With the success of putting 8 holes in the rockwool from this experiment, I decided to max out the holes with seeds and see what happens.  I poked 8 holes in 5 rockwool cubes and planted the following:

Rockwool #1 – 2 seeds per hole
Rockwool #2 – 3 seeds per hole
Rockwool #3 – 4 seeds per hole
Rockwool #4 – 5 seeds per hole
Rockwool #5 – 6 seeds per hole

If needed, I’ll thin the arugula seedlings to eliminate 1 seedling per hole.  Example: Rockwool # 5 will end up with 5 seedlings per hole.

Ferry Morse seeds planted July 5, 2015

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July 11, 2015. Put arugula seedlings into Tower Garden
1 Plant  per Hole 2 Plants per Hole 3 Plants per Hole 4 Plants per Hole 5 Plants per Hole
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July 19, 2015
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July 25, 2015
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August 1, 2015
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August 12, 2015 – Harvest.  The arugula with 4 and 5 seeds per hole did the best.

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1 1/8 ounce

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1 1/2 ounce

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1 3/4 ounce

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1 3/8 ounce

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1 3/8 ounce