants. Garden soil can be used, but again there is the risk of soil-borne pathogens infecting young plants. If you use your own dirt be sure to lighten it by adding some soilless mix so it won’t dry hard and crack between waterings.

I put my potting soil in a large mixing bowl to make it easy to add soilless mix and fill packs and cups. I’ll fill a pack 1/2 to 2/3s full depending on the size of the root ball on the plant I’m transplanting. Poke a finger in each cell, firming the soil to the bottom and sides and creating a well for the roots.

Now it’s time to start lifting plants from the flat. Pinch off any seedlings that are small, weak, or too close to a better seedling. You’ll be tempted to try to keep every plant, but the effort is often not worth the results. Using a dinner fork, carefully punch around the plant you are ready to move like you might take a piece of sheet cake from a pan. Lift with the fork from underneath, you will lose some roots, but it won’t matter. Remove only as much excess dirt and root as needed to fit into your container – keep the root ball as intact as possible. Place the plant in the well you created in the pack cell and spoon additional dirt around the plant. If you need to support the plant while backfilling, hold the plant by a leaf, Not the stem. If you damage a leaf the plant will probably recover. If you damage the stem, the plant will die. Firm the soil well around the plant so there are no air pockets in the cell, and continue to fill and firm until the soil level is about 1/8” below the cell walls. Don’t fill too full or the water will run into adjacent cells rather than pooling in each cell when you water.

When the pack is filled, place it in a solid tray to catch any water than may drip through, and gently water the plants in. Your plants may droop at first due to transplant shock but will soon recover. Once your tray is filled with repotted plants it’s ready to go back into your rack or growing space. Adjust the height of your lights if needed and check your seedlings daily. Packs can dry out faster than flats and some cells seem to dry more quickly than others so watch each pack carefully and water when the surface is quite dry. Again, overwatering can do more damage than underwatering, so don’t water too frequently. Continue a light fertilizing to keep the nutrients flowing to the plants. This isn’t necessary if you are using potting soil that already has fertilizer added. After a few days you’ll see your plants gaining size rapidly. Keep your lights adjusted so the tops of the plants are kept just below the bulbs.

Maintain your plants until about 1½ to 2 weeks before you plan on setting them into their final locations. At this time you’ll start the process of “hardening off”; acclimating your plants to an outdoor environment.

Happy Potting!