I use plastic cups for most things, they are taller than cell packs so more room for roots without taking up additional room under my lights. I also find them easier to wash and reuse than the cell packs.

I germinate most things in 3oz plastic cups and use that size for the initial transplanting too. Depending on the type, I will start 3-6 seeds per cup and then when they begin growing true leaves divide them into individual containers. Lettuce I usually transplant out quite small (2weeks), so they stay in the 3 oz. or if they are staying in the pots longer, I use 4" cow manure pots and then plant the entire pot. Broccoli & Cauliflower, move into 9 or 12 oz cups and get transplanted out at 4-5 weeks, Tomatoes get transplanted twice, 9 oz cups, and then 16 oz and get transplanted out at 6-7 weeks. Peppers and Eggplant also 9oz then 16 oz and get transplanted out at 10-12 weeks.

Peas I soak in water for a few hours, then use the 3oz cups, but plant them out as soon as they start to sprout - less than a week.

Beans I also soak for a few hours, germinate in 3oz cups and as soon as they sprout move them to 4" cow manure pots and plant them out at about 2-3 weeks. I also use the cow manure pots for melons and sometimes cukes.

My experience is the cow manure pots work much better than peat pots for things you dont want to stress when transplanting out. They do actually dissolve in the soil quickly, so no removal is needed except the top edge of the pot if it is above the soil line.

You cant treat everything the same and you really cant avoid transplanting if you are starting early. Putting a tiny little tomato transplants in a 16oz cup would make it impossible to keep it the moisture level right. Plus, Tomatoes like being transplanted it stimulates root growth.

This is only my 4th year growing from seed under lights so I am still learning, most of what I have learned has come from the GW forums.

Mandolls:

Your post is very helpful. Thank you. I also use cheap plastic cups for ease, cost and reuse. I am growing tomatoes from seed for the first time and the first true leaves are just coming in. I have 7 oz cups with a nice depth I plan to use. I would not have guessed needing a transplant to a size as large as 16 oz, but the room for root growth must be welcome.

What criteria do you use to determine when to make the switch from the 9 oz to 16 oz cups? Is it a growth marker analogous to them getting the first leaves, or based on time since sowing seed primarily?

Thanks in advance.

Pintoks - I use the height of the plant as the deciding factor. When the tomato plant height is about one and a half times the height of the cup I transplant it up. It happens faster than you might think, even with decent lighting.

Also when repotting it, you can bury more of the stem (plant it deeper) - tomatoes will root out along the stem, and you will have more root mass when it moves out to the garden. The tomato forum here is full of info, you should check it out if you havent already.

I spotted some 20 oz styrofoam cups at the store the other day and plan on using those for my tomatoes this year. My lighting set-up gets really crowded by mid May, but using extra tall containers doesnt take up extra space, its the wider pots that makes it hard to squeeze things in.

When the broccoli and cauliflower is repotted from the 3 oz. cup to the 9-12 oz. cup how many sets of true leaves should it have?

How many sets of true leaves should the pepper, tomato and eggplant seedlings have when repotted from the 3 oz. cup to the 9 oz. cup? When repotted from the 9 oz. cup to the 16 oz. cup how many sets of true leaves should the tomatoes, peppers, and eggplant have?

I plan to do asian greens (asian cabbage mostly) and swiss chard as seedling transplants too. I know they don't like having their roots disturbed when transplanting and are more finicky with transplanting in general. I will use cow pots for them, but since they don't like to be transplanted, they won't be repotted while being grown as transplants indoors. So what size cow pot should I use for them? They will be about 2-4 weeks old when transplanted outdoors.

Swiss chard grows well direct seeded.

To test when to transplant container seedlings, gently knock plant up and out. If roots take up all of soil, then transplant. If you transplant too soon, the plant spends time growing roots to fill container.

If plant needs constant watering, transplant to bigger container. Or just time growth to plant directly outdoors from the first container and avoid all that transplanting work.

After you've been at it for a few years, you will learn a lot from your notes. Keep a pad handy with notes like "start __ later" or "use bigger container for ___."