Seed starting mix results

Context:  Observations from my manure bioassay led me to question the efficacy of my usual seed starting mix.

3 wk germ test
6 cells of each medium.  Results after 3 weeks.

Setup: Basically I grew lettuce and peas in different media to see which worked best.  The media were:  100% peat moss, 100% purchased potting mix, 100% vermicompost, 50% peat 50% vermicompost, and 50% potting mix 50% vermicompost (my usual mix). Full description here.

Materials used:  Peat moss, Miracle Gro potting mix, vermicompost, lettuce and pea seeds.

I wanted to test the materials that I usually use and have on hand.  It has been documented that using only 10% vermicompost is plently for most plants.  My percentages are much higher because for me, vermicompost is a free material that I make — I try to be as sustainable as I can so if I don’t have to buy stuff for the garden, great.  My bias would be to use 100% vermicompost.  Using higher percentages of vermicompost does not hurt plants or seedlings but does not seem to increase yield either. Others advocate using 100% vermicompost to produce the best seedlings.  I’ve had trouble using 100% vermicompost so I usually mix it with another material.  I also realize that some people are reluctant to use peat materials. I rely on Sara Williams‘ judgement.  Canadian peat moss is a sustainable industry.  It constitutes 25% of the world’s peat lands; peat regrows after 20 years; only 0.03% of Canadian peat is harvested each year; the amount of peat moss harvested from Canadian peatlands every year is nearly 60 times less than the total annual accumulation of new peat moss.  (source: The Canadian Sphagnum Peat Moss Association) For me, peat is more economical and uses less fossil fuel for harvest, manufacture, and transportation than the oft mentioned alternative: coir.  We’re far away from tropical beaches where the coconuts grow.

Results:  Only one cell didn’t germinate:  one pea plant in 100% peat moss.   Other observations:  lettuce grew better with peat moss (both 100% peat and the 50/50 vermicompost mix); peas grew better in 100% potting soil.   Lettuce did NOT like the potting soil or the vermicompost.

100 peat
100% peat moss.
100 potting
100% consumer potting mix
100 vermi
100% vermicompost
50 peat 50 vermi
50% peat moss, 50% vermicompost
50 potting 50 vermi
50% potting soil, 50% vermicompost (my usual mix)

Looking at overall germination and robustness of seedlings, it appears that 50% peat moss and 50% vermicompost is the winning combination in this limited test.  I will use this combination as my seedling mix this coming gardening season.  Caveat:  this is hardly a scientific experiment and definitely not definitive.  It was interesting, and for me, something new to try.  I hope you all try out some citizen science to see what works for you with your setup and resources.




Seed starting mix experiment.

One inadvertent result of my manure bioassay was noticing that germination was quite poor in the control medium. I usually start my seeds in a 50/50 mix of purchased potting mix and vermicompost. This mix is what I compared the manure to. Lo and behold, the seeds germinated better in the manure. Hmmmm. 🤔

After observing the difference in germination between the garden manure and my standard mix, I thought I had better test a some different combinations. I may need a different seed starter!

Testing setup

My control medium is 100% peat moss. I chose it because it is sterile, has no nutritional benefits, and is considered soiless (plus I had some!) The testing media are 100% potting mix, 100% vermicompost, 50/50 peat and vermicompost, and 50/50 potting soil and vermicompost (my usual mix).

Mom gave me a multi seedling container while she was cleaning out. Little did she (or I) know it is ideal for this test! I chose to try lettuce and peas for germination since they both had similar germinating times and temperature (plus I had some!)

Germination tray and setup.

Each mix got 6 cells of the tray * 5 mixes = 30 cells total. For each mix 3 cells were planted with lettuce (2 seeds) and 3 cells were planted with snap peas (1 seed). All lettuce was covered with vermiculite. All peas were planted 1 inch deep. They were watered in, the cover attached, and then popped under the grow lights (mainly for warmth).

I will provide an update after a week. I’m curious to know with what seedling mix you’ve found most success.

Manure bioassay results.

My 2018 potatoes were slow to emerge and grew with stunted, curled foliage.  They were planted in purchased manure so I suspected aminopyralid contamination.

Certain herbicides can linger even after passing through the digestive tracts of ruminants and can affect sensitive plants like tomatoes.  Time and the biological actions of soil inhabitants will eventually dissipate the harmful effects of these herbicides, but meanwhile I have to plan my garden for 2019.

To assess what will grow in the beds where I spread the manure I conducted a bioassay for seedling germination and leaf curl.  I did not test any sensitive plants like tomatoes since I will be growing those elsewhere.  I tested the seeds of plants that I wanted to grow in these beds.

After 3 weeks under indoor lights, I recorded the final results of how many seeds germinated in the manure versus the control (potting soil and vermicompost) and compared the seedlings for any signs of leaf curl or stunting.

Comparing seedlings.

Long story slightly shorter, I plan to go ahead and plant brassicas, beets, and carrots in the beds since they did not seem to suffer any ill effects.  Whether that carries through to harvest will remain to be seen.  Squash will also be planted out in these beds since they loved the manure last year and I suspect will do fine once again this year.  My potatoes will be planted in buckets and will hopefully produce a decent yield next year.  The other change will be to be much more careful with any products I bring in to supplement the garden soil.  I will be paying more attention to producing my own compost next year too.

Happy garden planning to you.

Manure Bioassay Germination

After problems with potato germination growing in a load of puchased manure last spring, I suspected aminopyralid contamination. I’m conducting a “citizen science” bioassay for germination and leaf curl problems to see what I can plant in these beds come the spring.

Trialling seeds.
Brassica trial seeds.

After 10 days, germination looks promising (control cells on the right). All seeds planted in the manure have germinated except some of the carrot seeds which may need more time.

Bioassay germination.

I will continue to let these seedlings grow out to see if the carrots germinate and to see if there is any leaf curl. I’m already noticing some leaf differences in the cucurbits. The cucumber seedlings in the manure pots seem more shriveled than the control plants. (See top left pot.) Stay tuned for more results.

One interesting observation is that germination rates are actually higher in the manure than in the vermicompost/potting soil! I’m trying not to put too much stock in this since the sizes of containers are different. My methods would not stand the rigors of a science lab, but my goals are different. Foremost of which is I want to find out what will grow in this soil. The brassicas seem to be doing just fine so I can add them in to the 2019 garden plan.

These preliminary results do raise questions about the efficacy of my seeding medium. I’m devising a different experiment that would test germination rates of different mediums. Do you have any suggestions on seeding blends to try?

Manure bioassay setup.

I purchased a truckload of composted manure from a local farmer in the spring of 2018. When I planted the potatoes into it, the plants came up slowly, were stunted, and had curled, misshapen leaves. After researching online, I suspected that the manure was contaminated with some kind of aminopyralid.

Luckily the squash grew decently and I salvaged what I could of the potatoes.

In order to plan my garden in 2019, I need to know if the contamination is still present and which plants are affected and how significantly. The contamination eventually wears away but some sensitive plants will suffer for years.

To detemine the level of contamination, Washington State University recommends conducting a bioassay. The details of which can be found here. Basically you grow your plants in the wonky soil and compare against a neutral control to assess the effects on germination and for leaf curl.

Garden soil samples.

I am testing seven places in the garden against a control of my standard potting mix. I have planted beets, carrots, cucumber, and pea seeds in 6 pots of manure from 6 different garden locations, and have planted the same seeds in 4 pots of potting soil and vermicompost mix.

Brassica trial. (Control cells behind)

I’m running a concurrent test just for brassicas (cabbage, collards, kohlrabi, and tatsoi) to see if they’ll grow in a bed I would like to reserve just for them. Again these seeds will be measured against 2 control pots.

Awaiting results.

Right now they’re under my grow lights in the basement. As my mother says, “We shall see.”

5 Favourite Gardening Tools. Part V.

Super Scoot!

I am of the age where my body and my brain are at odds with each other.  (Although now that I think of school gym classes, this may not be a recent phenomenon.)  At any rate, bending, stooping, and straining seem to be more of an issue these days.  The clincher was one day when I was sitting in the garden pathway doing some task and ants got in my pants (literally) and I wound up with itchy ant bites all up my legs.  Nothing like discomfort to spur one to action!

After scouting the internet for garden scooters to keep me off the ground and out of the ants, I settled on this model:  the Step 2 Garden Hopper!  Note:  it does not hop.

The height is what sold me on this particular garden scooter.  Other models were simply too high.  I’m not *that* short, but bending over from on far didn’t seem like a great solution.  The other feature that I really appreciate is the generous holding capacity of the lower level.  I can throw my tools, seed packets, garden tags etc. in the bottom and then put the whole thing back in the shed when I’m done.  This reduces (but not eliminates) lost tools in the garden.  I’m also quite pleased with the way it goes over terrain.  Sometimes it does roll away on the slightly slanted sidewalk which one MUST be cognizant of before sitting down (ahem).  But, all in all, this is a comfort, it extends my pleasure of working in the garden, and it works very well !

Do you scoot in your garden?



5 Favourite Gardening Tools. Part IV.

My well-used hori-hori knife.

The hori-hori was gifted to me some years back by my partner who had researched great gardener gifts.  Major points won. ❤️👍

My partner also doesn’t remember the name of the tool and refers to it at various times as the “huki buki,” the “oogie boogie,” and other variations. 😂

It is a Japanese digging tool with a serrated edge on one side and a cutting edge on the other, both coming to a point.  The word ‘hori’ means ‘dig’ in Japanese and the word ‘hori-hori’ is an onamatopeia for the digging sound.  (With my clay soil, my digging sounds are more like “thud, grunt,” but I think the marketing team would have vetoed that.)

I use this handheld tool pretty much every gardening outing for weeding, opening compost bags, cutting tree roots (the small ones) and cabbage stems (the big ones) and anything that might need prying out of the soil (small rocks, stubborn parsnips, etc.)

Both Imperial and metric measures!

I also love it for transplanting.  Its sharpness make a quick hole and the edges can slice through root bound plugs.  The model I have is ruled which is helpful for spacings and depths.

Do you have a hori-hori?  Or is it now on your X-mas list? 🎁