It’s Too Cold for Grass Seed

The weather can be deceiving and tempt you into planting at the wrong time. Spring and autumn temperatures can be warm by day but drop down to near freezing at night. This means the soil temperature may be quite cold.

If you've been watering or it’s been raining, then this will reduce the soil temperature even more, exacerbating the problem. Shady areas will also have a lower temperature.

This means taking temperature, weather and location into account when deciding if it is warm enough to plant grass seed. An average day night temperature of at least 8 degrees but nearer 12 degrees should be your target. For example a spring night temperature may be 2 degrees with a day temp of 14 degrees. This is going to give you an 8 degree average which is not ideal so wait for warmer weather.

You let the Grass Seed Dry Out

In the article All about Grass Seed Germination you will get an understanding of the importance of constant moisture. If therefore you water, let it dry, water again and so on then the seed never gets to the point of germinating. The golden rule is NEVER LET SEED DRY OUT. 

It's too Dry

Dry springs are becoming more and more common meaning little moisture in the soil by the time you come to plant your seed in soil at the correct temperature. Keeping seed moist under these conditions is an uphill battle so if you haven't built a reservoir of moisture in the soil by watering for a few days before seeding then it is virtually impossibly to prevent the seed from drying out with frequent daily light watering. The best way to combat dry springs and/or cool soil temperature is to build a reservoir of moisture, plant the seed and incubate under polythene sheeting. This prevents evaporation, warms the seed, keeps it moist and protects from birds and the elements.

Thatch, Moss or Debris remains after Scarifying or Raking

When over seeding the seed must contact the soil. Any vegetative debris that remains puts a barrier between the seed and the moist soil. The seed germinates and the little root shoot that emerges can't get to the soil and dries out and dies. You need to seed onto bare soil at all times.

Compaction

This is only applicable if the soil has not been dug so occurs if seeding bare patches or scarifying existing lawns. Compaction prevents the soil holding water and air required by roots to develop. In addition if the soil surface is hard baby root shoots may not be able to penetrate.

Planting Grass Seed too Deep or Using Top-Dressing

Grass seed needs to be on the surface and no more than 2-3mm deep. It also needs to be in good contact with the soil by either treading in or lightly rolling. Plant it too deep or cover it with more than a very thin layer of soil or top dressing and you may well stop it germinating.

The Grass Seed is Too Wet

Being too enthusiastic with watering particularly on clay soils that easily water log can also cause problems as the seed once germinated needs oxygen to survive. Water logged soil means it will drown. 

Do not Cover Grass Seed with Peat or Compost

If repairing patches people sometimes cover it with peat or compost. Unfortunately, if it dries out it will actually draw moisture away from the seed preventing germination or growth.

Seed is Old

This is most unusual as grass will keep for several years and still have reasonable viability. The way it is stored is usually the cause of poor germination in seed older than a few months.

Stored Incorrectly

High temperatures, humidity, light and sweating are the biggest seed killers.

Storing in a cool dark area of a basement or garage are probably the best places though basements can be humid. Away from light is easy so the main aim then is to keep the grass seed dry and cool. Garden sheds get very hot and this can easily ruin your seed in days. If you have an old fridge and not much seed to store this would be perfect.