How to Make the Best Potting Mix for Starting Seeds

, written by Benedict Vanheems gb flag

Making a potting mix

It’s that time of year again: seed sowing time! Sowing the first seeds of the growing season is incredibly exciting – just think of all that fresh, tasty homegrown produce to come!

To sow into containers you’ll of course need some seed starting mix, and a good mix can prove costly. Unless, that is, you make your own.


Seed Starting Potting Mix Recipe

The perfect seed starting mix mustn’t be too high in nutrients, which could harm delicate seedlings. The mix should also hold onto moisture without becoming soggy. Overly wet conditions can rot seeds and encourage fungal diseases such as damping off.

Our seed starting mix uses a soil-less recipe, so it’s beautifully light and fluffy and will promote good, strong growth and happy seedlings.

Begin with two parts compost as your base. All parts are measured by volume, so it doesn’t matter what you use to measure your ingredients, so long as you’re consistent. The compost slowly releases nutrients into the mix, which will help to feed seedlings as they grow. You can use your own garden compost, or buy some in. Break up clumps with your hands or, better still, screen or sieve the compost to get a fine, even texture.

A simple potting mix of compost, coir and perlite gives seeds an excellent start in life

Now add two parts coir (coconut fiber). Coir is extracted from coconut husks, making it a sustainable, plentiful alternative to peat or peat moss. Extracting peat damages fragile ecosystems and contributes to climate change, so we like to avoid using it. If your coir has come in a block, rehydrate it first by soaking it in a bucket with water until you can easily break it apart. If you prefer, you could substitute well-rotted leaf mold in place of the coir. Both coir and leaf mold contribute bulk to the seed mix, and are great for moisture retention.

Finally, add one part perlite, which will both lighten the mix and improve its air content. If you prefer not to use perlite then you could substitute sand, though it will give a heavier mixture.

Adding perlite to a potting mix helps to improve its structure

Use a spade or your hands to mix all of the ingredients together. Take your time and be thorough – you want a consistent mix, with all of the ingredients evenly distributed. Once you’re done, store the starter mix in either a lidded container or in old potting soil sacks (or any other strong plastic sack) with the top rolled down tightly and secured. Store your mix in a dry, cool place.

Using your Seed Starting Mix

Moisten the seed starting mix before you use it, so it’s damp but not sodden. The mix can be used in plug trays, plastic pots, seed flats, or any recycled containers suitable for seed sowing.

Gently press down your seed starting mix as you fill your container, and take particular care to properly fill at the corners. Top up with more mix if required. Don’t worry, this mix isn’t easily compacted so don’t be shy about firming it down so there’s enough mix for roots to explore.

Sowing into plug trays of potting mix is an easy way to start seeds

Sow your seeds according to the packet instructions, then water. Watering requires some care – you don’t want to blast the mix out of the container, so use a mister or a watering can fitted with a very fine rose. Alternatively, make a watering bottle by piercing holes into the cap of a plastic bottle using a pin. Fill with water, screw the cap back on and you’re good to go.

Once the seedlings have germinated it’s best to water from below. Sit your containers in shallow trays of water for a few minutes until you can see the surface of the mix is moist. Remove containers from the water once you’re done so excess water can drain away.

Many seedlings need potting on into larger containers at least once before it’s time to plant them out. Most will be happy potted on into the same seed starting mix but hungrier seedlings like cauliflowers or tomatoes will appreciate something a little richer. Adding some worm compost to the mix like this gives it just the nutritional boost you’re after.

Potting Mix for Containers

Try this simple potting mix for plants to be grown on in larger containers. Thoroughly combine two parts garden compost with one part coir or, better still, leaf mold. Now add some perlite for drainage – about two to three generous handfuls to every 10 gallons (45 liters) of the coir-compost mix. A similar amount of worm compost can also be added for hungry plants, or incorporate a slow-release organic fertilizer according to the manufacturer’s instructions.

Plants grown on in containers need a richer potting mix

Plants grown in the same container for a long time need a potting mix that holds its structure and is buffered against nutrient imbalances. Loam or good quality garden soil offers this. Simply combine one part loam – or screened or sieved garden soil – with one part garden compost then add some slow-release organic fertilizer. And that’s it – a versatile potting soil suitable for many containerized fruit trees, bushes and perennial vegetables.

Making your own seed and potting mixes like this can save you a lot of money. But perhaps most appealing of all is that you can tweak these recipes for what you’re growing. Of course, there are lots of other seed sowing and potting mixes out there, so if you’ve got one that works for you, why not share it in the comments section below?

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Show Comments


"Enjoy all of the info and ideas!"
Kathy Kutscherousky on Friday 9 March 2018
"Thanks Kathy, glad you've found it useful."
Ben Vanheems on Friday 9 March 2018
"DIY to me does not mean going to the shop, buying bags of stuff, bringing it home and mixing it. DIY means 'using whatever you have'! I don't have ANY of the ingredients you recommend, so I might as well buy it ready-mixed!"
My Name on Monday 29 October 2018
"That's a fair point. If you have your own leaf mould, however, you can really save a lot of money, adding only a few choice ingredients to make your own potting mix. Leaf mould is very much the 'DIY' element to this. In all cases, though, making your own potting mix, even when using bought-in ingredients, should save you money."
Ben Vanheems on Monday 29 October 2018
"In the east of Scotland, leaf-mould from deciduous trees needs two years to rot properly by itself; don't use evergreen tree leaves, e.g. Holly, as they rot much more slowly. Sycamore is good. Rake up in Oct., and Nov., make heaps, the bigger the better, near where you want to use it; aerate now and then by stirring and digging from the bottom; this definitely speeds things up. It's ready when you can put it through a quarter- inch sieve with ease. Lovely stuff, lovely smell! "
Megaloikos on Friday 4 January 2019
"Sounds like you've got leaf mould making down to a fine art. It is wonderful smelling stuff isn't it!"
Ben Vanheems on Friday 4 January 2019
"We started a worm bin a couple of months ago - can the worm castings be used instead of the compost?"
Kat on Friday 25 January 2019
"Worm castings (also known as vermicasts) are much higher in nutrients that compost, so aren't a perfect substitute for general compost. Worm castings won't 'burn' or damage plants though, so they are safe to use in quantity and are a great way to give a boost of nutrients to plants. However, it's quite a precious material - you don't get much of it generally - so use it wisely as a top-dressing around plants or lightly forked into the soil, in much the same way you would with any fertiliser. General compost is best used in bulk - to also improve soil structure, as well as nutrient content. "
Ben Vanheems on Monday 28 January 2019
"MAKE THE BEST SEED COMPOST. Thank you for the info on seed compost, I will be using that ingredients this year [2019] what I would like to know is what size sieve do you recommend, I have just bought a 3in1 sieve 3mm 6mm and 9mm"
les on Friday 1 February 2019
"A 3mm sieve is probably too small for sieving compost, so go for the 9mm or 6mm gauge sieve. The latter would be best for very find seed compost."
Ben Vanheems on Monday 4 February 2019
"If making your own compost from loam / garden soil, what advice would you give to get rid of the "resident" weed seeds that are already in the soil before planting your seedlings? Is it worth to allow the soil to cultivate the weed seeds for a few weeks prior?"
John Clarke on Saturday 16 February 2019
"If making your own compost from loam / garden soil, what advice would you give to get rid of the "resident" weed seeds that are already in the soil before planting your seedlings? Is it worth to allow the soil to cultivate the weed seeds for a few weeks prior?"
John Clarke on Saturday 16 February 2019
"You have a few options. You can spread it out and allow any weed seeds to germinate before removing and using. Or you can sterilise the soil in an oven or microwave, by raising the temperature of it to kill of any lurking weed seeds. Of course, sterilising in this way is only really practical for smaller batches of soil."
Ben Vanheems on Thursday 21 February 2019
"Thank you for your advice. Could you use vermiculite instead of perlite. Also, in regards to the measurements. If I add a 9L coir-peat. Then what would 2 part compost be - 18L? Thank you for your help "
Helen Nomlatyu on Saturday 9 March 2019
"Hi Helen. You could use vermiculite in place of perlite. And yes, two parts would be twice the amount - so if it's one part coir, then two parts compost would be twice the amount of coir. "
Ben Vanheems on Monday 11 March 2019
"Great article! Would this suggested seed starting mix be considered organic for veggie seedlings?"
Stephanie on Monday 26 August 2019
"Yes, if the ingredients used to make your mix all come from herbicide and pesticide-free sources and contain no artificial fertilisers, then you can consider the mixes to be organic. Certainly the seed starting mix would be organic, as you are only using compost and coir or leaf mould, plus the perlite."
Ben Vanheems on Friday 30 August 2019
"Very helpful, thank you"
Anthony Worthington on Saturday 30 November 2019
"What is the best soil to buy that is already prepared? Can you use glass containers to sow the seeds in?"
rt on Sunday 1 March 2020
"It's hard to recommend specific brands, as these will vary across regions. But if you are looking to sow seeds then any seed starting mix/propagation mix would be perfect. Or for more general use an all-purpose/multi-purpose potting mix, which you can sieve for seed sowing. You can use any container for sowing into, so long as it has drainage holes at the bottom."
Ben Vanheems on Monday 2 March 2020
"Thanks for the information and clear pictures! Have not started from seed for many years, so wanted a brush-up and you inspired me to switch from peat to coconut coir. Thank you for helping this gardener run a cleaner garden with fewer environmental impacts. What kind of containers are you using and what do you recommend?"
Christina on Friday 27 March 2020
"For sowing I recommend a few types of container. Simple 3-4in (7-10cm) wide containers are great for sowing seed like tomatoes, which are then pricked out/transplanted into their own pots once they are big enough to handle. For vegetables or flowers you will be growing a lot of, a seed tray works well, giving more surface to sow into. But I wouldn't be without plug trays, also known as module trays. You can sow one seed or a tiny pinch of seeds per plug/module, then grow the seedlings on until they are ready to plant out. This avoids having to prick out seedlings and is great for many crops, from salads to cabbage."
Ben Vanheems on Monday 30 March 2020
"Thanks for this information - it is just what I needed. I have everything in my garden except perlite, but I can get fine pumice locally so that will be everything at no cost! "
Chris on Sunday 17 May 2020
"That's great Chris - how satisfying to make your own potting mix for absolutely nothing!"
Ben Vanheems on Sunday 17 May 2020
"Found a bounty of worm castings by pulling weeds on concrete steps, now to put them to work, very informative article! Thanks"
Julie Mercer on Saturday 23 May 2020
"Glad it was of use Julie."
Ben Vanheems on Monday 25 May 2020
"If I were to use rice hulls instead of perlite, what is the ratio I would add?"
maggie on Tuesday 1 December 2020
"Hi Maggie. Rice hulls have much less of an ability to hold air and open up your potting mix than perlite. This is because the particles are much flatter. You may therefore have to add more rice hulls to have the same effect, but proceed with caution, perhaps testing a few different ratios to get the right mix. The Perlite Institute website has a handy document comparing the properties of perlite with alternatives, including rice hulls - just search the resource library on their site."
Ben Vanheems on Tuesday 1 December 2020
"Thank you for a well articulated post. Wonderful to find an alternative to the “peat” based mixes readily available at local box stores. I just spent a ridiculous $17 for a seed packet of “Valentine” tomatoes. Hoping for a miracle in germination to justify the cost. Will follow your recipe and hope for the best."
MaMa on Wednesday 20 January 2021
"Very best of luck with your tomatoes. That is a princely sum for a packet of seeds!"
Ben Vanheems on Wednesday 20 January 2021
"Thanks for the helpful article. I currently have my seeds (tomato, pepper, etc.) germinating in Seed Starting Soil made by Burpee. I want to put them in bigger containers after they start growing, until I can get them into the garden after the frost threshold. I would like to be able to use the materials I already have on hand, if possible. I have peat moss, leaf mold, compost and aged horsed manure. It's not completely soil free, because I mix the native soil into my compost. What do you recommend, without buying more materials? Thank you in advance. "
Jimmy on Sunday 28 March 2021
"I would add two parts compost to one part leaf mold. This should be fine for your tomatoes and peppers for a few weeks until you plant them outside."
Ben Vanheems on Sunday 28 March 2021
"Thanks so much, I’ve used this mix to start off all my veggies this year. Can I reuse the mix for more seeds once I’ve pricked out, potted on etc.?"
Ben on Thursday 8 April 2021
"Possibly. If the seedlings germinated really quickly and were moved on fast (for example salads and brassicas) then the potting mix won't have had much use out of it. I'd be inclined to reuse it, particularly if the seedlings were 'clean' and strong. You could always mix it in with a little more fresh mix."
Ben Vanheems on Tuesday 13 April 2021
"Thanks for this super helpful article. If sowing seeds outside straight into larger containers (eg 12 inch pots), is it best to use 2 parts compost to 1 part coir, or 2 parts compost to 2 parts coir as per the seedlings mix? If the latter, then do you need to add something further to the pot as the plant grows? Can most veg be grown straight into big pots once the frost has passed, or are there some vegetables that really ought to be started off in seed trays or modules first? Thanks."
Anne on Wednesday 14 April 2021
"Hi Anne. You could likely get away with sowing them straight into the mix designed for bigger pots. The reason seedling mixes are lower in nutrients is to avoid 'burning' the young roots. If you wanted to be on the safe side, you could fill the containers with the mix for containers, inclusive of the organic fertiliser etc, and then just finish it off with a top layer of the seedling mix, into which you sow. That way the seedlings will start off in their lower-nutrient mix but then reach down into the richer mix as they grow. I would make the seedling mix layer about 1-2 inches (3-5cm) thick."
Ben Vanheems on Monday 19 April 2021
"Layering over the top with seedling mix is a great idea! Many thanks for that suggestion. I'll definitely do that."
Anne on Monday 19 April 2021
"No problem. Here's to a very successful growing season for you! :-)"
Ben Vanheems on Monday 19 April 2021
"Thank you for this information. It was very clear and exactly what I need. I’m going to check on my leaf moulds now. "
Helen on Saturday 24 April 2021
"Thank you so much for this informative video. I have just bought some very rare and hard to get seeds and I am scared to ruin them. Once my plants get going I don't have many problems but getting these seeds started is worrying me. Thanks once again."
Mariss on Wednesday 28 April 2021
"You're very welcome Mariss. Good luck with your seeds!"
Ben Vanheems on Thursday 29 April 2021
"Hi firstly i do not think anyone has the right to be nasty regarding going out and buying materials to mix at home, I have a large garden and like any gardening person i like to know what 's in the mix also to go out and by certain materials to make these mixes for the likes of seed sowing in my case is a lot of seed compost and to know what to use and how to mix these materials will save me a lot, Your doing a great job and as i am 72yrs and been gardening for many many years im asking you to continue to do what you are doing (passing on good info)"
Daniel on Tuesday 4 May 2021
"That's very kind of you Daniel. I'm so pleased you find the articles useful and appreciate the thought that goes into them. Here's to many more years of gardening!"
Ben Vanheems on Wednesday 5 May 2021
"I found the comments/queries and replies really interesting."
paul white on Monday 24 May 2021
"Hi Ben, thanks for interesting article, most useful as I have had some bad experience recently with commercial compost which contains amino pyralids so I am trying to make my own compost. I have a Hotbin for making my own garden compost. When I empty it, it is not fully composted so I either put it in a dalek style compost bin to 'finish off' for a few weeks (it gets a massive amount of brandling worms in it) or put some in the 2 top layers of my wormery, the bottom layer also containing lots of worms which then process the compost. The resulting material can then be sieved to use in potting mix. My question is, is this compost now to strong to use in seedling compost, as it is now 'worm compost' or can it be classed as 'garden compost'. Thanks."
Alan Corbett on Tuesday 22 June 2021
"Hi Alan. The compost that goes into a worm composter will be richer. This stuff is usually added to composts made for more mature plants, as a natural plant feed. You could still use it in a mix for seedlings, but I'd be tempted to dilute it right down with plenty of standard compost. "
Ben Vanheems on Wednesday 23 June 2021
"Hi, thank you for your very interesting articles and loved reading the comments/answers. I am looking to make some wildflower/meadow flower “seed bombs” with my grandchildren and wondered what soil you could recommend. Ive also read that you can wrap seeds/soil in clay to help protect until ready to propagate. I’d love your advice, many thanks"
June on Sunday 4 July 2021
"Hi June. Yes, you'd need something that is relatively sticky - so it forms a ball. So I would include clay in your soil. The soil that your seeds are held in within the seed bomb is really more for carrying purposes. They'll provide some initial support, but the soil you throw them into will have the most impact."
Ben Vanheems on Monday 5 July 2021
"i have quite alot of wood lice in my compost bin would it be ok to soak it with jeyes fluid before i use the compost"
tony ayers on Thursday 9 September 2021
"Hi Tony. Definitely don't do that. Wood lice are detritivores, which means they help to break down dead organic material. In other words they are very useful to the decomposition process and will actually be helping to speed things along for you. They are an asset to any compost bin and will move on once there's no more material for them to feed on. So keep them where they are!"
Ben Vanheems on Monday 13 September 2021
"Hi there, where did you buy your soil tub/container that you're using in the video to put into the seed tray? Thanks!"
Lindsay on Thursday 10 February 2022
"Hi Lindsay. Please forgive the time it's taken to get back to you - I hadn't been aware of your comment till now. The soil tub/container probably came from a household wares store - probably sold as a storage container originally. I'm afraid I can't remember where I got it from exactly, but I imagine these sorts of tubs are widely available."
Ben Vanheems on Thursday 28 April 2022
"I’ve used a pre made seed starter mix for years and find at first it is very hard to saturate thoroughly as water often pools on top and then drains very slowly often not wetting the entire way through the plug. After reading your article (and watching the YouTube clip) I did a little experiment comparing your homemade mix recipe and the pre made version I normally use. The homemade mix was much easier to saturate, water flowed through and didn’t pool. The mix stayed moist for longer and required less top ups. The seeds I planted in the homemade mix germinated 1-2 days earlier. I found that the germination rate was about the same (I put that down to temp, seed quality and weather conditions not soil). The overall cost worked out cheaper per 10L bucket I used. Using all of the ingredients in the homemade mix cost me $19.18 AUD and made me at least 90L of seed starting mix. The pre made mix I normally use is $12.57AUD and is in 25L. I’m saving a lot and got quicker germination and it required less watering top ups, WIN WIN in my book. Thanks Ben! "
Samantha Gregor on Sunday 19 June 2022
"Thanks Samantha. This is a real endorsement of the homemade mix, and really reassuring to read you're getting such good results. As you say, a win-win all round! Thanks so much for reporting back on your findings. :-)"
Ben Vanheems on Sunday 19 June 2022
"Love this. I’ve never been able to see the value of sterile seed raising mixes with no added nutrients - they just have never worked for me. Can’t wait to try it (Spring right now in the southern hemisphere). Thank you!"
Rosemary on Sunday 9 October 2022
"Is peat moss ok to use for potting mix"
Robert W Ives on Saturday 4 March 2023
"You can use peat moss for potting mixes, but I try to avoid it due to environmental concerns. It's a valuable wildlife habitat, and digging it up releases carbon, contributing to climate change."
Ben Vanheems on Monday 6 March 2023

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