1.5” vs 2” soil blocks
We invested in a second soil block size this winter, because I wanted to use it for sowing flowers instead of my larger capacity 128-plug trays that always end up with extremely root bound seedlings that become extremely thirsty little things.
Turns out smaller soil blocks are just as challenging as the 128-plug tray at keeping things from drying out. I think part of the reason is that unlike the 2” blocker which I can get pretty much tight in a seed block tray (at 5 rows of 10), there is always a gap for the 1.5” blocks and thus more opportunity for water to evaporate and desiccate quicker.
I lost several fennel seedlings due to drying out. Those 1.5” soil blocks are unforgiving relative to the 2” blocks. Learning as I grow, it’s the best part even and especially when it comes with hard won lessons such as this. Now that I know this and only lost a few fennel, I am much more vigilant with checking those daily for water levels and dryness and I’m even watering those from above as often as refreshing the bottom watering tray.
The other phenomenon that sometimes happens with my soil block trays is the middle dries out faster, as seen here with this gap.
I am learning that each size has value. I will continue to use this smaller blocker for flowers, which I already crammed into even smaller pots in years past. This includes flower that establish quickly such as calendula, sweet alyssum, marigolds, cosmos, and zinnia. I will also continue to use the smaller blocker for beets and lettuce, things that I just like to give a brief head start to and then into the garden they go.
The 2” blocker has a lot of advantages and we really thought long and hard when we researched these back in 2017 before investing in one as to which size to purchase. At $40, we delayed this purchase for many seasons, especially when we had a tiny urban garden because the cost seemed excessive. And, we wanted to invest in just one universal size. And it really is an amazing and utilitarian size — the only downside is that you can only have 100 seedlings under our lights.
128-plug tray means more babysitting once their roots establish.
But as I thought about reducing plastic consumption and the downsides of those 128-plug trays drying out so fast during the hardening off process, it made me so curious to see the difference in plant vigor if I gave them a little more room. So I invested in the smaller blocker last month. It’s actually a significant decrease in the number of plants I can sow per tray, but I think the quality of the plants (78 blocks vs 128 plug tray) is worth the added space.
If I were to sell tomato seedlings, I bet I would use this 1.5” blocker to start 78 seedlings and then pot up quicker into 3.25” pots (in 3 weeks instead of 4-5 weeks in the 2” soil block I currently use). Or in the summer if I wanted to have a fall plant sale, same thing — it would be a fast way to get a lot of plants going. But this begs the question: how many of us need to start 78 plants for our garden? I’ll share more on the topic of how to plan for what to start in each tray next.
If you are thinking about invested in a soil blocker and have a smaller garden, I would recommend the 2” soil blocker over the 1.5” blocker — but 72-plug trays are also awesome resources and what we used for our first 16 years of gardening on smaller plots of land.
