Seed Starting Systems: Peat Pots to Soil Blocks

Soil blocks with Early Jersey Wakefield Cabbage starts, up in three days.

I yearn for a greenhouse, but for now, I start my seeds indoors on shelves under lights. Over the years, I’ve tried numerous systems for starting seeds. Not that any of them were particularly bad, and all produced seedlings in spite of my habit of over watering, but I’m still fiddling around with what works best for me.

Here’s my basic seed starting setup:

• I have a two-tier wooden shelf (built by K with 2x2 scrap wood), with lights on chains above each level so they can be adjusted as plants grow. When I’m done with seed starting for the year, I can take the shelves apart to store, or I can leave them as is and set the whole thing next to my potting bench. I’ll use it throughout the summer to store supplies and hang herbs or dry garlic and onions.

• A timer turns lights on at 6 a.m., and off at 8 p.m.

• I use a heat mat on one shelf, then, once seeds germinate, I move the trays down to the shelf that isn’t heated.

• As seedlings start to get taller, I hang a regular window fan at the end of the shelf and give them a bit of a breeze – helps prevent damping off and it really seems to make my seedlings stronger.

Far right, cole crops off heat mat, nearest camera, peppers still under plastic

• I lay a heavy gauge plastic across the tops of the trays until the majority of seeds have germinated. Once I see sprouts, I remove the plastic.

• Sitting next to my shelves are jugs full of rainwater, plus this sprayer (also filled with rainwater). I prefer using rainwater to tap water, as I’m on city water with chlorine so strong I can smell it sometimes. We do filter our water, but I really would rather melt snow, and catch gutter runoff late in winter.

• I start the hardening off process inside with the open window and fan before I put them outside.

These are some of the different systems I’ve tried:

Potting soil in flats with rows of seedlings, which I prick out and pot up into 2x2 pots.

• PROs: I can start a lot of seedlings in a small space. I was also able to repurpose some of the clamshell containers that lettuce from the grocery store comes in, and they were perfect little greenhouses. I still like to use them for lettuce, bunch onions, some flowers, and greens.

• CONs: I wasn’t able to bottom water, and I had way more seedlings than I had space for once they were potted up. They seemed a bit more gangly and fragile, and thinning is necessary.  

Potting soil in 2x2 pots plastic pots set inside trays

• PROs: This is probably the system I fall back on more often than not. I’ve had relatively good luck by setting them in a solid-bottom tray and bottom-watering them. Seeding into these pots from the beginning, I found that they had enough room to get seedlings all the way to transplanting time, so I spent less time potting up.

• CONs: The pots don’t last too well beyond a year or two and require cleaning and storage. 

K-cups in trays (lights still to be hung up)

Potting soil in Repurposed k-cups

• PROs: Repurposing k-cups from our office break room was a good way to use something that is not eco-conscious. I saved the coffee to dump in my compost bin and made the teeny hole at the bottom bigger for better drainage.

• CONs: They still ended up in the landfill eventually and were quite small—which required potting up. They just didn’t work as well as I’d hoped, but could work well for starting some seedlings. 

Peat pellets inside trays, and peat pots

• PROs: Again, no real waste. Simple. No root disturbance when planting. Peat pots worked pretty well for some of the short-time seedlings. Plants like pepper and tomatoes that start 8 weeks ahead of planting were OK but the pots were breaking down well before I was ready to plant. For seedlings that only need a couple of weeks before planting, they would work better.

• CONs: Not wild about using peat from a sustainability standpoint, and they got mossy and soggy. My seedlings just didn’t thrive in them. Could have benefited from some compost tea for nutrition, and a mist with chamomile tea (it’s an antifungal) would have helped. I don’t like using straight peat as a growing medium. I prefer coir as a replacement.

Styrofoam cells inside trays

• PROs: Lots of cells so that I was able to get a lot of seeds started, and less root disturbance than when sowing flats. I really liked these speedling trays from Peaceful Valley. Easy to clean and reuse. I still use these, and I like how they create “plugs.” No real problems with bottom watering, and my seedlings did well.

• CONs: It's a pretty big tray, and I couldn't move seedlings according to water, light, and temperature needs. I also spent more time potting up into 2x2 pots, so I went back to the 2x2 pots. (It's not that I have anything against potting up... just seems like an extra step at times.)

Soil Blocks inside trays with wicking liners

Tomato seedlings in soil blocks

• PROs: Zero waste, economical, easy to plant, and I had good luck with germination. I use the 2x2 blockers rather than starting with the minis and making more blocks. There is also something satisfying about squishing the soil blockers into the mix and creating perfect little blocks. Kind of like playing in a sandbox. Which is germane to nothing, but it pleases my inner child and my late winter need to stick my hands in something like soil.

• CONs: I had a lot of issues with moss growing on top of the block. I was overwatering, mostly because the wicking material made me uneasy. And I wasn’t using a fan at the time, which might have helped circulate air. I also didn’t like the flimsy trays I had them set in. 

SO… this year… I'm using soil blocks set in these 1010 Seed Starting trays.

• I love these trays (I swear, no one paid me to say that. But I do like them. Seeing them stacked up and ready to go on my shelf makes me happy). They’re sturdy and will last far longer than the basic lightweight trays I’ve gotten at the garden store in the past. I bought trays with holes and those with the solid bottoms, and they nest nicely and solidly. Perfect for bottom watering. The smaller size (10x10) makes it easier to move the trays around if needed and is just easier to manage for the smaller volume. I like to group my seeds and trays by what’s growing. So, I can put seeds like peppers in a tray that will sit on the heat mat, and some bunch onion, kale and cabbage in another tray that won’t appreciate so much bottom heat. With the bigger trays, I can't always customize watering and location as much as I like for the specific seedlings. I’ll be curious to see how they work with soil blocks.

• I also added some vermicompost and vermiculite to the seed starting mix this year. It is a peat mix for now. (I have a big coir block to use, but we’ve had a cold, snowy spring here.  Until it warms up a bit outside – enough to drag the hose out and hydrate the pressed coir – I’m using peat as a base.)

• In addition to the soil blockers, I’ve been saving plastic clam shell containers from the grocery store for some seeds, and will use them as flats.

• I'm also starting seeds a bit later -- I think I've started too early in the past, and seedlings were ready to set out before the outside soil and temps were warmed up. As a result, they were a bit stressed by the time I put them out. I'm always a bit impatient... so I'm working on not hurrying my plants into the ground this year.

And so, Seed Starting Experiment 2019 begins… stay tuned.