Soil Blocking Trial and Error

An area of gardening that has never been my strong suit is starting seeds indoors. When I had access to a header house, greenhouse, germination station and all the best tools in college I started thousands of basil plants with one of my friends. We would come in before class and seed another tray, separate sprouted plants into their own pots and maintain our previously started basil until it was ready to sell in the college’s weekly greenhouse sales. Since then I haven’t had such luck. Last year I saw a video about soil blockers. No need for brittle plastic pots, no root binding, more seeds per tray - sounded like a win, win, win to me. I made the investment to buy a one and a half by one and a half inch blocker that made five blocks at a time. I got some cafeteria trays to keep them on and was thrilled thinking about how many hundreds of plants I would be able to fit under my few grow lights. 

1.5 x 1.5 Inch Soil Blocker

Perhaps I take the 4-H motto of ‘learn to do by doing’ a little too far sometimes but I tend to see one or two videos about something and think that I can figure it out from there, I don’t need to research it, right? Well, the first year of soil blocking was a flop. I packed each block so full of soil that while I did make sturdy blocks that could hold up when tossed from hand to hand I forgot that most seeds, especially ones you really hope thrive, don’t like to start their lives trying to send down roots into bricks. So, while my germination rate was decent nearly all of my plants stunted at less than 2 inches tall. Even when I planted them out in the garden they refused to grow all summer. Okay, so don’t pack the soil too tight.

Last year's soil blocks

This year I tried again. I mean, I did spend a pretty penny on this blocking contraption and I still thought it made a lot of sense in theory. Careful not to overpack the blocker I punched out a tray of soil blocks and planted my seeds. At the same time I filled some plastic pots and planted some of the same seeds in them, namely tomatoes. Eureka! I had germination. Things were looking good, until they weren't. My starts, the tomatoes in particular, stayed in the cotyledon stage for three plus weeks, in both the soil blocks and the plastic pots. I finally fertilized them and breathed a sigh of relief when I saw the true leaves begin to emerge. At the beginning the tomatoes grew at the same rate, although the soil block ones seemed to germinate a day or two faster. 

The tomatoes finally have true leaves!

Soil is not packed as tight as last year

The next lesson I learned is that the soil blocker size that I have is great for starting seeds but you can’t let them grow as long as if they were in a 4 inch pot. Soon, my potted tomatoes were twice the height of my blocked ones. It was time to pot everything up. For my tall tomatoes I removed the lower leaves and planted them deep into tall pots with the soil coming a lot of the way up the stem. This helps to stabilize the plant because when the tomato stem is buried in soil it will grow roots all along it. That is why tomatoes are a plant that I recommend newbies try starting indoors because even if they get tall and gangly that doesn’t mean they have to stay that way. This rule unfortunately does not apply to all plants though so you might have to experiment if you have a lot of leggy plants. Plants in the nightshade family - like tomatoes and eggplant, or those in the squash family are good ones to try this technique on. 

Tomato started in plastic pot vs. started in soil block

Now, as the days are getting warmer, I am hardening off my tomato plants. This is another area that I have struggled with in the past. I think oh these poor, gangly plants could really use some sunlight so I stick them outside in a sunny area and then forget about them. Soon they are fried and I am stuck with either very sad or very dead plants. This year I have been putting them in the shade for one to three hours a day to start with. Today the wind kind of knocked some stems over but that will help strengthen them in the long run. Perhaps next spring I will invest in a fan to help prepare my starts for the endless wind we experience on the prairies. So far I have not cooked my tomato plants, hopefully I am finally getting a hang of this hardening off thing. Lord willing I’ll be posting my abundant tomato harvest soon enough. 

The Sweet Million Tomatoes (top six) grew MUCH BETTER than the Rutgers (bottom two)