How to tell when seedling soil is too dry?

I used to purchase plastic humidity indicators (they would change color when dry) that I stuck in the seed starting soil to tell me when I needed to rewater.

The last month or so, I have been using a top layer of children’s play sand to indicate when to rewater. To say the “top layer” is probably misleading as the depth of play sand is probably 1/3 of the seed starting containers capacity (the bottom 2/3 is coir).

Henry, are the seed roots in 100% coir and the sand is above the seed? How is that working out? Do you like that better than mixed formulations?

As far as your watering question is concerned, when the seedlings are very young I mainly go by the dryness of the top of the soil and more accurately, the weight of the pot.

However, since my several-month-old seedlings are outside in hot Arizona summer sun, overwatering is less of an issue than for most. I generally fill up the tray the pots are sitting in to about 1/2" of water and within a half hour it’s all absorbed.

This year I stopped using 1-3/4 inch square peat containers for the newly sprouted seeds. Now, when a seed germinates on my 100 % sand in a Petrii dish; it is transferred to a standard seedling tray filled with 72 plastic cells (the cells come in groups of 3 by 3; thus, 8 of these groups fill a standard tray). Each cell is filled 2/3 of the way up with Coir seed starting mix and then the top 1/3 is filled with children’s play sand. The color of the sand makes it easy to tell when watering is needed.

I remove one of the 9 by 9 groups to put the H2O2/ water mixture in the tray (thus, I am watering from the bottom). That group is then put back into the tray.

When I need to transfer the growing seedling to a larger container I use an ordinary household teaspoon to scoop out the seedling plus growing medium. So far this method of transfer does not appear to damage the seedling.

The 3 by 3 plastic groups have another use. They are just the right size to hold the 35 mm film containers that I use when pollinating.