How Long Does Grass Seed Last?

Open hand with grass seed for reseeding the lawn.

Does your lawn need reseeding or are you ready to plant a new lawn on your property? If you are going to grow new grass, you will need to invest in grass seed. Before you get started on your landscaping project, you may have some questions about using old grass seed and you may wonder how long does grass seed last. Here is what you need to know about purchasing, storing and using grass seed, including learning how long grass seed is good for use.

Grass seed comes in a variety of types and usually is sold in plastic bags at your local garden or home center. These bags of grass seed are ready to plant, but not all the seeds may produce new blades of grass. Germination rates are an important factor to consider when buying and storing grass seed – this rate can impact how long grass seed is good and how effective it will be when planted. Quality grass seed will have an expected germination rate advertised on the bag that should be accurate during the first year after harvest.

How Does Grass Seed Age?

Believe it or not, grass seed changes over time. Newly harvested grass seed that is properly harvested and stored has a very high germination rate – most of the seeds will produce new grass. A new batch of grass seed may have an 80% or higher germination rate, meaning 80% of the seeds will produce grass. However, as grass seed ages, this rate decreases. Even in optimum conditions, grass seed will lose 10% of its germination rate each year.

When you buy grass seed, there should be an expiration or “purchase by” date. This date does not mean the grass is no longer viable, but it does tell you how soon it should be used to get the highest germination effect. If you are planting a new lawn, this is important. You want to ensure that you have a higher germination rate with the grass seeds you use to get a thick, even lawn. If the grass seed you own expired a few years ago, the germination rate has decreased by 20% or more, impacting the effectiveness of your seed.

Ideal Storage for Grass Seed

How long does grass seed last? It depends on how it is stored. While grass seed will decrease in germination rate each year it is kept, it can still be used for reseeding your lawn if it is stored correctly. Grass seeds can last for many years, but you can expect to need to use more to produce the same amount of grass. It is important to ensure the seeds are stored in a cool, dry place and sealed away from rodents.

Ideal storage for grass includes a sealed container that will keep out moisture and light. Grass seed is susceptible to fungus and mold from moisture, which can ruin your grass seed. Plus, light and moisture can allow seed to sprout, which will reduce the germination rate even further. A sealed container kept in a garage or cool place is best – seeds should not be kept in outdoor sheds if temperatures will go below freezing.

Plastic bag with grass seed that is going to be used for reseeding the lawn.

How Long is Grass Seed Good to Use?

When it comes to using grass seed for planting a new lawn, you want the best quality to achieve a thick lawn. It is best to buy new, quality seed for a new lawn to get the best results. If you have leftover seed, you can store it using the previous methods for overseeding your lawn. While the germination rate will lower with time, your grass seed should last for two or three years if it is kept dry and sealed away from rodents.

If you have grass seed that has been stored properly, but you are not sure if it is still good, you can test its germination. Take 10 seeds from the batch and put them on a damp paper towel and seal in a plastic bag. Set the bag in a warm, lighted area and allow them to grow. In two weeks, you can check how many seeds sprout – that will tell you your germination rate. Four sprouting would be 40%, five sprouting is 50% and so on. If only one or two sprout or none sprout, your seed is no longer viable for planting.

How long does grass seed last? You now know that depends on how you store it and for how long.

To get the best results when planting a lawn or even overseeding, you should use quality grass seed that is within its first year after harvest. Ask you local landscape supplier for a quality brand of grass seed that provides the harvest or test date to ensure your new seed is fresh. To keep leftover seeds, make sure you store it correctly to get the best results when you use it next year.