4-Week Old Heirloom Tomato Plants & 10 Tips for Potting Them Up

4-week heirloom tomatoes in 4" pots
4-week heirloom tomatoes in 4″ pots

I’ve had a number of requests to show the growth stages of heirloom tomato plants and pepper plants, particularly at the 4-week stage.  The 4-week stage is fairly important, as that is typically when the seedlings are outgrowing their cells and need to be potted up into larger containers to continue growing strong and vigorous for their permanent bed in the garden or large pot.  Here are some photos of the 4-week growth stage of heirloom tomatoes and tips for potting up the seedlings.

Tips for Potting up Heirloom Tomato Plants:

  1. 4-week heirloom tomatoes still in flat
    4-week heirloom tomatoes still in flat

    As you get ready to pot up young heirloom tomato plants (or pepper seedlings), a better indicator of timing than the 4-week period, is to pot them up after they have two sets of true leaves (do not count the seed leaves at the bottom).

  2. Handle the seedlings by the leaves rather than the stems.  If you tear a leaf, the plant will still grow.  If you break the tender stem, the plant is ready for the compost pile.
  3. 5-week old pepper plants
    5-week old pepper plants

    I grow my initial heirloom tomato plants in 196-cell trays, and when it is time to pot up I take a butter knife and gently pop the plant out of the cell with the soil bundle (aka a plug) intact.  Have a 4″ pot ready with moist potting soil and make a hole with your finger in the center of the 4″ pot.  Place the seedling plug into this hole and gently press the soil around it to make contact with the roots.

  4. If you grow many seedlings in one container rather than in cells, you will need to tease apart the roots from each seedling and then place in the hole of the 4″ container.  Alternatively, you can snip off the weaker seedlings at the soil line and leave the strongest plant in the container to take advantage of the nutrients in the remaining soil.  Remember…don’t handle the seedlings by the stem!
  5. Newly potted up heirloom tomato plants may look limp and stressed the first day or two.  Don’t fret and do anything drastic like fertilizing them.  They will recover with a couple days rest in the same environment they were in prior to potting up.  Keep them out of bright sunlight for a couple of days.
  6. When potting the heirloom tomato plants up to larger pots, plant them a bit deeper than they were in the cell or original container.  Additional roots will form along the buried stem and give you a more vigorous plant.  You can cover the seed leaves and plant right up to the lower set of true leaves.
  7. Use the same potting soil that you used to start your seeds…not garden soil.
  8. Water the tomato seedlings in their cells or container well BEFORE you start to pot up.  Moist soil will cling to the roots and protect them from drying out.
  9. Depending on the weather and when you are going to put the heirloom tomato plants in their permanent bed, you may want to pot up a second time.  A good rule of thumb when deciding when to do the second transplant is to wait until the height of the seedling is three times the diameter of its pot (probably around 6-10″ tall).
  10. Trouble shooting:  If your heirloom tomato seedlings are getting tall and spindly, it may be related to:
  • the light source may be too weak or too far away from the growing tip;
  • the room temperature may be too warm (I keep my daytime temperature around 70 degrees and the night temperature around 50 degrees; or
  • you are using too much fertilizer.  Just use potting soil that already has fertilizer in it or use potting soil with compost.  Wait until they are outside before getting more generous with fertilizer.
April 19, 2013 in Forest Lake, MN
April 19, 2013 in Forest Lake, MN

This is the longest, coldest winter we have had here in Minnesota, and while my heirloom tomato plants and pepper seedlings are currently quite happy in their protected environment, they will be hurting soon if we can’t get them hardened off.  It is April 19th and 4″ of new snow on the ground, and still snowing!!  Ugh.  I haven’t given up hope that we will have a long warm summer, but spring is looking pretty doubtful.  As a farmer, you do learn to roll with the punches, but I have to admit this is getting pretty depressing.