Starting Seeds Under Grow Lights

The mortality rate of seeds that I plant directly into the garden is high. I blame it on the arid climate, because it is difficult to keep the soil moist for the time it takes to get the seeds well-sprouted.  The solution is to start seeds inside in soil blocks and plant them out when they have a couple of good leaves and some roots.

LED grow lights are fabulous for this. They are low-power and don't produce much heat so they don't cook the plants.


Don't let articles about basements full of reflectors and lights scare you off. There is a difference between growing plants all the way to flowering and fruiting and just getting seedlings started.  My setup won't get tomatoes from seed to harvest.  It will get them from seeds to seedlings and do it inexpensively.

This was the first "OMG, I need LIGHT, and I need it NOW" setup.  Two inexpensive grow lights are dangling from some steel tubing over my workbench. They have a timer set to provide about 14 hours of high intensity light every day.

Temporary Grow Light Area

You can see the mini greenhouses of salvaged transparent pastry and salad green boxes labelled with painters tape and permanent marker pens. The seedlings are in the boxes, protected from drying out.

The next version will have two more lights and more space, but will not be any fancier.  
WARNING and update: The air inside the plastic boxes CAN reach temperatures too high for successful seed germination.  I did not have problems when the workshop was a chilly 55 degrees, so I assumed that the set-up was working.  Later I started having entire boxes fail to germinate.  I was puzzled, then realized that I was not monitoring the temperature inside the boxes.  It was NINETY-TWO degrees in the box I measured.  That explains it.

I need to figure out how to keep the soil blocks moist and the temperature down.  There will be an update.

Why I don't use a sunny window

Sunny windows are for cats, not seedlings.

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Starting Seeds in Soil Blocks: Part 3, After They Sprout

They sprouted!  Now what? 

Unless you want the seedlings to die from lack of space for their roots, you have to do something with them.  You have three choices:

• Direct planting out to your garden
• Moving the sprouts to a larger soil block to grow larger
• Moving the sprouts to a pot, either permanently or to grow larger

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Starting Seeds in Soil Blocks Part 2, Making and Planting the Blocks

Collect your trays for the soil blocks.  I use salvaged  clear plastic containers that salad greens or pastries are sold in. I also use small freezer containers to hold a 20-block set of seeds.  If you will be making large quantities of blocks, cafeteria style trays or nursery trays would be convenient if you have some way to retain moisture in the blocks.

You will also need a sturdy trowel, a drywall mudding blade, and a pair of tongs with flat 1-inch tips.

The tools: drywall knife, mason's trowel and salad tongs

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Starting Seeds in Soil Blocks Part 1, Making the Mix

Soil blocks - just a cube of compressed dirt - have advantages for gardeners who grow their vegetables and flowers from seed.

40 lettuce seedlings in 3/4" soil blocks
in a scavenged plastic deli tray

There is no plastic except for the reusable, perhaps scavenged, trays for the blocks.  The micro blocks shown here take a very small amount of space compared to other seed starting methods. If a seed fails to sprout, the block can be tossed into the garden or compost bin. When well-sprouted, after a couple of true leaves have developed, the seedlings are ready for planting out or moving into a larger soil block or a pot.
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Using a Seed Starting Heating Pad

Many seeds require a warmer soil temperature for germination than the seedling needs to grow after germination.  This ensures that the seeds germinate when the weather is warm enough for the plants to survive.

Frost on my lettuce seedlings.

For most seeds, directly planting the seeds in the garden is the preferred method, but many gardeners start some of their plants indoors with "bottom heat" to provoke germination and get an early start on the season.

• They want to harvest as soon as possible, whether for market stalls or just bragging rights.
• Their growing season is too short for this plant.
• By the time the soil is warm enough, the remaining growing season is too short to get any harvest.
• Their soil never warms up enough to germinate the seeds, but transplants will grow.
• Their area for starting seeds indoors is too cool for germinating.
• They need to get the plants germinated and seedlings established before hot weather arrives.
• They want to get their garden work done before hot weather arrives.

I'm gardening in several of those categories, especially the last two.  I want to get the chili peppers and tomatoes in the ground to avoid the coming hot weather, and my workshop is too cool.
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