What kind of soil are you guys using to start your seeds out? I've been using a generic moisture control potting soil with fertilizer. I've been getting a lot of gnats with that but they don't seem to affect my seedlings. I also get a little surface green which I break up from time to time.(maybe overwatering?)

So what kind of mixes are you guys making and do you sterilize it? If so how do you sterilize the best way? Thanks

I use a mix of about 70% potting soil and 30% sand. Then, when that is mixed and pasteurized, I add about 5% 'ground up' raw sphagnum moss, which I assume to be sterile. I look for a good grade of potting soil, and, good to me means one that has what appears to be 60% coarse, loamy soil and 40% peat moss with very little forestry products in it. Maybe a little vermiculite and a very small amount of fertilizer is usually added in these good grade potting soils, but that's neither here nor there, as far as I'm concerned. The objective is to prepare a soil media mix that has very good drainage AND percolation since with newly sprouted seedlings, feeding is initially done from the bottom.

As far as pasteurizing the soil goes, there a two ways I do it. One method is using disposable aluminum pans and a conventional oven where I can get an ambient soil temperature of about 150'F for 2 hours. The other is using 1 gallon size freezer bags and a microwave where I get a higher temperature quickly and steam, which I depend on. For me, I prefer the microwave method. A gallon size freezer bag will hold enough for a gallon pot or 3 large size baggies. And once pasteurized in the bag, these bags can be stored until ready to use. When using a 1000 watt microwave and the bag sealed I use 4 charges over a 10 minute period: 2 minutes at full power--then 2 minutes soak, turn bag over--1 minute full power--1 minute soak, etc. over about a 10 minute period. You'll have to keep your eye on it until you 'get the hang of it. Keep the bags sealed tightly throughout. The air inside will expand and the bag will blow up like a balloon under power--that's normal. When finished, then open the bag, press air out lightly and reseal.

Gnats are usually harmless (usually get those when you bring plants in from the outside or if soil is not sterile). A little bit of green at the soil surface or on the inside of baggies after a few weeks is not uncommon either. I haven't found that to be a problem because usually by the time you see it, your seedlings are all up and well on their way anyway.

Remember, too, there are other media mixes, some soilless, that can be used to sprout seedlings. And, this is only my method. Other members may have different ways--it all comes down to what works best for you and your setup.

I forgot to mention anything about sand; I'm a little picky about what sand I use. I don't use builders sand. I've found it to run from too coarse to too fine. And sand, actually, does not drain well if it is too fine. I use 'playsand' such as pictured. That seems to have a consistent, coarse grain size that drains well. Dry aquarium pet sand might be ok also, but too expensive.
bag of Kolorscape

I'm one of those that doesn't pasteurise my mixes. I kind of like the lottery of what else comes up in my seedling boxes. Does pasteurising reduce damping off, Lorn?

Finding a good potting media is hard, and I always have my eyes open for promising looking sands/gravels. For some reason there doesn't seem to be anything commercially available in Australia that isn't basically composted pine bark or wood chippings. Sure there's stuff added, but the bulk of the mix is still composed of fine (and not so fine!) chippings.

So... resigning myself to what I can buy, I modify it with extra sharp sand (gravel) and/or peat and compost. A few years back I made my own seedling mix with coir peat and gravel. It worked fine. Had to be aware that nutrients needed supplying regularly (I like seaweed and fish emulsion), but as time went on the coir would wash out, leaving 2-3 year old plants basically growing in sharp sand - no rot! - but very hard to keep cool and watered.

(My seedlings usually start life in styrofoam boxes and remain there for 2-3 years as I have no where to plant them out. Those seedlings I then keep get potted into commercial potting mix in large plastic pots.)

The greatest resource I ever had access to for making seed mixes was tree fern and humus from the bush on the farm I grew up on... but such fantastic materials aren't always easy to acquire. Saying that, I've noticed recently that a company in Tasmania is making shredded tree fern available, so I'll buy that for my special babies and mix it with gravels and potting mix. If you can find leaf mulch it makes a great base layer in seedling boxes. Something my Aunt taught me was to crumble some charcoal over this bottom layer too - it is a great growth stimulant. I presume because it captures and holds nutrients from being washed away.

As Lorn says, there isn't just one way of doing things. The objective is to prepare a soil media mix that has very good drainage AND percolation... I'm sure we all agree this is the paramount issue. Although, that is kind of a bombshell: differentiating between drainage and percolation. Not sure what you're getting at here, Lorn, but I am guessing your definitions might be different than mine. Also guessing that most people see the two terms as the same, and some explanations would be helpful? Indeed, fine sand does hold too much water for our needs here, but given a sufficiently deep column, it drains very well.

No pasteurizing mixes for me, either. Not that it's a bad thing: I'm just lazy and don't feel I need to bother. While being more fastidious very well could produce better results, I'm happy with the organic a approach of allowing nature to balance things out. There will always be the competition between all the soil flora, good and bad. The whole point of pasteurization is to kill the bad organisms and leave the good ones intact. With this thought in mind, I theorize that baking soil to pasteurize it is better than the impreciseness of the microwave. Obviously, there will be initial hot and cold spots in the soil, and at least some the the good fungi will be killed, too. Not to mention that there is guessing involved with the final temperature of the microwaved soil. There would be a much greater chance of not reaching the goal of pasteurization, with only partial elimination of "negative" organisms, or sterilization and killing everything.

I forget now..... what is so bad about composted forest products? I've actually begun to use it more and more as a large component in my mixes in pots that need to stay airy for 3-4 years without repotting. The mixture of small and large pieces is exactly what I need, especially in my fritillaria seed pots. Large size (half inch plus) pieces aid immensely in the draining excess moisture, even when it is surrounded by tiny particles. This is also why it is good to have varying size mineral aggregates (sans fine sand).

So, as I do tend to deal more with species lilies with more widely varying needs compared to hybrids, my media compositions also vary accordingly, sometimes more raw grit and sand, sometimes more organic material, but always trying to maintain an abundance of air space within the mixes. The only thing I might do differently from the aforementioned 70% good potting mix to 30% sand, is to have that 30% include large pieces of mineral aggregate, too, like #2 and #4 size grits (in some situations).

When I speak of drainage and percolation here, I'm using them in somewhat the same sense: A soil mix that drains down 'fast' should also percolate 'up' fast (hopefully in all directions with good wetting ability). I feed my young sprouts and seedlings from the bottom so percolation is important to me, especially during the first month or two. Later on and after the seedlings are moved outside and I begin drench liquid feeding from the top, drainage plays a major roll.

I think composted forestry products are a great addition to media mixes if you're going to grow your seedlings all the way to (n + 4) or ( n+ 5), etc. That's more or less, pot culture. I grow my seedlings only through (n + 1), then set them out in the garden, so, I never really would get to take full advantage of the slow release of nutrients long term as you do, Rick. They do make the soil mix light and airy.

One note about the soil temperature with the microwave. The soil temperatures do actually reach 160'F on the ones I checked. Whether it's foolproof or not, I don't know for sure, but it's a step I take to maximize survival (hopefully). That's my objective all the way through ( n + 1), then mother nature and I will start the selection and culling process.

I admire those who like to parallel mother nature as much as possible with seeding. It's just something I don't do.

Thanks, Lorn.

Remember we have a lot of new forumists here. I'm sure they have no idea what you mean when you say n + 1, n + 2, etc.

Sure. Well, in simple easy terms, the letter (n) designates the year the seed is planted and a seedling begins. That first year growing cycle becomes year (n). The second growing season, or the year following, becomes (n + 1). So, as an example, a seedling sprouted in spring of 2013, would be identified as (n + 1) in 2014. And (n + 2) in 2015, (n +3) in 2016 and so on. Another example: the seedlings I sprout this coming spring, 2014, will go through 2 full growing seasons (this coming summer and the next) and transplanted in the garden in the fall of 2015. Those will be (n + 1) when I transplant them.

Awesome stuff so far guys! So regarding this 'n' system, I assume this labeling is for the purpose of taking notes such as seedling "x" bloomed in n+1 year and in year n+2 the blooms show more promise. That kind of stuff?