Peat-free Experiment

UPDATED March 10, 2023

Peat, the great 21st century garden debate and efficient and vast carbon sink, is a perfect ingredient for starting seeds. It’s light and fluffy, a friendly medium for very tender and delicate emerging roots. But in this time of environmental crisis, one that I learned was already here in college in the 90s, it’s hard to accept that removing a functioning carbon sink is a good idea, even and especially as people who garden.

Does my other carbon sinking offset my usage? I mean, I guess maybe. We are actively converting our other grassy lawn into carbon-sinking native prairies. We’ve added dozens of trees and shrubs to our property too. But my demand for peat is part of a collective demand, which impacts the supply. And thus, why I do really hope that once we finish the large bag I bought last year, I will have a better alternative going forward.

Peat-free above, and peat-ful below. It’s a clear loser for tomatoes, but less clear for some of the other seeds I sowed.

Years ago I did try making soil blocks with coconut coir. My recipe is still one of my most-watched You Tube videos and also something that gets traffic on my public garden resource library. I didn’t like how most plants grew with coconut coir; the one exception is I did use the block mixed half and half with compost for growing ginger.

So I thought maybe what if I try to completely remove that fluffy ingredient and replace it with coarse materials that also allow for pore space, those spaces through which the tender roots will reach and grow. And that’s where I started with this winter’s trials.

Peat Free Recipe #1

This recipe was truly free of peat and anything like it. I mixed 3 parts compost with 2 parts perlite and 1 part coarse sand. It was immediately heavier than my peat soil blocks, both in the real weight of it (sand weighs a lot more than peat) and in its texture. I was immediately skeptical.

The Traditional Recipe

A few days later, I mixed up my traditional recipe, which can be found in my book and also here. This recipe is roughly 3 parts peat to 2 parts compost and 2 parts perlite. If you have a bucket of “garden soil” you can add that too, which is what Eliot Coleman calls for in the OG recipe, but I’ve always bought “garden soil” and in all honesty it’s like adding another part of peat because it’s a peat-based soil mixture. It’s a little heavier and ideally, if actual garden soil, would contain some clay and smaller particles that will help give them structure.

The Experiment: Phase 1

I sowed the same Botanical Interests seeds in both trays: Sweetie tomato, Beefsteak, Nero Toscano kale, Sweet Alyssum, and Ventura celery from Adaptive Seeds (I think). The Peat free ones were planted on January 15 and the Peat-ful ones on January 17.

Results (as of Feb. 9)

I had rather lofty hopes that this would be a panacea. It was based on some peat-free recipes I’ve read about in recent years, so I wasn’t entirely making this up. But, it was far from it.

I’ve always used really light potting soil medium for seed starting, and had never have faced poor germination in my 25 years of growing. So I quickly concluded that in addition to heat mats and lights, the soil blend is probably another big unknown when folks ask me why their plants aren’t growing well. I usually ask them about lights, watering, and heat mats but don’t really consider the soil. But I can clearly see. that if their tomatoes germinated a month ago and look nothing like mine, the soil could very well be the culprit.

Peat free on the left. Everything about that plant from the way the stem bends and how thin it is to the smaller and fewer true leaves tells me this soil is not as welcoming as my trusty peat moss soil block recipe.

Sometimes doing these things even though we know so much already brings new knowledge and understanding into our lives. I love experiments like this. Being a perennial student is why I garden with such passion and determination.

Soil that is too heavy is a rather unwelcome home for those tender roots I’d mentioned above. And, unfortuntately, this mixture is not a good fit for tomatoes at all, and it’s also not great for the alyssum.

But it wasn’t a complete failure. The kale and celery both seem to be growing at similar rates. And this is both fascinating and curious. Celery seedlings are miniscule! Smaller than the Sweet alyssum. And what’s also strange is that the Sweetie tomatoes germinated a bit slower but then sort of stopped growing, while the Beefsteak just didn’t even break ground at all, except for a few that are stuck in just germinated land.

Phase 2: PittMoss vs Coco Loco + Cowsmo

Now that I know the compost/sand/perlite mixture is too heavy for germinating tomatoes, I won’t be using that mixture for seed starting, and needed to research other methods. PittMoss is a recycled paper product and OMRI (organic) certified. I used it as a 1:1 replacement for peat moss. (3 parts PittMoss, 2 parts perlie, 2 parts Cowsmo compost)

Coco Loco is something I’ve been hearing about recently, both from MGG members and from an IG friend I met up with in Seattle. It is suppose to be triple washed, has some perlite in it, and bat guano for nutrition. I mixed 2 parts CocoLoco to 1 part Cowsmo compost for those soil blocks.

Both sets when really well hydrated (with a little standing water in the bin) formed soil blocks just as well as the peat, which is important for viability. I am hoping, since I’ve invested in both these bags, that the results will be similar and I can use them each for the remainder of the growing season.

I sowed the same Botanical Interests seeds in both trays: Sweetie tomato, Beefsteak, Nero Toscano kale, Sweet Alyssum, and Ventura celery from Adaptive Seeds (I think). Both trays were seeded in February 28.

The sweet alyssum and kale has already started germinating. The tomatoes and celery will take a little longer, but I’m sort of banking on better celery germination since the celery in my pepper tray was so dismal.

What happened to those first two trays? I did pot some of the celery and alyssum up, and they are growing great under the lights. I harvested the kale and will make a yummy kale salad for us this weekend. I composted all the tomatoes, as I don’t grow Sweetie anymore and I prefer Whittemore beefsteak above others we’ve grown.

I kept the celery and some sweet alyssum from the first two trays, and will hopefully have extra early celery this spring thanks to these experiments.

Phase 2 Results

I was honestly not expecting such stark differences in germination, but it’s clear 11 days in that the Coco Loco is a superior product compared to the PittMoss.

I’ve had slow or no germination in the PittMoss, and the seedlings have largely stalled, especially the tomatoes. The alyssum is equally unhappy in the PittMoss and the kale is shorter and less vigorous too.

Coco Loco & Cowsmo on the left versus PittMoss (1:1 replacement for peat in my traditional soil block recipe).

Just like the first experiment, these are under the same light, with the same kind of heat mat, and have received the same type of watering — as well as been sowed with the same packet of seeds (even as the first set of test trays, peat vs compost, perlite, and coarse sand).

If I were forced to rank the best peat-free soils, it would be Coco Loco or the heavy compost/perlite/sand mixture in top spot and then honestly the peat recipe would be runner up.

As I’ve been pondering this more, with our heavy 2” of compost on top of our beds each fall, we germinate all of our direct-seeded crops pretty much right into 100% compost. Makes me wonder what that would look like. I might try that during our June sowing trays for the fall garden, but for now I know that the Coco Loco is a great alternative to peat. I will keep the Coco Loco tray several more weeks, and may even keep the tomatoes to give away to community and donation gardens this spring.

We do have quite a bit of peat left, so I will continue to use it up this year, and then can confidently transition away from it once and for all.