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Container Gardening

need help with seed starting mix!

kawaiineko_gardener

9 years ago

I want to make my own seed starting mix. The thing I'm confused about is how much of each ingredient to use for the size of the batch I want to make. I plan to make a 15 gallon batch.....the mix says to use.....

2 parts sphagnum peat moss OR coconut coir – for moisture retention
2 parts finely sifted finished compost, vermicompost or a blend – for nutrients
1 part perlite – for drainage and to reduce weight
1 part vermiculite – for drainage, moisture retention and to reduce weight

I really suck with ratios, so if I'm making a 15 gallon batch what would each of these ingredients translate to with gallons?

Also, it says to add 1/4 cup of slow release fertilizer for each cubic foot of mix.

How many cubic feet would be in 15 gallons of the mix? When converting from the 15 gallons to cubic feet, should I just convert to dry cubic feet?

Also one question about the fertilizer; it says to use a balanced slow release fertilizer (one with equal parts each of nitrogen, phosphorus and potassium). I found a bag of slow release fertilizer that is 5-5-5. It doesn't specify whether it can be stirred directly into the soil mix. However since it's slow release, I'm going to assume it would be suitable for container gardening? Yes or no? I honestly don't know.

Featured Answer

gardengal48 (PNW Z8/9)

9 years ago

If one reads the "hundreds of reports" - or a representative sample, as hundreds do not turn up if you search under those terms - one will discover that the ability to control damping off diseases with compost is irregular at best. Even the Cornell study - which addressed only the control of Pythium with vermicompost (not homemade or purchased yard waste compost) added this caveat: "However, it is important to note that composts suppressive to a single pathogen are often conducive to other pathogens (Bonanomi, Antignani et al. 2010), so there is no guarantee that these materials will suppress disease caused by other soil borne fungal or oomycete pathogens."

And while compost is well known for its disease suppressing abilities in garden soil, the use of it in a seed starting mix to achieve the same results is still very much up for discussion. Other studies report that the quality and mix of ingredients and an assay to determine specifically what microbial agents are present and at work in the compost need to be considered when determining the effectiveness of compost in a seed starting mix to control damping off diseases. Since home gardeners have minimal control over exactly what is in their compost microbe-wise, just assuming any compost will have the same results is optimistic at best. And that doesn't address the other issues rampant with including compost to a seed starting mix, like creating an excessively moisture retentive medium. Overly wet soils are one of the primary factors in developing damping off problems in the first place.

So 100% incorrect information??? Not even close! It helps to actually READ the reports.

If making your own seed starting mix, it is far better to follow instructions for creating a lightweight, fast draining, sterilized mix than to experiment with what untreated compost may or may not contribute to the process.

– Use sterile well drained soil mediums. Avoid wet or compacted soil.
Raise seedlings in treated commercial growing compost. If home-produced
compost is being used, steam-sterilize the compost to destroy pathogens.
Soil mix has to be held at 140 deg. F for at least 30 minutes to ensure
sterilization.

-- If starting plants indoors, in cold frames, or in greenhouses, plant seeds in steam treated soil or pasteurized
potting mix. You can purchase treated potting soil or prepare your own. Soil mix must be held at 140° F
for at least 30 minutes. UCDavis IPM

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Comments (11)

gardengal48 (PNW Z8/9)
9 years ago
Not sure where you are getting your recipe from but seed starting mix is typically a very finely textured, sterilized medium with no added fertilizers. Seeds need no fertilizer to germinate and grow into seedling stage - everything they need is contained in that seed embryo. Seeds can't photosynthesize, so they have no use for fertilizers nor the ability to assimilate them.

I would simplify your recipe to equal parts peat, perlite and vermiculite. This mix will be light, sterile and moisture retentive while still offering decent drainage For 15 gallons, you would need 5 gallons of each. Adding compost eliminates the sterile component, which opens up the possibility of common seed starting diseases like damping off or fusarium, as well as impeding drainage.

Once the seeds have germinated and are a couple inches tall with their second set of true leaves, repot them into a regular potting soil to grow on until they are ready to plant out. You can fertilize with a dilute liquid fertilizer at that time and with every watering.
drew51 SE MI Z5b/6a
9 years ago
The mixture sounds fine to me. Once the first true leaves appear plants can uptake fertilizer, and many commercial mixes for seeds contain fertilizer.

Also numerous studies show compost suppresses damping off, not cause it. That is 100% incorrect information given.

http://cwmi.css.cornell.edu/organicfarmingfinalreport.pdf

Just google compost and damping off and you will find hundreds of reports that indicate the benefits of compost.

Here is a great study of compost and root rot

http://www.hindawi.com/journals/jmy/2013/324570/
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DWD2, thank you for posting your methodology. It always good to see how others grow their seeds and compare methods. I have grown my own starts (36+ tomato varieties) for the past 5 years. Before last year, I had not had too many plant health problems, except for the first year when my light system was not close enough to my plants. In that year I had problems with leggyness. I strongly suspect that my problem last year was the seed starter mix, but it could have been a few other things. I may have introduced disease into the first batch by incorporating compost into the mix. I think this is unlikely because in other batches and other treys I did not use compost in the mix but still had the same problems. Also, once the plants were in the ground they recovered and grew well the rest of the summer. If it were a disease I would have expected that the plants would still have had problems after planting, which they did not. Tomatoes are really amazing in what they can take early on and still produce well. For example, I had a mouse eat all the leaves of two plants shortley after they were in the ground. There were only stems left and I thought they were done, but I did not pull them out. Both plants sprouted new leaves again and became bushy healthy plants. I was astounded. I have had others suggest that with an approximately 50/50 mix of vermiculite and peat, I may have had water retention problems that suffocated the roots. Thats possible, but I was pretty careful about my watering. I can't totally rule that out. It may also have been too many nutrients from a dilute solution of fertilizer at watering as the problems occured shortly after that. I have read that new seedlings don't need many nutrients becuase they get what they need from the seeds/cotyledons. Some have even suggested that you will cause more problems by fertilizing than just not fertilizing. The reason why I fertilized is because we had a number of storms in May that pushed my planting date back 3-4 weeks longer than our average frost date. So I fertilized a little. I may also have had root binding problems. There is another possiblity which DWD2 suggested. I used a seed heating matt for the first time last year and most of the tomatoes had it under them for at least a day. So I may have over-heated the soil a little and damaged the roots. However on the last seed trey that got started late, I did not use the heat matt because I suspected it may have caused the problems. Yet I still had the same problems in the last trey. My strongest suspicion is still the starter mix. I have read the ingredient list on several seed starting mixes. In most cases, they usually contain peat (as the main medium plus it has high cation exchange capacity) + vermiculite (for micro nutrient exchange and water retention) + lime (to balance the PH of the peat). They sometimes include perilite, but sometimes not (example Jiffy), they also sometimes include a few other things (mycorrhizae for example or a source of nutrients). The main ingredient that I was missing that most starter mixes have is lime for ph balance. I could not find lime in any stores in Utah at the time. They do sell it here, but it is not a common soil amendment in Utah because most Utah soils are slightly alkaline (PH 7.8-8.2). So most folks would not want to add lime. This year I am interested to try mixing my own starter again but I wanted actual recipies to get an idea of the right proportions to use. Also I had no idea that mycorrhizae was available so I am defintley going to use that in my mix. Alternatively I could just buy a pre-made starter mix, but I wanted to save money and its a learning experience as well.
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zeuspaul
9 years ago
15 gallons divided by 6 equals 2.5 so each part is 2.5 gallons. Two parts is 5 gallons.

So if you choose to use that recipe, 5 gallons peat, 5 gallons compost, 2.5 gallons perlite and 2.5 gallons vermiculite.

15 gallons is two cubic feet. Don't worry about dry vs wet.
mblan13
9 years ago
15 gallons of seed starting mix? WOW! you're a lot more ambitious than me!

I use my "lazy method".

I put regular 5-1-1 (ish) and use a dibble to make a cone shaped depression (making sure the soil is sufficiently moistened to hold its shape) and fill the cone shaped depression with sterile bagged seed starting mix. The seed sprouts in the seed mix, then grows into the 5-1-1 when it gets bigger.

Bob's your uncle, Fanny is your aunt and there is no mucking about transplanting seedlings!
drew51 SE MI Z5b/6a
9 years ago
last modified: 9 years ago
I stand by what i say, try it both ways then tell me I'm wrong. I see a day when sterile mixes are a thing of the past, old school bigtime. If you go to the research sites you will find thousands of studies. not just hundreds. I would take your own advice and read the studies.
gardengal48 (PNW Z8/9)
9 years ago
I'm not going to argue with you- that is obviously pointless. What you predict is in your own imagination, nothing that is yet verifiable.

btw, plant science is my business - I am a professional horticulturist - and I do keep abreast of all the technology. And the research cites (not sites) number in the dozens, not hundreds, let alone thousands.
drew51 SE MI Z5b/6a
9 years ago
last modified: 9 years ago
Site refers to website. It must be tough to always be wrong!

http://dictionary.reference.com/browse/site?s=t

Humans are so funny, in nature are seeds germinated in a sterile environment?
No, so let's forgo millions of years of evolution and do it our way. Ha! I'm a
research scientist, or was I worked for MSU and Sparrow hospital. I'm retired
now. Horticulture is more a trade than a profession for many. I suppose if you had a masters or higher, then yes a profession.

Here are my seedlings started in a compost mix. Peppers and tomatoes, now in a homemade potting mix described below. Let see yours?

Fig cuttings in a compost mix with pine, peat, DE, and perlite.

Some more seedlings
gardengal48 (PNW Z8/9)
9 years ago
If research cites (quoted authorities, typically stated at the bottom of research papers) only number in the dozens, then it stands to reason all those "hundreds" of websites are just repeating the same thing from the same sources. Still trying locate all those hundreds, btw..........not coming up with anything approaching those numbers with even advanced searches.

And since you are so intent on definitions, take a gander at 'profession': a paid occupation, especially one that involves prolonged training and a formal qualification.

Let me see.......I have a degree, have spent more than 20 years practicing my "trade", taking additional classes and specialized training, have qualified for and received state certification and I am paid for it. Seems I qualify as a professional on all fronts!

And it would seem to me that a trained scientist would understand the implicit difference in plants growing untended in nature and those manually cultivated by humans. Totally separate conditions that cannot be compared equally. Apples and oranges.

It would also help your arguments carry a bit more weight if you weren't quite so demeaning and rude in your responses.
jane__ny
9 years ago
I've been starting seeds for over 40 years. Lots of flats for large seeding areas. I have started flats indoors and outdoors. I could not afford to buy or mix a sterile mix which frankly, is not possible. I don't understand what Gardengal is talking about. Unless starting seeds inside a bubble, nothing is sterile. The flats, the water, the air.

So, I tend to agree with Drew. Use any fine soil indoors. Outdoors use whatever you can get. Sow your seeds and give them good light.

Jane
drew51 SE MI Z5b/6a
9 years ago
Sorry to be rude, I was, as Jane says one can still get the fungi even in sterile mixes, it's all over. Compost gives at least gives some degree of protection, and studies have shown it works. All I should have said. Another way to keep it down is to cover surface of soil with sand or vermiculite. The fungal spores splash unto the plant. Bottom watering helps too. I have found those bottom watering wicking mats work well. Btw I too have been doing this for over 40 years. Nothing trumps experience.

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