Red plastic cups, not just for beer parties

It’s time to pot up the tomato seedlings into larger containers. I usually do this 3 to 4 weeks before my planting date. Because I over-plant my flats, I need to separate and pot up the seedlings to give them more room to grow. Right now, the tomatoes are about 4 inches tall after 4 weeks in the 6 packs. I could clip out all but one plant per cell and leave them in the 6 packs, but they will quickly get root-bound and slow their growth. I can grow a much larger, healthier plant by giving it more room. The average 6-pack grown tomato would be 6 to 8 inches tall. In the cup, it would double that size.

Several years ago, I got a deal on those 4 inch green grow pots. I paid 10 cents each for about 100 of them. When I ran out, I realized what a deal that was. To replace them would cost about 25 cents each, so I looked for an alternative. While shopping at Costco, I found a package of 240 red Dixie 16 oz. cups for $15.00, that’s about 6 cents each.  They worked great. The cups are inexpensive, sturdy, easy to clean and reusable. I am still using the cups I bought about 7 years ago.

The easiest way I found to get drainage holes in the cup was to melt it with a candle flame. Hold the bottom edge of the cup briefly above the flame. It only takes a second to melt a half inch hole. Turn the cup and melt two more. Be careful not to put the cup in the flame, it can catch fire and that hole would be be waaaay too big.

That’s it. Perfect drainage holes along the bottom edge of the cup.

Melt 3 holes in the bottom edge of the cup for drainage

Melt 3 holes in the bottom edge of the cup for drainage

The cups hold the same volume of soil as the 4 inch pots, but because it is deeper, the roots can really get going before hitting bottom, start growing in circles and become root-bound.

When potting up, I use the same Pro-Mix BX potting mix, but I don’t screen it like I did with the seeds. Each flat cell has 2 or 3 seedlings in it. Gently put apart the root ball to separate the seedlings. Don’t worry about ripping some roots, tomatoes are resilient.  Fill the cup about 1/3 full and press a seedling down into the soil mix. Fill in around the plant while holding it in the center. Gently tamp down the soil around the plant while filling the cup. When you’re done, only the leaves are visible. New roots will grow along the buried stem and make a nice sturdy plant.

Newly potted tomatoes

All ready to party with the festive red cups.

Don’t forget to write the variety on the side of the cup with a Sharpie. After planting, the cups can be washed, the markings can be easily removed with rubbing alcohol ans stored away until next year’s potting party.

A standard tray will hold 15 cups. After I give the plants a good drink with half strength liquid fertilizer, the trays are kept in a shaded area of the greenhouse for a couple of days. The plants will need to be checked twice a day, especially on sunny days when it can dry out quickly. The trays without holes allow for bottom watering, so on those hot days, keep an inch of water in the trays. I’ll move the trays to full sun gradually over a a few days’ time.


Shaded by the shelf above, the plants get used to their new party cups in the greenhouse.

I ran out of trays, so some of the seedlings are still in the 6 packs. I ordered more trays and should have them in a few days.

When the weather allows, the plants can be moved outside for the day to feel the wind in their leaves. This helps the plants develop good, sturdy wind resistant stems. Avoid full sun while they are out of the greenhouse until they are fully hardened off. More on that later.


2 responses to this post.

  1. Jrzy, this is brilliant!!


  2. Posted by Dan K. on May 4, 2013 at 3:26 pm

    Excellent! Plenty of room for growing strong roots and a simple answer to drainage. I use plastic yogurt cups myself (drilling 3 holes in the bottom of each one) but I may be using your idea for larger plants in the future. Thanks for the tip.


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