The Best Seed Starting Mix for a Beginner Vegetable Garden
The image above shows two vanilla marigold plants that were sown on the same day, and they shared much of the same experiences up to just before this image was taken. The dramatic difference in the size of the plants is all because I used two different seed starting mixes.
I previously posted about my plans to start a vegetable garden this year. I have planted flower seeds, and a few years ago I had some small basil plants, but I have never grown vegetables before.
Some vegetables can be directly sown outdoors, in the ground or in potting mix, but others can really benefit from a head-start indoors, especially if you live in a more northern climate that has a shorter growing season.
So, I sought to start some plants indoors, mainly cucumber seeds and hot peppers, but also basil and some marigolds. I figure I’ll pick up a tomato plant or two locally, and will sow carrots and dill directly outdoors. Depending on this year goes, I might change things up next year.
What I kept reading online and seeing in videos is that 1) seed starting mix is largely lifeless, and that 2) seedlings don’t need fertilizers or nutrients. I… got things wrong, and learned differently.
I ordered two kinds of seed starting mix online, and they arrived just before my first seed packets arrived. Some ToolGuyd readers seemed interested in this kind of topic, or might be interested in the future. After seeing differences in the first batch of seedlings, I later ordered two more brands to try out.
See? The plants on the right were stunted, even early on, while the ones on the left thrived and grew at a steady pace.
I decided to run a simple experiment, to see which of 4 seed starting mixes yielded the best results.
Seed Starting Mixes
From left to right:
Gardener’s Organic Burpee Organic Jiffy Organic Espoma Organic Gardener’s organic seed starting mix Bio-Blended Compost (composted manures and plant materials), sphagnum peat moss, perlite, mineral and nutrient amendments Burpee organic seed starting mix 95% coconut fiber, perlite, fertilizer (0.06 – 0.03 – 0.03) Jiffy organic seed starting mix 60-70% sphagnum peat moss, vermiculite, coir pith, and lime for pH adjuster Espoma organic seed starting mix 80-90% Canadian sphagnum peat moss, perlite, limestone to adjust pH, and yucca extract Active ingredients: Ectomycorrhizal Fungi, total of 131.38 propagules/cc, Endomycorrhizal Fungi, total of 0.072 propagules/cc
You can also make your own seed starting mix, and there is no shortage of recipes online. However, smaller bags of raw materials are not very economical, and you need to plan on sowing a lot of seedlings to make good use out of a big batch of DIY seed starting mix. This might be a path I explore next year, but for now, I’m happy at the convenience of using premade mix, spending a little more for the convenience.
General Seed Mix Notes
Gardener’s: This starting mix more resembled potting mix, with bits of wood chips, and even a pebble or two. It wasn’t until after I wrote up my first post that I realized it has some composted manures. I probably would have avoided this for indoors use, but there haven’t been any issues yet.
Some of the cells filled with Gardener’s mix grew fuzzy white mold that was easily scraped off. Some of the plants developed green algae on the surfaces due to moisture.
I learned to use less water when sowing my seeds, and things worked out better.
After starting some plants with both Gardener’s organic and Burpee mixes, I preferred the Burpee for its ease of use and faster germination rate, but the Gardener’s won out later.
The Gardener’s organic mix proved to be the best overall. Their non-organic mix is cheaper and said to be finer. I have a bag of that on order but haven’t received it yet.
Generally, you shouldn’t need a whole lot of seedling mix, but cucumbers don’t like their roots to be disturbed and so it’s best to start those in larger pots, and that requires more mix.
Burpee: I liked the Burpee mix for its easier use, It’s supposed to have some plant food mixed in, but it didn’t do much for any of my plants past initial germination. The Burpee mix seemed to allow for faster germination.
It’s hard to comment confidently about germination rates because there are too many factors at play. Maybe one mix was moister? Maybe it was more compressible and allowed for greater seed contact?
Jiffy: The Jiffy mix seems to be a great choice, and will likely be one of my top two picks in the future. It’s a pain to work with though, since it’s fluffy and near bone-dry in the packaging and requires more hydration before use than the other mixes. The Jiffy mix was somewhat spongy, which I did not like.
Espoma: I had high hopes for the Espoma mix, given that the brand is very experienced with plant nutrient amendments and potting mixes. But, the Espoma seems to be performing the worst. The Espoma mix also seemed to be a little more spongier. It was hard for me to find a balance between “moist” and “soggy,” but things might have been better if I moistened the mix and then left it to sit a bit longer.
I read in a couple of places that seed starting mix should (could) be sterilized with boiling water prior to use. I did not do this, but I might give it a try next year to see if it helps with things like fuzzy white mold or algae growth.
Also, I have now started mixing in worm castings with my starting mixes, to give them some organic matter. I’m not sure what else I would be comfortable adding at the start – definitely not compost or other materials typically intended for outdoors use.
I figure that the Gardener’s mix, and its compost and plant materials, is treated during production, and I’ve had no issues with it so far.
The brand of worm castings I found has two grades – standard and premium at a 50% higher cost. I went with the premium product as I read it’s sieved to a finer size, which seems more desirable for indoors and seed mix use. Indeed, it has the consistency of coarse sand. Here it is on Amazon, and I’ll also include a link to it at the end of the post.
You’ll see in a bit why I’m talking about seedling nutrition, because I learned some things I wish I knew one month ago.
Testing and Results
Here’s another image of all four mixes. I loaded (4) 6-cell trays, each with mix that was moistened and then compacted. After the seeds were sown, each cell was placed in a tray filled with shallow water to ensure that the mixes were all fully hydrated. With bottom watering, the water is seeped up through holes in the bottom of the tray.
Some of the mixes, namely the Gardener’s, needs to be sprayed with a little water from above after the seeds sprout, otherwise it seems to form a hard and dry crust.
After this batch of seedlings sprouted and joined my other seedlings under grow lights, I watered them the same and also applied some liquid-soluble seedling fertilizer.
Seedlings do need far lower nutrient levels than larger plants, and so you have to be careful to avoid over-fertilizing them. But they also won’t grow much if you don’t give them any nutrients. I’ll get to that in a bit.
For the experiment, I sowed Sugar Rush Peach hot pepper seeds. These were all sown on 4/18/20, and so the photos taken today reflect seedlings ~20 days old.
Here’s what the seedlings look like today. They all received the same water, and the same fertilizer treatments.
There were two applications of liquid-soluble seedling fertilizer – a little less than 3mL was added to each cell on 4/26 – a few days after they all sprouted, and they were bottom-watered with fertilizer-water mix on 5/2.
That first application of fertilizer was a mistake. I had forgotten that the new sprouts were mixed into my other small seedlings which were supposed to get fertilizer, and so I had already given 3mL to one tray of seedlings before realizing this. So, I gave the same to all of the others as well.
Everything I read about applying liquid fertilizer is meant for top-watering applications. Since I bottom-water, I tried giving a set amount of liquid fertilizer to the plants from the top. I started with 5mL using a syringe, and then went to using a 3mL disposable pipette. Smaller seedlings received a full 3mL, or less if they were really small or alone in the cell, and double that for larger plants.
But, my last fertilization trial, where I bottom-watered with a fertilizer-water mix at the correct proportions, seemed to work out well, and so I’ll likely do this again in the future unless or until I learn otherwise.
This upcoming weekend, the smaller plants will receive seedling fertilizer and the larger ones will receive something a little different. I used a different fertilizer at double seedling strength but half general directions strength last week on a different set of hot pepper plants, and that seems to be a good plan for these.
I had formed fertilizer and nutrient plans for when the plants go outside, but my seedling plans required more response and learning as I go along. I did have the water-soluble seedling fertilizer powder from the start, and probably should have been using it from the start and in greater amounts than my first attempts to fix things. Then again, if I had done that, I wouldn’t have learned much.
In the following images, I’ll be going in a different order than how I described things above. The order here is from best to lowest performance.
Gardener’s Seed Starting Mix Results
So this is one cell’s worth of the seedlings that were sown in the Gardener’s organic mix. It was transplanted into this pot on 5/4, and so it has spent a few days in slightly different conditions than the smaller seedlings.
Here’s a photo of how things looked previously. The seedlings in the Gardener’s mix are at the top of the photo. There is a cell without any germination – either that seed was a dud, or I forgot to sow one there.
Jiffy Seed Starting Mix Results
Here’s a transplanted seedling that was started in Jiffy mix. It was transplanted on 5/6.
These seedlings weren’t quite ready for transplant, but I was concerned they were getting root-bound. I don’t understand why, but all of these hot pepper seedlings would close their leaves a bit during the day, in a V-shaped formation where it almost looked like they were praying. None of my other seedlings did this except towards night time.
The plants were being fed, and they didn’t have signs of under- or over-watering – that I know of – and so I thought I’d see if they improve if transplanted to larger pots.
Here are the 3 remaining seedlings that were sown in Jiffy seed starting mix. Yes, I know that I have scrape the algae growth off the surface. Or, it’ll be covered up and the problem eliminated – I think so at least – when I transplant the seedlings into a bigger pot.
Sorry, in case I confused anyone, any mention of “transplant” in this post refers to my potting-up the seedlings. My mid-sized pots are still delayed (I ordered them 3 weeks ago), and so I had to go directly from seedling cells to 4″ pots. Some smaller seedlings, such as when a larger seedling shares a cell with a much smaller one, have gone into 3″ Jiffy pots – the kind that can be directly transplanted and buried into a larger pot when ready.
Burpee Seed Starting Mix Results
Next, here are the seedlings that were started in Burpee mix.
The Burpee mix saw lots of germinations. I had limited seeds, and so if you see a centered plant, it was the sole seed sown in that space. Here, I think all but one seed successfully germinated, with the dud being in the ~8pm location of the first cell at the top.
These seedlings appear healthy, but they’re growing slower than all the other seedlings.
The Burpee is supposed to have some fertilizer – what’s going on here? On the bright side, the Burpee mix was the easiest to work with, as it required less moisture to hydrate the starting mix out of the bag.
Espoma Seed Starting Mix Results
The Espoma seed starting mix proved to be the worst. I did transplant two seedlings, to see if it would help to get them into a more nutrient-rich mix.
It’s supposed to have “Myco-tone” and plant-beneficial fungi, but what I’m seeing is poor germination success and the slowest growing sprouts.
There is a bright side – the Espoma mix seemed easiest to free loose seedlings from, and so I’d pick this in the future if or when I want to try basic hydroponics techniques. Or rather, I’d be able to use up the remainder of the two bags I bought.
With Respect to Performance:
Gardener’s Organic Mix Jiffy Organic Mix Burpee Organic Mix Espoma organic Mix
With Respect to Ease of Use:
Burpee Organic Mix Gardener’s Organic Mix Jiffy Organic Mix Espoma Organic Mix Additional Examples and Observations
Here’s the image of my vanilla marigolds again. These were sown on 4/8/20.
Ah, so what’s going on here? The cells at the left, which I’ll call 1 and 2, received one application of fertilizer. Cells 3, 4, and 6 all received 2 applications of fertilizer. Cell 5 received 3 applications of fertilizer.
There’s no “nutrient burn,” and you can see the dramatic differences in results.
More nutrients = more growth.
This image was not from today, it was from maybe two weeks ago. Yes, they were all sown on the same day, 4/5/20.
Here’s a more recent image of one of the previously nutrient-deficient basil plants. It’s doing okay. In case you couldn’t tell, the B in the image denotes the Burpee starting mix.
I have not been running strict controls, or taking close notes, but still tried to keep track of things.
Here’s where things get interesting. On the left are basil plants that were started in a coir pot on 4/24/20. These seeds were from a different supplier and could be a slightly different species, I don’t know.
On the right are the basil plants in the Burpee mix that were sown on 4/5/20.
I also have a 6-cell batch of basil seedlings from 4/25 that I mistakenly sown into “transplant” mix. Despite having more organic matter and worm castings, those seedlings haven’t grown quite as big as these.
Basil sown in a mix of Jiffy seedling mix and worm castings on 4/24 have outgrown many of the seedlings grown in Burpee mix on 4/5.
Nutrients can get a seedling or plant back to health and good growth, but it won’t make up for lost time.
With some plants such as tomatoes and hot peppers requiring 6-8 weeks indoors before being planted outdoors, and some hot peppers having length germination periods, timing and steady growth is very important.
I’m kicking myself for not realizing how important seed starting mix and added nutrients can be, but I’m happy I was able to realize there was a different.
To speak candidly, I might not be on the right track yet when it comes to seedling fertilizer and nutrient application rates. But, I hope I’m somewhat close. I’ll be experimenting a bit more as the season progresses, and will hopefully learn a little more that I can put to use in next year’s season-prep efforts.
Here are what some of my jalapeno seedlings looked like in the last week of April.
Some of my plants had yellow leaves, others were turning black. But, none of this was happening to the plants that were sown in the Gardener’s Organic mix.
Were they over-watered? Too little added nutrients?
Adding a couple of mL of mixed fertilizer wasn’t doing much to save these seedlings. Soaking the trays in the mixed solution, basically bottom-watering all the seedlings in the proportionally mixed fertilizer – that definitely seems to have helped.
My petunias, lower left of this image, started off with tiny and dark purple leaves. After seeing fast and successful French marigold and basil germinations in the Burpee mix, I mistakenly declared it to be superior, and so I used it for my only 6 cells of pelleted purple petunias. It is crazy how well adding sufficient nutrients was able to liven them up and fuel growth.
Here, you can see the still-yellow leaves of some of my jalapeno seedlings. While their first leaves (cotyledon) are still yellow, their true leaves are coming in nice and green now.
I think these plants are recovering nicely, don’t you? They’re far too small to be able to grow and strength up for transplanting outside for the season, but maybe I’ll still plant them in the ground either as an experiment or sacrificial easier-access plants in case of hungry animals.
Things looked dire for these seedlings, but they do seem to have bounced back.
Before I write any more, one more thing to mention is that the Gardener’s mix resulted in zero “helmet heads,” a condition that arises when a hot pepper seeding cannot properly separate from its shell, as it’s a denser mix. I saw more “helmet heads” – especially habanero plants, when I didn’t sow them deeply enough. All but two of the helmeted seedlings survived, some needing help to gently coax their first leaves out.
There are a lot of different factors involved with selecting a seed starting mix.
I was worried about fungus gnats, which is why some recommend that starting mix be sterilized prior to use, but don’t seem to have developed any problems. There were 2 or 3 bugs this week, but they could have been fruit flies, I don’t know.
Of these brands, Gardener’s organic mix was the best choice. It provided the best environment for the healthy growth of my plants, which is perhaps the most important characteristic. The Burpee mix was easier to use, and resulted in slightly faster germination, but I didn’t add nutrients fast enough and my plants suffered for it.
Jiffy and Espoma mixes were harder to use. I haven’t calculated the economics of the different mixes, but it definitely seems that you get more per quart with Gardener’s and Burpee mixes than Jiffy and Espoma. The better two mixes were easier to work with, and the other two drier and fluffier, requiring more prep efforts.
For next year, I’ll likely stick with Gardener’s organic mix, and perhaps Jiffy as a close second choice.
I just sowed a second round of cucumber plants in Jiffy mix with worm castings mixed in, and it doesn’t feel heavy enough. With other plants, you can remove the loose mix and the roots will adjust just fine in their new home. However, I keep reading that cucumbers really don’t like their roots disturbed, and that even direct-sowing is preferable if the growing season is long enough.
With Gardener’s mix though, if you have two seedlings in a cell and want to separate them, good luck – you’re going to have a very difficult time of it without traumatizing your plants.
But with the looser mixes – pretty much all the other mixes I tried – it’s possible to separate seedlings for separate transplant.
I’m just going to have to see how things go.
Also, I still have plenty of supplies and could start over with a more scientific approach and added controls and even greater variables, but there has to be a lot of interest for me to do that.
This was my first time trying to grow anything from seed, and I wasn’t aware of how different things can turn out.
The Espoma mix especially disappoints me. It’s advertised as being an enhanced “rich, premium blend of the finest natural ingredients.” That is not what I have seen so far. It seems that their mix used to have earthworm castings in it, but it doesn’t anymore, which could explain why it performed so poorly.
The Burpee mix is supposed to have some fertilizer, but then why did it perform a little worse than the Jiffy mix that has nothing of the sort added?
A lot of this make sense – of course plants need nutrients to grow! My previous container-planting endeavors were with Miraco-Gro, and all I needed to add were flower seeds, water, and protection against animals who liked to decimate anything that tried to grow.
I hope you found this post to be helpful – please let me know. I threw a lot of information and details at you here, and if there’s interest I’ll tighten up the sections and republish a more formal write-up.
I wish I could send a link to this post to a one-month-younger me, but I can’t. Hopefully this will save some of you from making the same mistakes I did.
Supplies I Used Seed Starting Mixes Gardener’s Organic Burpee Organic Jiffy Organic Espoma Organic Fertilizers and Nutrients VermisTerra Premium Earthworm Castings Fox Farms Grow Big Liquid Plant Food Gardener’s Seedling Fertilizer Other Seed-Starting Supplies 1020 trays, humidity dome, 6-cell trays: via Bootstrap Farmer, via Bootstrap Farmer on Amazon Feit LED grow light GE LED grow light – I like this one better TP-Link Kasa Smart Plug (for grow light timer functionality) Rubbermaid utility tray (so that I don’t make too much of a mess in the kitchen when sowing seeds) Hydrofarm seedling heat mat Hydrofarm Jump Start heat mat thermostat GE power strip Wire shelving – I use a larger rack I already have, but smaller ones could work too Rubbermaid 6 quart Container – I use smaller containers for smaller mixes, and the 6 quart has been great for larger quantities
I ordered all of the seed-starting supplies from Amazon, except the Bootstrap Farmer supplies, which I ordered from their website directly.
Please keep in mind that I’m still learning about all this, but don’t hesitate to ask if you think there’s something I can help you with.
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