Seed germination issues, making own potting soil

HI, I have a question. I have been mixing my own potting soil using 1/3 vegetable compost, 1/3 peat moss and 1/3 compost manure. This has always worked for me! however the last mixes i have made last year with those same 3 ingredients has produced a potting soil that seems to contain some kind of seed germination inhibitor. The roots also don’t grow and half of the seed covers don’t slough off. I now seeds don’t need a highly rich soil to germinate in, but it always worked.

So what are the possible things in the soil that is causing seeds to not properly germinate? what should I be looking for? Other than testing i am hoping its simpler.

Thanks Elly

Hi Elly,

This link has a really good explanation of potential issues:

I’d guess it’s either too many soluble salts (high electrical conductivity (EC)) or acids in immature compost.

If you don’t want to test, I’d suggest doing a trial using some fast-germinating seeds in a small amount of mixes that exclude the compost manure and/or the vegetable compost. At least that way you could narrow it down to which material (if either) is causing the germination issue, and it will give you more information about what to do next.


Like Rob said, compost is the most likely culprit (due to high salinity). A soil test of your mix will let you know quickly enough, but (again, as Rob said) try to cut it out and see if that helps as that process of elimination will be quick and won’t cost you anything.

However, you may also want to consider that your water source could also be the culprit. Have you ever tested your water?

Awesome help! I have done a lot of reading and i think the problem is because i am adding too much manure into the compost box over the winter and spring time.

Water is only tested for bacteria . So where do i send water for testing for more than just the basic testing ?

I bought a bag of potting soil and mixed it with peat moss. I will know in the next week when the leeks pop thru if store bought potting soil is better. Unfortunately, here in my small town i don’t have a great choice for potting soil that doesn’t have fertilizer already added to it. So i bought Home hardware brand. There is no info on the bag, so hoping its free from fertilizer additives and its low in soluble salts.

Most people I know that do their own gemrination mix have an EC tester to make sure they get the right balance and salinity ends up being too high, though I don’t specifically recommend this one, I’m just providing the link as an example:

I do my water testing at A&L labs to get a full panel on it, though we use the same water for irrigation as well as for drinking water in the house, so I have a special interest in making sure the water is up to both standards. The test itself is fairly cheap.

Where are you located Elly?

Here is my own water test if you’re interested in taking a look. I also test coliform counts (and thus for e.coli) every few months for free through our county health unit.

Env-WELL_SAMPLE-C15065-60000-1.pdf (105.0 KB)

Thank Denis,

I took a look at your results. I have never seen a test result for water like this. so what are the most important things i should be looking at? And in your example, where are the problems that need to be addressed. All i can interpret is that pH seems a little high at 8.
thanks Elly

You are correct that my pH was a little high so I often mixed some rain water in with my well water when irrigating seedlings in the nursery just to balance it out a bit. Seedlings tend to be a little more sensitive to pH than fully grown plants. So for that reason I wasn’t that concerned about it when irrigating out in the field since on any given year (except 2016 of course) we get plenty of rain.

We had three main areas of concern for our water:

  • We use it for drinking water in the house
  • We wash and process vegetables with it
  • We irrigate crops with it
  • We may have eventually used it for livestock drinking water

There’s some pretty good documents out there as to what to look for in each usage case, and I’ll link a few below. But mostly I was worried about sodium levels (for irrigation), coliforms/e.coli (for potability), and various metals (toxicity for high levels of cadmium, zinc, manganese, etc.).$department/deptdocs.nsf/all/wqe11091

I too have had occasional seed germination failures especially in onions with my homemade potting soil which is similar to yours- and think it is the acids in the barnyard compost, I understand they can build up in it in storage ( I put buckets of compost in my root cellar in the fall so its ready in March and I don’t have to try and get into my frozen compost pile.)
So far no issues with anything else ( herbs, flowers and a wide variety of other vegetables). I am going to modify my mix from now on for onions and leeks.

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I had another thought about germination issues and that is that there are many factors affecting germination, not the least of which is seed viability and vigor- fresh seed germinates much more vigorously than older seed- and I noticed this year that even though my leek seed which i planted was only 1 year old it didn’t germinate near as well as some fresh onion seeds. If you buy seed from seed houses that germination tests their seeds to make sure that they meet Canada no 1 guidelines they should be good for that year. But it doesn’t mean the seed is fresh and it may not hold viability well for another year as they can sell older seed as long as at the time they test it ( fall) it meets the standard. The standard itself is different for different seeds- I can remember being surprised that for some seeds its around 70-80%. Unfortunately the germination standard rate table is difficult to find.on the internet but if you ask you seed supplier they can tell you what the standard is and what that lot of seed tested ( and the date). Seed storage from year to year can also greatly affect viability. The two factors are consistency in humidity and temperature, eg no fluctuations.