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How to make seed compost for starting seedlings

Last updated on April 6th, 2022

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This is the season for seedlings. Now is the time for germinating them in your home or greenhouse, which of course requires good seed compost. The problem is most compost types (including multipurpose compost) you can buy from garden centres and nurseries are not ideal seed starting mixes. You have probably had some plants that no matter what you did, just did not germinate. They seemed overly watered on top but dry to the bones down below. 

The cause? If the compost mixture isn’t right, it can lead to bad water absorption, something that proves fatal to your new seeds because they can rot before they start. If the nutrient content is wrong, it will hinder root growth and seedlings need very little nutrient value at first. 

Plus, it’s expensive. No matter where you look, high-quality compost is expensive. 

To that end, knowing how to make seed compost for starting seeds can prove very useful, especially if you are going to germinate from seed, season after season. 

The perfect recipe for germinating seeds

To make anything, you need the perfect recipe. The seed starting mix needs to be low in nutrients, hold onto moisture without becoming soggy, and it needs to be light and fluffy so the roots can penetrate and spread without much resistance. 

Getting the base mix right

Start with the base of your mixture should contain two parts of compost. When reading this compost mix, be advised that the parts are based on volume, so whatever amount you are making, you can keep to the same volume and ratio. We recommend just using a large jug to scoop the correct amounts in equal volumes.

Use 2 parts compost that has been sieved with a riddle

Compost will release nutrients slowly, something the growing seeds need. Break apart the compost with your hands, but we do recommend using a compost riddle to make it as fine as possible. 

Mix the compost with 2 parts coir

Mix in two parts coir, or coconut fibre. This is what often lines store-bought wireframes for hanging baskets and it is a great alternative to peat moss, and we are always trying to find good alternatives to peat to do our part to help the environment. While peat moss is the normal additive here, it is not a sustainable product to use while coir is, which is why we recommend it. 

If you order coir and it arrives in a block form, you need to rehydrate it in a bucket of water until it breaks apart. 

CANNA Coco Professional Pro Soil 50L
  • High quality, cleaned and pre-treated coco coir ideal for pot culture or other bulk uses
  • Very easy-to-use and gives great results
  • A pure, organic product with a homogeneous structure and has had a full buffering, eliminating the side effects of growing on coir
  • Free of harmful viruses and soil diseases, thanks to CANNA's unique production process
  • Complex water/air system that that provides the ideal conditions for growing plants

Finally, add one part of perlite to the mix

Lastly, add one part of perlite to improve air content and lighten the mixture. Sand is an alternative to perlite, but it will produce a heavier mix.

PLANT!T Perlite 100L Bag
  • PLANT!T Perlite can be used for soil conditioning – increasing aeration and drainage in heavy, hard to manage soils
  • Repairing/laying down lawns – PLANT!T Perlite gives additional aeration and drainage when raked into spiked holes
  • Planting trees and shrubs – loosens and aerates soil to encourage root development
  • A natural, pH neutral and sterile growing medium derived from volcanic rock
  • Aid nutrient uptake and improves plant health and growth. Available in 10L and 100L bags

Mixing the compost mix

When you have all your ingredients, you need to mix them thoroughly. Use your hands for better tactile engagement and thoroughness; the more consistently mixed the better. When you are done, store your mix in a lidded container or thick plastic sack in a cool, dry place. 


Germinating seedlings

When it comes time to use your homemade seed mix, moisten it so that it is not too sodden, but not too dry either. Use recycled containers, seed trays, or module trays and gently press down on the mixture as you fill your container of choice. Consider using a heated propagator to improve the germination rate and speed up the process.

Stewart P035B Essentials Electric Propagator, 52 cm - Black
  • 52 cm heated propagator
  • Non thermostatic - simple on-off control via mains
  • Clear cover with adjustable ventilation
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Be sure to sow the seeds according to your packet instructions and water afterwards. Rest assured this mixture can be used as you transplant young seedlings and is something you can make year after year.

Would you rather buy seed compost?

Bestseller No. 1
Levington John Innes Seed Compost 30L for Sowing Seeds, Striking Cuttings, Delicate Seedlings
  • Ideal for sowing seeds, striking cuttings and delicate seedlings
  • Specially developed, with a high phosphate formula and 14 vital minerals for optimum root growth
  • Traditional mix of loom, peat, sand and fertiliser
  • Perfect for all seedlings
  • Approved by the John Innes Institute
Bestseller No. 2
John Innes Seed Sowing Compost by Westland Garden Health 10l
  • Perfect for bringing seeds to life
  • For fast, healthy germination
  • Fine texture
  • Helps retain moisture around seed
  • Balanced nutrient supply for seedlings
Bestseller No. 3
GREEN HAVEN Premium 20L Seedling Compost for Seed & Cutting – Compost for Plants Ideal for Seed Germination & Growth | Specially Formulated with Added Nutrients & Trace Elements for Healthier Plants
  • 𝐄𝐗𝐂𝐄𝐋𝐋𝐄𝐍𝐓 𝐐𝐔𝐀𝐋𝐈𝐓𝐘 – Our GREEN HAVEN compost for seed and cutting has been produced from the best quality moss peats from ecological managed licensed peat bogs and NOT from SSSI (sites of special scientific interest).
  • 𝐇𝐄𝐀𝐋𝐓𝐇𝐘 𝐆𝐄𝐑𝐌𝐈𝐍𝐀𝐓𝐈𝐎𝐍 – For fast and healthy germination, the GREEN HAVEN soil is packed with specially selected and graded soil. This blend of loam, peat, and grit with added nutrients provides the optimum environment for quick and healthy seed germination.
  • 𝐑𝐄𝐓𝐀𝐈𝐍 𝐌𝐎𝐈𝐒𝐓𝐔𝐑𝐄 – The GREEN HAVEN compost can keep moisture around the seed for a longer period. This compost soil is created with essential plant nutrients and water-absorption wetting agents, all of which enhance the plant's general health.
  • 𝐒𝐓𝐑𝐎𝐍𝐆 𝐏𝐋𝐀𝐍𝐓𝐒 – The compost is manufactured from high-quality soil, which aids in the development of stronger indoor and outdoor plants. Mixed with essential nutrients to maintain plant nutrition and aids in water retention to help plants grow greener.
  • 𝐌𝐔𝐋𝐓𝐈𝐏𝐔𝐑𝐏𝐎𝐒𝐄 – This compost is perfect for growing plants, vegetables, fruit, flowers, herbs, shrubs, and trees both indoors and outdoors. It can also be used to pot on indoor and outdoor plants, tubs, hanging baskets, and window boxes, as well as germinating and propagating seeds.
Bestseller No. 5
Pelle & Sol 60L Multi-Purpose Compost Soil Bag – Organic Soil Seed Compost, Nutrient Rich Compost Mix for Potting, Growing Garden, Outdoor, Indoor Seed Plants (60L)
  • 𝐇𝐄𝐀𝐋𝐓𝐇𝐈𝐄𝐑 𝐏𝐋𝐀𝐍𝐓𝐒: The compost is made from high-quality soil which helps develop stronger plants and keeps them healthy longer. This top-quality compost encourages strong root growth, and it helps grow stronger healthier plants. It is perfect nutrient balanced for seedlings.
  • 𝐑𝐄𝐓𝐀𝐈𝐍 𝐌𝐎𝐈𝐒𝐓𝐔𝐑𝐄: With added vermiculite, the compost can retain moisture around the seed or plants for longer. This compost soil contains essential plant nutrients and wetting agents, blended for water absorption, aeration and drainage which internal improves the health of the whole plant.
  • 𝐇𝐄𝐀𝐋𝐓𝐇𝐘 𝐆𝐄𝐑𝐌𝐈𝐍𝐀𝐓𝐈𝐎𝐍: A specially formulated blend of organic materials producing a long-lasting nutrient boost when growing your plants and benefiting the environment by enabling the reduction of the use of peat. It is perfect for all stages of a plant’s life ensuring a healthy life. This compost soil mix is ideal for all gardening uses.
  • 𝐌𝐔𝐋𝐓𝐈-𝐏𝐔𝐑𝐏𝐎𝐒𝐄 𝐔𝐒𝐄: This compost is suitable for indoor and outdoor, growing of plants, vegetables, fruit, flowers, herbs, shrubs and trees. It can also be used for germinating and propagating seeds, and the potting on of indoor and outdoor plants, tubs, pots, hanging baskets and window boxes.
  • 𝐄𝐂𝐎-𝐅𝐑𝐈𝐄𝐍𝐃𝐋𝐘 𝐂𝐎𝐌𝐏𝐎𝐒𝐓 𝐁𝐀𝐆: Comes with 60-litre bags of multi-purpose compost supplied in a recyclable bag. This soil bag is made from eco-friendly organic material which is reusable and helps the environment.

Last update on 2022-03-17 / Affiliate links / Images from Amazon Product Advertising API

Welcome to my site, my name is John and I have been lucky enough to work in horticultural nurseries for over 15 years in the UK. As the founder and editor as well as researcher, I have a City & Guilds Horticultural Qualifications which I proudly display on our About us page. I now work full time on this website where I review the very best gardening products and tools and write reliable gardening guides. Behind this site is an actual real person who has worked and has experience with the types of products we review as well as years of knowledge on the topics we cover from actual experience. You can reach out to me at john@pyracantha.co.uk

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