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Seed Starting 101: Soil Mix

May 13th, 2010

After choosing your containers, you’ll have to decide what kind of soil mix you want to use for you seed starting efforts. There are all kinds of options: store bought soil less mix, home mixed medium, soil blocker mix, coconut coir, and peat pellets. There are all kinds of ideas floating around about what you should use for starting seeds. Some people say you shouldn’t use compost in your seed starting mix, others say you should because it’s good for the plants. Some people are against peat for environmental reasons and claim coconut coir is the way to go. Some people prefer the convenience of peat pellets or store bought soil less seed starting mix, some people mix up their own.

Here at Chiot’s Run I like to mix my own and I have since the beginning. With the amount of seedlings I start I’d spend a fortune on starting medium if I bought it. After trying all kinds of recipes I settled on one that consists of 40% peat moss and 40% medium vermiculite and 20% worm castins (I’ve tried using coconut coir and haven’t been as happy with the results as I am with peat moss). I like to add some Dr. Earth Organic Starter Fertilizer as well (I use the directions on the package and mix it in at half strength). Seedlings don’t really need fertilizer until they get their first or second set of true leaves, and you can’t fertilize with full-strength fertilizer because you run the risk of burning the seedlings. Always use half strength when adding fertilizer to seed starting mix or when watering with fish emulsion.

I’ve also experimented with watering my seedlings with weak a fish emulsion every week or two instead of using Dr Earth Starter fertilizer. I prefer adding the starter fertilizer directly to my seed starting mix, it seems to give me better results and it saves me from remembering to add fish emulsion. Some people use this mix and add 30% peat, 30% vermiculite and 30% compost instead of a fertilizer (you can us perlite instead of vermiculite if you’d like, I don’t like perlite so I always use vermiculite). I don’t have a ton of compost so I save it and add it to the holes at planting time, I also use it in my homemade potting soil mix. Some people recommend only using sterilized compost or peat to start seeds, personally I would never sterilize my compost, pear or anything I’m using to grow plants, part of the value of is the microbes. But I also drink raw milk, so I’m a big believer in the beneficial microbe world.

The main reason I mix my own seed starting mix is to save money. I buy the peat moss and vermiculite at my local farm supply store (the drive-thru feed type store). It costs me about $25 for 8 cubic feet of final seed starting mix. I like to mix it up in small batches in plastic storage containers. I make sure to mix up a batch in the fall and store it in the basement for late winter seed starting mix.

Whether you mix your own, buy it in a bag, or use peat pellets, your seed starting medium will need to be wet before you can plant your seeds. It’s often difficult to get peat to absorb moisture if it’s really dry. The vermiculite or perlite helps it absorb moisture and using hot water is also very beneficial. I warm water in my small teakettle and pour it on the dry mix. I keep adding water till the tray feels heavy and the soil is nicely moistened. If I add too much water and there is some collecting in the bottom tray I usually wait an hour then pour out any excess water. I also like to wait a day before adding the seeds to allow some of the moisture to evaporate, too much moisture is the most common seed starting problem and it can lead to disease problems. Then I plant the seeds according to their needs.

What’s your favorite seed starting medium? Do you have better luck with one kind of soil? Do you mix your own?

The rest of the Seed Starting 101 Series
Why Start from Seed
Getting Started
Soil Mix
The Needs of Seeds
My Workflow
Diseases and Problems
Hardening Off
Learn More Each Season

Visit my Amazon store to see what seed starting supplies I like.

21 Comments to “Seed Starting 101: Soil Mix”
  1. Mija on May 13, 2010 at 8:31 am

    Good Morning! I just wanted to say you are doing a fabulous job with this series of posts. Your generosity of spirit is so wonderfully refreshing. I feel truly blessed to have found your blog. Thanks for all you do – it’s a bright spot in my day! :-)

    Reply to Mija's comment

  2. Wider Sky on May 13, 2010 at 8:31 am

    Thanks for all this great advice.
    The weather here in the UK isn’t as warm as usual for this time of year (we’ve had frosts at night all week) so I’m having to start far more plants off in pots and trays than usual so all this has come at just the right time.

    Reply to Wider Sky's comment

  3. MAYBELLINE on May 13, 2010 at 10:59 am

    Wow – I like your recipe.
    .-= MAYBELLINE´s last blog ..Tomatoes Are In! =-.

    Reply to MAYBELLINE's comment

  4. Louise on May 13, 2010 at 11:24 am

    Susy, THANK YOU for posting this series. Seed starting is by far the most challenging aspect of my garden journey. I have, as of yet, not experienced the success with seed starting that I like to achieve; and your series is a great help. Thank you for sharing!

    I after some experiments of my own; I find that, like you, I work best with the plastic seed starting trays. I currently mix vermiculite, peat, and store-bought organic compost. I never sift the compost and therefore experience a problem with larger pieces of wood particles that are found in the compost. I believe this might be my problem. The seedlings might have to fight to much to make their way through these particles as they reach for the light.

    Another issue might be that most of the time I can’t wait to be out there gardening (in winter months) that I start my seeds to early; they become leggy and die off before I can give them the environment they need to further thrive.

    I do not sterilize my medium, but have read that a regular misting of Chamomile Tea can do wonderful things for young seedlings in regards to fighting off fungus.

    Thanks for sharing the info that you pre-moisten your seed starting medium with hot water. I have in the past moistened my soil with cold water when the seeds were already planted. So for my next seed planting session I will take your great advice.

    For the seeds that do not mind being transplanted I start them in moist white paper towel {without the inked images printed on it (ink is a serious chemical)} that I wrap in a plastic bag. To be transplanted in soil as soon as they sprout. I have success with sprouting the seeds this way, but the seedlings do not always make it. Do you have any advice on this?

    Again thank you for sharing all this info; visiting your blog is a highlight in my day!

    Reply to Louise's comment

    • Rita on March 13, 2011 at 4:14 pm


      Just read your post and I’m not sure what you’re using for lighting. If you’re using any kind of grow light, be sure it is no more than 4 inches from the starting seedlings. This helps keep them from getting leggy. Also, transplant after they get their first true leaves to slightly larger pots. You may have to transplant a couple of times before moving to the garden if you’re in a cold weather state like I am.

      Also if using artificial light, be sure to give the plants some “rest” time and turn the light off to give them approx. 4 hours of darkness each day. A plant does need to rest.

      Hope this helps.

      Reply to Rita's comment

  5. Lynn on May 13, 2010 at 12:40 pm

    Dear Susy,

    Wonderful and helpful series. Thank you for all your expertise and wisdom. I have a question. After your seedlings come up and fill out the cells do you transplant them into larger pots or put them directly in the ground and cover with row covers?

    Reply to Lynn's comment

    • Susy on May 13, 2010 at 12:54 pm

      It depends on the type of plant it is. Usually tomatoes I’ll transplant in another pot and peppers as well. Cabbages sometimes get planted directly in the garden. If plants can take the cold weather I often plant them outside ASAP. The sooner you can plant them in the soil the better they do.

      Anything that is tender gets kept on the porch and carried in the garage if the temp dips below 50. Usually I’ll plant tomatoes in the garden in late May, although we can still have frost until the first of June here at Chiot’s Run.

      Reply to Susy's comment

  6. mamaraby on May 13, 2010 at 4:03 pm

    I don’t know that I’ve necessarily settled on a favorite medium just yet. I’ve tried straight coconut coir. I liked that it came is compressed blocks that you just needed to add hot water to. I figured it was environmentally more sustainable with the added fact that it saved on carbon given you weren’t paying to ship all that moisture around. It fit in the shopping bag the regional home improvement store used for the 20% off anything you can fit in the bag sale which was an added bonus. I didn’t think, however, that the seedlings cared all that much for it.

    This year my husband was in charge. He started out with some Pro-Mix Ultimate Organic Mix we had on hand until we ran. He finished out with the Jiffy Organic Seedling Starting Mix which we most decidedly did NOT like. It was one of those peat moss is too dry and won’t absorb water kinds of messes.

    I always have grand plans to make my own mix and I’m sure it’d be cheaper, but in the end I’ll probably just go with the Pro-Mix again. It’s OMRI listed and the added with Mycorise® and a Sea-based compost seem to really help. I get it for around $6/cu ft which is more expensive than your mix, but still not all that bad. This year I plan on watching to see if it goes on sale and stock up at cheaper prices.
    .-= mamaraby´s last blog ..Carry a Big Stick =-.

    Reply to mamaraby's comment

    • Susy on May 13, 2010 at 4:10 pm

      I agree, my seedlings didn’t like to coconut coir. I also know that a lot of coconut plantations are sprayed with chemicals, so I don’t want that around my seedlings either.

      Using hot water definitely cured the “too dry” peat moss issue. I’ve heard of the Mycorise® before. I think the Dr Earth is similar since they both use all kinds of microbes in their mixes. I really believe these have been the reason for my success with seed starting. It’s like eating yogurt, super good for you and boosts your immune system.

      Reply to Susy's comment

  7. Colleen on May 13, 2010 at 9:26 pm

    I have been eagerly awaiting this series and am enjoying it! I too use peat and vermiculite, but have had a lot of trouble tracking it down. I ended up special ordering it from my local nursery, and paid about $70 for 4 cubic feet of vermiculite with 4.4 cubic feet of peat moss – so I choked a bit at your $25! Oh well. I have access to a city compost heap, with as much free compost as I want, so that helps to stretch the other ingredients.

    Reply to Colleen's comment

    • Susy on May 13, 2010 at 10:12 pm

      That is expensive. I have a really nice greenhouse located about an hour away and they sell 4 cu ft of vermiculite for around $18, from my local farm store it’s around $10. You should check to see if you have any local farm stores, even if you have to drive a ways you could stock up for a few years. I buy 2-4 bags of it each year.

      Reply to Susy's comment

  8. Dan on May 13, 2010 at 9:47 pm

    I have always bought potting soil and like you said it has cost a fortune. This year I am growing to try mixing my own.
    .-= Dan´s last blog ..Spring Update =-.

    Reply to Dan's comment

    • Susy on May 13, 2010 at 10:13 pm

      It sure does, I mix my own regular potting mix for growing plants as well. I’m very happy with the results of my homemade mix. Here’s my recipes for that: /2009/05/19/homemade-potting-soil/

      Reply to Susy's comment

  9. Renee on May 14, 2010 at 5:28 pm

    I had problems with growing tomatoes in the Jiffy peat pot soil – they ended up getting “damping off disease” (I believe that’s what its called) where their stems got all spindly and couldn’t support the plant. I planted them outside, burying the stem up to the leaves, and they eventually made a comeback.

    I think next year I’ll make my own potting mix as you suggested. Thanks for the tips!

    Is there anything wrong with using soil from the garden and just adding a bit of fertilizer and vermiculite to it for potting soil? Mine is slightly clay-ey.

    Reply to Renee's comment

    • Susy on May 14, 2010 at 8:45 pm

      Most people recommend not using soil because it doesn’t drain as well in a container, especially clay soil. I’ve also read it’s an issue with air for the plant in the soil. Plants need a little air around the roots. You could try adding some vermiculite to it to help lighten it. I’d recommend doing a side by side test. Plant a few seeds in some soil mixed with vermiculite and plant some in some seed starting mix, see what happens. If you do both you’ll be able to compare the two as they germinate & grow.

      Reply to Susy's comment

      • Renee on May 22, 2010 at 4:18 pm

        OK thanks, good advice!

        to Renee's comment

  10. Bruce on May 19, 2010 at 5:28 am

    That is expensive. I have a really nice greenhouse located about an hour away and they sell 4 cu ft of vermiculite for around $18, from my local farm store it’s around $10. You should check to see if you have any local farm stores, even if you have to drive a ways you could stock up for a few years. I buy 2-4 bags of it each year.

    Reply to Bruce's comment

  11. Deb Berning on January 17, 2013 at 12:45 pm

    The final product is expensive. Are these bags about3 ft. tall and 18″ wide and 3″ thick? I go through about 8 bags of 8 cf size. Could never do that. But then I grew about 350 plants last year mostly for myself, a few I sold. I start in larger pots to avoid replanting. That takes forever. Starting with 4″ diameter pots I only have to transplant tomatoes and sometimes peppers. Saves all the time and starting mix. Otherwise I’d go through probably 18 bags.

    Reply to Deb Berning's comment

  12. Betty819 on March 15, 2014 at 10:36 pm

    I don’t understand the part about 30% of this and 30% of that..I need that explained in exact 3 cups of this, 3 cups of that, add so many cups of something else..etc. Would you break down your instructions for me like that, so I can understand it?

    Reply to Betty819's comment

    • Susy on March 18, 2014 at 9:09 am

      Think about it as a whole, the reason I use the percentage is because it can be scaled depending on how much soil you need. Think about it in 10 cup intervals. So 30% of 10 cups is 3 cups. Or you can simply use whatever bucket you have. One bucket of peat moss, one bucket of compost, and one bucket of vermiculite then a bit of worm castings and fertilizer added in.

      Reply to Susy's comment

  13. marshall reagan on March 7, 2015 at 7:02 am

    I use a small cement mixer to mix my potting mix in because it does a real good job mixing it together . I had it setting outside my shop & decided to put it to use . I mix donkey manure in my soil with it after my chickens have pulverized it because the potting soil that you get doesn,t have much neutrient in it.

    Reply to marshall reagan's comment


This is a daily journal of my efforts to cultivate a more simple life, through local eating, gardening and so many other things. We used to live in a small suburban neighborhood Ohio but moved to 153 acres in Liberty, Maine in 2012.

Read previous post:
Seed Starting 101: Containers

Containers are a very important part of the seed starting system. There are all different kinds of containers, you can...