Soil Mix for Seedlings

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Joined: Wed Jun 21, 2017 1:01 pm
Location: Seattle, USDA-8b, Sunset-5

Soil Mix for Seedlings

Post: # 70851Post sarahconeill
Thu Jan 09, 2020 1:57 pm

Hi Everyone,
I'm getting a late start to my seed planting this year (my 3rd year!), but I'm wondering if I should change up my seed soil mix this time. My process is as follows:
Collect seeds and clean, plant in 3 inch pots in groups of 5. (I skip the refrigerator step because 1. kids would attack them and 2. outdoor temperatures are refrigerators in my locale.)
Lay on flats and place in unheated greenhouse against my house and wait for sprouts. Water when I remember (I have to improve this part).
Take out of greenhouse about march-april (dependent on temperature and sprouting).
Seedlings of worthiness are transplanted to 1 gallon pots sometime after July and at that point they get only potting soil.

My soil mix is currently 1/3 potting soil, 1/3 vermiculite, 1/3 sphagnum peat moss. With a little bit of cactus rock on top for visibility and reflectance. It has to work from germination through seedling stage but it seems like late spring and early summer a lot of them lack vigor and are prone to disease. Not much in the way of yellowing though. Any input is helpful!

Posts: 1878
Joined: Wed Dec 31, 1969 7:00 pm

Re: Soil Mix for Seedlings

Post: # 70859Post Don
Fri Jan 10, 2020 2:08 pm

I prefer perlite over vermiculite as there is less chance for mold to develop but I am not in an arid location.
What doesn't kill them makes them stronger.

matt lustig
Posts: 43
Joined: Sat Jan 28, 2017 10:05 pm

Re: Soil Mix for Seedlings

Post: # 70861Post matt lustig
Fri Jan 10, 2020 9:11 pm

If you go to the top of the forum webpage, you can search old threads on this topic with keywords "soil mix" or similar. There seem to be some good ideas posted.

Otherwise, I have just 2 comments:
1. For hardwood plants generally (including but not limited to roses) I prefer to make my own mix with a combination of aged "pine bark fines" (basically shredded pine bark, a main ingredient in many potting mixes), washed sand ("concrete sand" or "pipe bedding sand", but NOT fine sand), peat, and vermiculite. At least in this region, these ingredients are all reasonably inexpensive and can be bought in bulk (peat in bales, vermiculite in large bags, "pine bark fines" by the cubic yard, and sand by the ton). With a truck or trailer, sand from a quarry can be extremely inexpensive--last I was a local quarry, pipe bedding sand was costing me about $6/ton. The ingredients can also be tailored-mixed, based upon my opinion of the specific species' needs.
2. I have no experience with cactus rock, but I do like the idea of putting a top layer above the main potting medium. I prefer perlite or course sand on top. My impression (not to be confused with scientific measurements!) is that they both, by tending to be freely-draining and non-absorbent, tend to reduce seedling disease problems. I also feel that course sand (which I actually prefer over perlite for this purpose) also helps to keep seeds from shifting around in a pot...remember that a number of potting soil ingredients could float and are thus susceptible to shifting around in the pot during a heavy rain. Of course one doesn't want the layer of sand to be to thick, but I believe a thin layer is beneficial.

Again, these comments are for hardwood plants generally.


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