General gardening topics

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, Brown
  • 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
  • Adjustable ventilation panels for humidity and air temperature control
  • Sealed unit with an economical 22 W heater - insulated to retain heat within the propagator

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
John Innes Seed Sowing Compost Soil Bag In 35 Litres - Seedling Compost Bag - Nutrient Balanced Seed Compost Mix for Potting, Growing Garden, Outdoor & Indoor Seed Plants
  • 𝐏𝐑𝐄𝐌𝐈𝐔𝐌 𝐐𝐔𝐀𝐋𝐈𝐓𝐘 𝐒𝐎𝐈𝐋 𝐁𝐋𝐄𝐍𝐃: Our compost soil for plants indoors is crafted from high-quality organic materials, ensuring a nutrient-rich mix that promotes strong root growth and sustains healthier plants throughout their life cycle.
  • 𝐎𝐏𝐓𝐈𝐌𝐀𝐋 𝐍𝐔𝐓𝐑𝐈𝐄𝐍𝐓 𝐁𝐀𝐋𝐀𝐍𝐂𝐄: Specially formulated to provide the perfect balance of nutrients for seedlings, our compost for outdoor plants encourages robust growth and development, setting the foundation for thriving plants.
  • 𝐇𝐄𝐀𝐋𝐓𝐇𝐘 𝐆𝐄𝐑𝐌𝐈𝐍𝐀𝐓𝐈𝐎𝐍: Contribute to a greener planet by choosing our indoor plant soil compost, which is formulated to reduce the bad effects on the enviroment. This eco-friendly choice not only benefits your plants but also supports sustainable gardening practices.
  • M𝐔𝐋𝐓𝐈-𝐏𝐔𝐑𝐏𝐎𝐒𝐄 𝐔𝐒𝐄: Whether you're tending to indoor or outdoor plants, vegetables, fruit, flowers, herbs, shrubs, or trees, our potting compost is ideal for all stages of a plant's life. It's perfect for germinating seeds, propagating, and potting on plants in tubs, pots, hanging baskets, and window boxes.
  • 𝐂𝐎𝐍𝐕𝐄𝐍𝐈𝐄𝐍𝐓 𝟑𝟓-𝐋𝐈𝐓𝐑𝐄 𝐁𝐀𝐆: Each purchase includes a generous 35-litre bag of our seed compost outdoor plants, providing you with ample supply for your gardening projects. The convenient packaging ensures easy handling and storage, making it a hassle-free choice for your gardening needs.
Bestseller No. 2
Westland Gro-Sure Seed & Cutting Compost Bale - 20L (
  • Westland Gro-Sure Seed & Cutting Compost Bale - 20L
  • Product type: SOIL
  • Brand: Gro-Sure
Bestseller No. 3
Westland John Innes Peat Free Seed Sowing Compost 10L
  • For fast, healthy seed germination
  • Feeds for the first 3 weeks
  • Added vermiculite to retain moisture
  • Peat Free
Bestseller No. 4
Seed Sowing, Cutting & Planting Compost 60L - Specially Formulated For Germinating Seedlings & Planting Cuttings - Professional Blend which has 6 months feeding as standard - By Jamieson Brothers
  • PREMIUM MIX: Jamieson Brothers Seed Planting Compost 60L bag - A true premium mix only available online and offering clean, disease free seed planting growing media
  • EXTRA FEEDING ADDED: Enriched with nutrients to last up to 6 months to let your seeds get off to the best possible start.
  • WETTING AGENT: Wetting agent added to Improve water retention for stronger root and plant growth
  • SUITABLE FOR : Not only giving the best start too your seeds but can also be used for vgetables, fruit, flowers, shrubs, herbs and trees for healthy abundant growth and stunning results all around the garden or home. Enhanced Formula Helps Retain Nutrients and can be used in Pots, Tubs, Baskets, Beds, Borders, Raised Beds and Planters both indoor and outdoor.
  • ESTABLISHED IN SCOTLAND 1895: Jamieson Brothers were established in 1895 where we began selling our potatoes on a horse and cart. Nowadays we offer a range of gardening products for your every need, whether you’re a manufacturer growing vegetables at scale, growing vegetables at the allotment or garden for personal use, landscaping outdoor spaces or are a budding gardening hobbyist.
Bestseller No. 5
Levington PEAT FREE Seed Compost, with added John Innes, 25 Litres
  • For sowing seeds, striking cuttings, delicate seedlings
  • Peat-free: special coir and wood fibre combination for a finer texture and healthy moisture balance to aid germination
  • Unique balance of nutrients for stronger, healthier plants
  • Specially formulated with high-phosphate content for optimal root growth
  • With added John Innes, sand and loam

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