Whether you’re sowing a new lawn or overseeding an old one, you want to do it at the right time and in the right way. This guide will tell you everything you need to know.
When to sow grass seed – the short answer
When to plant grass seed in the UK – the long answer
Basically, you want to plant grass seed when there is warmth (but not excessive heat), plenty of sunshine and a decent amount of moisture. The reason why late summer to mid-autumn has the edge over mid-spring is because most weeds have already been and gone, so there will be less competition for resources.
The exception to this rule is if you want to plant grass seed under trees which shed their leaves as the grass seed will struggle to grow under the debris and if you clear up the debris, you’ll probably find yourself accidentally clearing up the grass seed as well. These areas are best done in the spring.
For the sake of completeness, if you have an area of really deep shade, then you’ll struggle to find any form of grass which will grow there, or anything else for that matter. In these locations you might want to go for either wood chips or some sort of decorative edging.
You never want to plant grass seed in winter or summer, because it will be either too cold or too hot and too dry and basically your grass seed is far more likely to shrivel and die than it is to grow.
How to sow grass seed
There are basically four steps to sowing grass seed. These are: choosing the right grass seed, preparing the lawn area, sowing the grass seeds and aftercare.
Let’s take a look at each of them.
Choosing the right grass seed
If you want to plant grass seed, then your first step is to choose the right grass seed for your area and your lifestyle. For your area, you’ll need to know your soil type (in particular the pH level and how well it drains), plus the local climate. For your lifestyle, think about now and in the future. If in doubt, sow grass seed which requires little maintenance, because it will still look better than high-maintenance grass seed which hasn’t been properly maintained.
Depending on the nature of your garden, you may want to plant different types of grass seed for different areas. For example, if part of your garden gets a lot of sunlight and another part is mostly in shade, then you might want to use different grass seeds for the different areas. Another possibility would be if one part of your garden gets a lot of traffic but the other part is mainly ornamental. Again, you might want to use different kinds of grass seed.
Pro tip, while you might think that “grass is grass” in actual fact when you see two types of grasses side by side, the difference between them can be very obvious. You could choose to make a feature of this or to blur the difference by using a combination of the two seed types over the part where the two areas join together.
Speaking of areas which join together, you can make your life a whole lot easier by keeping a hard border between lawns and beds, trees and ornaments. If nothing else, this means that you can do away with the edging shears and just mow right to the edge of your lawn area. You can also save yourself issues with roots causing damage to the edges of your lawn and also to foliage dropping onto your lawn and needing to be cleaned up quickly before it suffocates your grass.
Grass seed versus pathways
If you are using hard-wearing grass seed and doing everything properly and still finding that you regularly get bare patches in the same places on your lawn, then you should probably take this as a sign that the traffic is too much for any form of grass and that you either want to look at an alternative such as paving or at the very least give your lawn some help, for example, by putting down stepping stones.
Preparing the lawn area
Get rid of any surface debris and deal with any weeds. If you’re planning to use a residual weed killer and/or moss killer then you want to do so at least a month before you seed your lawn. This may seem like a long time, but you need every trace of the chemicals to be out of the soil before you sow your grass seeds, otherwise it will very probably kill them.
If you are going to use residual weed killer or moss killer, then it’s preferable to use one which also feeds your lawn as this will help to add the nutrients the grass seeds will need to grow.
Another trick beloved of experienced gardeners is to put a heavy covering over the ground, basically anything thick enough to block out all the light (it’s important that all light is blocked). Give it a few weeks and all the weeds will be dead and ready for removal.
If you’re overseeding an existing lawn (basically dealing with bare patches), it’s preferable to scarify the lawn thoroughly first. This will get rid of any thatch and remaining weeds (especially moss) which could suffocate your grass seeds.
Once you’ve scarified your lawn, or if you’re creating a new lawn dig over the earth with a fork if you can. If you can’t, then, as a minimum put a fork through it to aerate the soil. In either case, you want to get down to about 15cm.
Now would be a good time to make any adjustments. For example, you might need to add a soil improver or top soil, or if your soil is very sandy, you might want to add some lawn soil or sharp sand to help improve the drainage. Whatever you do, you want to end up with soil which is free of lumps.
Once this is all done, give the area a standard rake so that it is flat and then walk all over it so that the soil is compacted. Repeat and then finish with a rake to get rid of any footsteps or any other hollows which have formed and leave a perfectly flat surface. From this point on, you stay off the area until you are actually read to sow your grass seeds. Ideally, cover it with something which blocks out light completely to prevent weeds from taking hold.
A couple of days before you are ready to sow your grass seeds, rake in some lawn fertilizer to help get your grass seeds off to a good start. You may want or need to skip this step if you are using grass seeds which come with a fertilizer treatment, check the instructions on the packaging.
Sowing the grass seeds
Start by reading the instructions on the packaging and give them priority. For the most part, however, what you see on the packaging is likely to be a shortened version of the following instructions.
Divide the area to be seeded into segments. Try to make them as close to 1M by 1M as you possibly can the quantity of seed to use is generally given on this basis. An easy way to do this is to grab 4 garden canes and cut them to a metre each, you might also want to grab some stones to hold them in place. Alternatively you could use string, preferably coloured string, and again you’ll need something to hold it down.
Measure out the grass seeds properly. If you’re lucky, there will be a measure in the pack. If you’re not, you’ll need to find one or use scales. This is important as using too few seeds will obviously result in thin grass (if they survive) but using too many will lead to wastage as the excess seeds will not have room to germinate and so will just rot away.
Usually the packaging will tell you exactly how much grass seed to use, but if, for some reason, it doesn’t, here are the standard guidelines:
Grass seed for top-quality ornamental lawns : 30g per sq m (1oz per sq yd)
Grass seed for standard ornamental lawns: 20-25g per sq m (¾oz per sq yd)
Grass seed for standard utility lawns (with rye grass): 15-20g per sq m (½oz per sq yd)
Sow half the seed in one direction, turn 90 degrees and sow the other half of the seed. Then move on to the next segment.
When you’ve finished rake over the area so that the grass seeds are in the soil rather than just on the soil. Again, don’t overdo this as seeds also need light.
Ideally, you should finish by going over the area with a garden roller, but if you don’t have one, just walk over it, if possible put a cover down first, a plank will do or a tarpaulin, to give your seeds a bit of protection.
Water the seeds, again lightly.
Place fine-meshed netting over your seeded area to deter birds and for bonus points give your garden birds an alternative source of food which is easy for them to access. Advise the people in your life that they need to stay off the seeded area until it is properly established for which read about a month.
It’s really important to keep your soil moist, so if you don’t get rain, then you will need to water manually for at least the 7-10 days after sowing. Again, keep a light hand, use a manual watering can with a rose on or a hose gun with a mist spray (or a sprinkler with a mist setting).
Leave your grass to grow until it hits about 6-8cm and then, if possible, go over it gently with a garden roller. If that is not possible, then walk over it gently, basically you’re trying to compact the soil.
A couple of days later, mow off the top third (so down to 4-5cm), to encourage new growth. Don’t go crazy and scalp your lawn, it won’t be nearly strong enough to take this sort of treatment yet. If you have a cylinder mower, remove the front roller as it will be a bit too much at this point.
If you sow your grass seeds in spring, you’ll probably find that you get a lot of weeds in your lawn. You’re just going to have to ignore them for the first 6 months or so. There’s a good chance most of them will die back in the autumn in any case. If you sow in autumn, weeds are far less likely to be an issue, but if they do pop up then either ignore them or remove them by hand.
Resist any temptation to fertilize your lawn while it is becoming established (again, for the first six months or so). Overfeeding anything can damage it and in the case of new grass it can lead to areas looking burned. The exception to this is if the packaging specifically says that the grass seed needs to be fertilized, in which case follow the instructions.
How to plant grass seed FAQs
Here are some grass-seed related FAQs and the answers to them.
How long does it take to grow a lawn from seed?
Assuming good growing conditions, you should expect it to take about a month for you to have something which looks recognizably like a lawn. Basically allow up to 10 days for germination and then another 3 weeks or so for initial, slow, growth.
How long does grass seed take to germinate?
Very hard-wearing grass seeds may germinate in as little as 3-4 days but 7-10 days is more common.
How long does grass seed last?
In principle, if you store it properly, then good-quality grass seed can last for up to three years. That said, no matter how well you store grass seed, the quality will deteriorate over time, meaning fewer seeds will germinate. This means that, in practice, you should really aim to use up grass seed within one year.