If your lawn looks tired and tatty and is covered in weeds, moss and bare patches, it might be time to bite the bullet and sow a new one.

The advantage of sowing a lawn from seed is obviously the cost - it is much cheaper to sow seed than to buy turves which may not be the exact quality you want and will also deteriorate rapidly if they are not laid as soon as you have bought them.

You can also pick your day to sow. It doesn't matter if the weather suddenly turns frosty - you can just wait for it to warm up a bit. There is more of an urgency if you buy turf - and if you are having it laid for you, you can't pick and choose your day.

With lawn seed, you can also select a number of different grasses which will be suitable for particular areas of your garden. If you have children you are likely to need a tougher variety than if you just want a velvety lawn which is rarely set foot upon.

But remember that there is no point in buying a very fine grade unless you are prepared to cut it at least twice a week, feed it, water it and give it all the TLC it needs.

Growing a lawn from seed requires much initial preparation of the soil. It is hard work, but it will be worth it in the end.

You will need to dig the ground over thoroughly, to a spade's depth. If you have a really big area to sow, it may be worth hiring a rotavator, but make sure you get rid of all the weeds beforehand. Otherwise, a rotavator will simply chop up running roots which will then spread, encouraging weeds to spring up all over the place.

If you have very heavy clay soil, lighten it with grit, which you need to dig in. Rotted manure or compost should be added to light soil to give it some substance. You can level minor humps and bumps as you go, but if the site is seriously uneven, you'll need to remove the topsoil and stack it somewhere, level off the subsoil and then replace the topsoil layer.

Remember when digging that the clods need to be broken down or your lawn will end up uneven. Trample roughly dug earth with your feet and break up hard clods with the back of your garden fork.

One of the most important jobs when sowing a new lawn is to consolidate the soil, firming the site as you go. Walk in overlapping steps, treading over the whole area with your heels, before sprinkling on a general fertiliser such as blood, fish and bone or a special lawn fertiliser. You need to choose a day when the soil is fairly dry and not sticking to your boots.

Finally, rake over the area and remove any remaining stones and debris, making sure that the surface level is firm, with no soft spots that will sink later. The surface should have a fine, crumbly texture. You may have to go over it a few times before it is how you want it.

Once the soil is prepared, you are ready to sow. It is, in fact, best to sow in late summer or early autumn, when the ground is still moist, but April is also a good time, provided you don't do it during an excessively dry spell. Sow at around 50g per square metre and if you are unsure, practise first on a sheet of paper on the garage floor, marking the area into metre squares with canes and string.

The late, great gardener Geoff Hamilton recommended an easier way of sprinkling the right amount of seed into a set area - stand with your feet wide apart, lean forward as far as you can go and that's about a square metre.

Sprinkle two handfuls of seed over the area you are covering and that should be about the right amount.

Once you have scattered the seed, rake it in with a spring-tine lawn rake - don't try to bury the seed or germination will be patchy - and then water if it doesn't rain within 24 hours. Try to use your finest rose on your watering can or sprinkler, though, or it will wash the seed into patches.

You will also need to protect the new lawn from birds, which are prone to using the seed bed as a dust bath. Put up some posts with flapping strips of plastic attached to frighten them off.

Seedlings should appear two to three weeks after sowing, and when the grass is two or three inches high, roll it lightly using the back roller of a cylinder mower with the cutting head held high. This firms down the soil lifted by the seedlings and encourages them to produce new shoots.

After another few days, the lawn can be mown very lightly with the cutting blade at its highest. Make sure your mower blades are sharp. Don't cut the grass too closely in the first year and make sure it receives plenty of water when necessary - and try not to let the kids run riot in the first 12 months after sowing.