How Long Can Grass Seed Be Stored? Does It Go Bad?

If you’ve ever ended up purchasing way too much grass seed, you’ve probably also wondered if it’s possible to store it. 

Additionally, there’s a good chance you’re curious about exactly how long you’ll be able to safely store the seeds without them becoming moldy, expired, or otherwise damaged over time.

If kept cool and dry at all times in an area with decent airflow, it is safe to store grass seed in a sealed plastic container or bag for up to two years. Ideally, it should be stored at around 40-50° degrees Fahrenheit (10° C) with a desiccant to prevent moisture from forming and causing germination or mold growth.

Read on to go over everything you need to know about the perfect conditions to maximize your grass seed’s longevity and quality, so it doesn’t go to waste!

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How Should You Store Grass Seed?

The best way to store grass seed is in an airtight plastic storage container or a very thick, sealed plastic bag. It should be kept in a dry, cool area with consistent airflow at no warmer than 50° degrees Fahrenheit (10° C). Use a desiccant in the container to prevent moisture from forming.

When storing grass seed for an extended period, your main goal should be to keep the seeds (as well as the storage environment) dry. 

If they come in contact with any moisture, you’ll end up with partially germinated seeds or, worse, mold or fungi-covered seeds, which will be unusable later and make the entire process of storing them useless.

In addition to keeping the stored seeds dry, they should also be kept in a cool and dark room. 

The air temperature should ideally be within 40-50° degrees Fahrenheit (10° C), though slight fluctuations are okay from time to time as long as no moisture is introduced to the seeds. 

The room should have consistent and adequate airflow, even though the seeds themselves will be stored in an airtight, sealed container.

If you’re planning to store the grass seeds for several months or more, be sure to clearly label the container with the type of seeds and the date you initially stored them. 

Large plastic or metal storage containers are both an excellent choice to prevent rodents and other pests from accessing them. 

As far as desiccants go, an open box of baking soda placed in the bag of seeds is a convenient and inexpensive choice. Silica gel packs are also ideal.

How Long Can Grass Seed Be Stored?

If it is stored in a cool, dry area and no moisture has gotten inside, it can store grass seed for one to two years after its initial testing date. You’ll be able to use the seeds after this point, but the germination rate drops after about 15 to 18 months, even in ideal conditions.

There’s a lot of debate within the gardening and lawn care communities regarding exactly how long you’ll be able to safely store (and later use) grass seed. 

Some sources claim their grass seed stays fresh for as long as three years in optimal conditions, while others warn to only store seeds for a little over a year at most.

The main reasons for this are the significant variations in how people store their seeds, the type, and quality of seeds used, and the conditions the seeds, are stored in. 

In addition to this, the germination rate of most seeds slowly decreases over time as they are stored, even in a perfectly sealed container in a cool, dark room with decent airflow. 

After about 12 to 18 months, the percentage of seeds that will properly germinate in a typical bag or container starts to drop pretty significantly. 

This rate only increases if the seeds are not stored in cool and dry conditions, such as if the temperature becomes too warm or moisture buildup ends up getting into the container the seeds are stored in.

It’s best to store your grass seed for no more than a year if you want to ensure the highest germination rate once you eventually plant them. 

However, it is possible to store them for as long as two years with minimal impact on the seed viability, as most seeds have a reasonably long shelf life due to their hardiness.

How Long Can Grass Seed Be Stored And Still Be Germinated?

Ideally, you should store your grass seed for a year or less if you want to ensure a high germination rate when you plant them later. While it’s possible to store certain types of grass seed for as long as three years, their germination rate drops significantly over time after the one-year mark.

A good rule of thumb to follow when storing grass seed is to only store it for a year and a half at most to ensure the highest possible germination rate. 

After the first year or so of storage, germination rates of most types of grass seed tend to start dropping pretty drastically, even by as much as 20% each subsequent year.

This means if you don’t want to end up potentially wasting a significant amount of grass seeds when it comes time to plant them later, you shouldn’t store them for more than a year. 

Even if you’ve taken every possible measure to ensure ideal storage conditions, the rate will still naturally drop on its own without any intervention from you, common pests, or the elements.

If the germination rate isn’t necessary to you and you don’t mind the possibility of 10% to 30% of your seeds not sprouting, it’s possible to safely store the seeds for as long as three years. 

At this point, most of the seeds will still be viable, or at least around 75% to 80%, provided you’ve kept them stored in cool, dark conditions away from rodents or other pests.

After the three-year mark, though, the seeds’ viability will begin dropping even more significantly each year, so it’s best to use them within a year of their testing date, regardless of the type of seed. 

A few documented cases of even 20-year-old expired seeds germinating, but this is extremely rare and unlikely.

How Do You Know If Grass Seed Is Still Good?

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To determine if your grass seeds are still viable, put a few of them in a cup with a couple of inches of water. Leave the seeds to sit in the water for 10 to 15 minutes. If they sink to the bottom of the cup, the seeds are likely still usable. If they float, they probably won’t germinate properly.

You usually won’t be able to tell just by looking at your seeds if they can still germinate. 

Of course, if pests have ravaged them or you notice any signs of fungi or other mold growth, you’ll have your answer, but if they look fine at a glance, it’s often a bit harder to determine if they’re viable.

First, ask yourself how long the seeds have been stored. 

If you’ve stored them for less than a year and the reasonably fresh seed hasn’t been damaged by moisture or pests, chances are, they’re still perfectly viable. 

However, if you don’t know how long the seeds have been stored for, they’re probably a good candidate for what’s known as the “water test.”

This simple water test is a great way to determine if a sample of seeds can still germinate properly. 

Be sure to use a good sample from somewhere in the middle of the bag or container where you’ve stored them rather than using the seeds directly on top, as the seeds on top are more susceptible to being damaged over time.

A small handful of 5 to 10 seeds is plenty when it comes to determining if the bag they’ve come from is viable for planting later. 

Fill up a cup of water with 3-4″ inches of water, and then simply place the seeds into the cup.

Leave the seeds alone for at least 10 to 15 minutes, and then come back to check on them when time’s up. 

If all of the seeds have sunk to the bottom of the cup, then they’re still viable and safe to plant. 

If they’re floating on the surface, though, this means they likely won’t germinate appropriately if you plant them.

If some of the seeds are floating and some have sunk, it’s up to you whether you want to use them or not. 

The germination rate is probably not great for them, though, so it might be more worth your time and money to simply buy new, quality seed.

Does Grass Seed Go Bad In The Bag?

If unopened and stored in the right conditions, a sealed bag of grass seed will stay viable for as long as three years. If the bag has already been opened, the seeds might have already started to go bad. Conduct the floating water test on a sample of seeds to tell if they are still viable.

The original packaging your grass seed was sold in isn’t designed to be stored for very long periods. 

However, if it is left unopened and sealed correctly and is stored in cool, dark conditions away from direct sunlight in a room with adequate airflow, the seeds can stay viable for as long as three years!

Unfortunately, this isn’t always the case, as it depends on many external factors often beyond your control. 

Even the most high-quality seeds will only stay good for around one year on average to two years at most. 

Rather than storing the seeds in the bag they were initially purchased, empty them into a more sturdy and airtight container. 

The bag you bought the seeds in isn’t designed to last or protect the seeds for very long periods, so it’s best to keep them somewhere more reliable in the long term, especially if you won’t be able to plant them for another year or so.

Otherwise, don’t count on the seeds to stay viable for more than a few months at most if you just keep them in the bag and attempt to re-seal them on your own. 

The seeds will be especially prone to mold, rodents, other pests, and fungi if kept in an unsealed bag for a long period.

Can Grass Seed Be Stored In A Garage?

It’s best to keep grass seed indoors in a temperature and moisture-controlled room around 50° degrees Fahrenheit (10° C) rather than a garage or shed, as these areas often become very moist and hot during the warmer seasons (depending on where you live). Excess moisture and heat will damage the seeds significantly over time.

While it might seem natural to keep your fresh grass seed stored in your garage, you should instead store it indoors in a very cool and dry area. 

If your garage happens to have air conditioning and isn’t particularly prone to moisture, then great, but most are hotspots for mold growth and warm temperatures.

The same rule also applies to most storage sheds. If you’re able to keep your shed cool and dry, the seeds will be fine, but in all likelihood, proper storage won’t be possible. 

Keep the seeds stored in an airtight container, made from thick plastic or metal. 

Keep the container stored at around 50° degrees Fahrenheit or in the coolest location possible to ensure the seeds’ longevity and a high germination rate.

Does Grass Seed Go Bad If It Freezes?

It is safe to store grass seed for up to two months in freezing temperatures below 32° degrees Fahrenheit (0° C), but it isn’t great for them in the long term. When the seeds thaw, they will become moist, so you should plan to plant them immediately after thawing if you freeze them.

Grass seed generally won’t go bad if frozen for short periods. 

Just be sure to avoid freezing any seeds for longer than two months. 

Even though most types of grass seed are fairly hardy, their germination rates have a chance of dropping if temperatures fluctuate too much or too quickly.

If you do freeze your leftover seed or your seeds happen to become frozen through some circumstances you aren’t able to control, opt to plant them as soon as possible after they thaw. 

If you aren’t sure if they’re still viable, take a sample of the seeds and do a quick water test and see if they float or sink.

Check out our full guide on how long grass seed takes to grow for tips and answers on growing your lawn.