Spacing and Timing for Indoor Seed Starting

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Posted by @Joannabanana on
Even after many years of starting seeds indoors, I make the same mistake year after year. I inevitably run out of room. Partly because I sow way too many plants (can’t help it), but truly, I have not planned my spacing appropriately


Here are a few tips that I would like to share. 

Plan Your Crops

1.     When to sow:  Find out what your area’s Average Last Frost date is.  From that date, count back the weeks as per the recommendation on the seed package instructions.  I have a calendar where I mark the weeks backwards and have it hung near my seed starting area for a handy reference.

2.     If you are sowing into multi-cell trays, most plants will need to be transplanted into bigger pots within 4 – 5 weeks from germination.  Keeping that in mind, your newly sowed trays will be sharing the indoor space.

3.     How many trays do you have room for?  It is so misconceiving when you sow your seed starting propagation trays.  A common size for a seeding tray has 72  (about 1-1/2”)  cells; that’s 72 plants that will require transplanting into bigger pots within 4 to 5 weeks.  Fast forward 4 to 5 weeks and you will need space for 4 trays instead of one. 

No room to transplant into bigger pots

2012-02-12/Joannabanana/836ce9 2012-02-12/Joannabanana/e3b3fc

Choosing Your Starter Trays/Pots 

1.     Rule of thumb:  If the seed is small, the seedling will be small.  Small seeds started in 72-cell will accommodate the seedling usually for up to 5 weeks. Bigger seeds should be started in 2.5” or larger.

Petunias transplanted into larger pots 5 weeks from sowing

2012-02-12/Joannabanana/ab1b56 2012-02-12/Joannabanana/59df0f

2.     Choose deep-celled trays.  The deeper the cells, the easier to maintain.  3” “plus” height is great.   Anything shorter will be higher maintenance to keep hydrated.

Moving Out

I start most of my seeds indoors and then move them to a heated greenhouse until it is safe to plant them outdoors.  The petunias stay in the heated greenhouse for 6 to 8 weeks.


As you can see, I also have issues with spacing in my greenhouse as well.

Comments and Discussion
Thread Title Last Reply Replies
Greenhouse by doncarchr Mar 26, 2012 8:49 PM 1
Thanks! by Patti1957 Mar 5, 2012 7:27 PM 18
Seed trays by monalisa18 Mar 3, 2012 11:01 AM 1

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