If you’ve ever stood in a garden centre, squinting at a 20kg bag of grass seed and wondering, “Will this be enough?” you’re not alone. Let’s explore how far that bag will stretch, and what factors might influence your results.
The Average Expected Coverage of Seed
A 20kg bag of grass seed typically covers 400 to 800 square metres, depending on the type of grass and its intended use. Here’s a rough breakdown:
Seeding a new lawn. Around 35 to 50 grams per square metre is recommended.
Overseeding an existing lawn. Requires less seed, around 20 to 30 grams per square metre.
This means a 20kg bag will cover approximately 400 square metres when seeding a new lawn, and up to 800 square metres when overseeding.
Varieties of Seed and Their Coverage
Different grass varieties vary in how densely they need to be sown.
- Perennial Ryegrass: A robust, fast-growing grass that needs around 40 grams per square metre for a new lawn. Perfect for family gardens or sports fields.
- Slender Fescue: Ideal for shaded or fine ornamental lawns, this variety can be sown more thinly, covering a slightly larger area.
- Creeping Red Fescue: Spreads via underground runners, so it needs less seed to achieve full coverage over time.
Always check the sowing recommendations for your specific seed mix—your 20kg bag might go further (or shorter) than expected!
Seeding a New Lawn vs Overseeding an Existing Lawn
The amount of seed you need depends heavily on whether you’re starting from scratch or giving an existing lawn a makeover.
New Lawn: The bare soil demands higher seed density to establish a full, even lawn. For example, 20kg of Perennial Ryegrass covers 500 square metres when creating a brand-new lawn.
Overseeding: A lighter application fills in patches and thickens existing grass. For the same seed, you might cover up to 800 square metres when overseeding.
How Soil Types Affect Growth and Seed Uptake
Soil type plays a big role in how well seeds germinate:
- Sandy Soil: Drains quickly but can dry out fast, so seeds may need extra water
- Clay Soil: Retains water but can become compacted. Loosening the soil before planting improves results
- Loamy Soil: The Goldilocks of soils, offering a balance of drainage and moisture retention for optimal seed growth
Adjust your watering and soil preparation to match your soil type for the best results.
Environmental Conditions and Their Impact
Beyond soil type, these factors also influence your success.
- Soil Health: Enriching soil with fertiliser or compost boosts germination rates
- Seeds on slopes can wash away. Use a seed blanket or mulch to help keep them in place
- Poorly drained areas may cause seeds to rot. Improve drainage before planting
- Mild temperatures (10-18°C) and consistent moisture are ideal. Avoid planting during heavy rains or heatwaves
Pests and How to Protect Your Seeds
Birds and other critters see your freshly sown lawn as an all-you-can-eat buffet. Here’s how to protect your investment:
- Bird Deterrents: Try netting, reflective tape, or decoys to keep feathered pests away
- Mulch: A thin layer of straw or hay over the seeds helps conceal them
- Timing: Planting in autumn reduces pest activity, as many birds are less active
When Is a Good Time to Seed?
As mentioned in our previous post, the best times to seed in the UK are September (early autumn) and April (spring). These seasons offer mild temperatures and regular rainfall, creating perfect conditions for germination.
The seed of fun!
Finally, a little humour to keep your spirits high while planting.
What’s a gardener’s favourite martial art?
Lawn-do!
Remember, planting grass is like making a cake. follow the recipe (or seed packet) carefully, and you’ll end up with something lovely to show off. Unlike a cake, though, your lawn won’t disappear at the next family party.
Happy planting, and may your grass grow greener on every side!