If your plans to plant a new lawn were delayed or you kept back 5 to 10 pounds of seed to use to fill in gaps, you’re going to want to know the shelf life of grass seed and how to store those seeds properly. The difference between the grass seed shelf life for seeds that have been stored properly compared to seeds that were left in poor conditions is drastic.
How Long Does Grass Seed Last? (The Short Answer)
How long does grass seed last with a decent germination rate? 3 years, if those seeds have been stored properly. Seeds that have been allowed to sprout or freeze should immediately be considered non-viable. Keep in mind, however, that even seeds kept in the best conditions will not retain their stated germination rate for more than 12 months.
Does Grass Seed Go Bad? (What Happens to It Over Time)
Like any other type of seed or natural product, grass seed will go bad or deteriorate given the right conditions or enough time. In short, grass seeds expend energy and resources slowly over time. Eventually, they will no longer have what they need to germinate or grow successfully.
Even seeds that can successfully germinate may have accrued enough damage over time that the plants they produce will be stunted or appear “off” in some way. Seeds collected from these damaged plants, if they can mature, will often still produce plants that are “off” in some way or these seeds may not be viable.
Membrane Degradation and Loss
When a seed starts to go bad, the first thing it will lose is its protective membrane. Without this, it will have a hard time regulating the moisture content of the seed and becomes susceptible to bacterial or fungal infection as well as the drying effects of the air. Storage in a sterile, air-tight container can help solve these issues.
Loss of Energy Storage and Synthesis – Impaired Respiration
Once the membrane has degraded, the next thing that happens is a slow loss of the seeds’ ability to retain stored energy and to create or synthesize the energy needed to properly germinate. With time this results in a greatly reduced possibility of germination and, if germination does happen, it will be much slower than it should.
Abnormal Development
As these important energy-production and storage mechanisms are impaired, the seed may become damaged in a way that impacts its uniformity, yield, and overall appearance and function once it does become a plant.
This may mean a plant that appears stunted, has misshapen leaves, or fails to flower, fruit, or bear viable seeds. Once enough damage has been accrued, the seed will simply fail to germinate at all.
Loss of Viability
Seeds that are no longer viable often appear lighter in both weight and color. They may smell musty or “stale” even when everything else appears normal.
Factors That Affect the “Shelf Life” of Grass Seeds
Given that grass seeds are somewhat fragile and even seed storage banks have not kept more than a handful of varieties for longer than 5 years with any acceptable degree of success, 5 years is the maximum amount of time you should expect to keep your grass seed viable in any way. That is if you keep those seeds under ideal conditions.
Under normal circumstances, however, I would not use seeds that are more than 3 years old, if stored properly. If your seeds have encountered several of the factors below, it may be best to replace them altogether.
Humidity and Moisture Content
The most important factor in maintaining the shelf life of grass seeds is keeping the humidity and moisture of the seeds under control. Humidity is half of “the 100 rule”. This rule is simple and relies on the fact that, above freezing, the lower the temperature is, the higher the humidity can be without damaging your seeds.
For example, if your seeds are stored at 40F, humidity can be 60% while if your seeds are stored at 70F the relative humidity should be no higher than 30% as 40+60=100 just as 70+30=100.
Humidity that is too high at a high temperature can cause your seeds to germinate in their containers. Humidity that is too high at low temperatures can cause rot, if those temperatures are above freezing, or can crystallize and destroy a seed from the inside, in the case of freezing temperatures.
Temperature
Can grass seed go bad if it is frozen? Yes. However, freezing isn’t the worst way to store grass seeds. The deciding factor for whether or not freezing will harm your seeds is humidity. If you carefully remove as much excess moisture from your seeds as you can before freezing, and you keep them frozen until you need to use them, you could extend their viable life by about 6 to 8 months.
This short length of time, however, is often not worth the trouble. Beyond freezing, temperatures that are too high rarely cause problems as long as humidity is low.
Pests and Sanitation
When does grass seed go bad when it’s been exposed to rodent or insect damage? Rapidly. Not only do mice and insects physically destroy or consume seeds but they indicate a problem in the storage zone or container as well as introduce your seeds to harmful bacteria and even carry fungal spores in with them.
If you notice insects crawling in your grass seed or evidence of rodents and are unsure when contact occurred, these seeds are probably already non-viable or well on their way to being.
Variety
How long does grass seed last when it’s X variety? This is an important question to ask. Hybrids and types of lawn grass, in particular anything with “annual” in its name, will only last about 2 years no matter how they are stored.
Grasses that are closer to their “natural” variant or that are meant to last through a freeze-thaw cycle such as buffalo grass or perennial ryegrass will hold out for closer to that 5-year maximum.
Tall fescue seeds, however, are short-lived and are hard to keep viable for more than 2 years in the best conditions.
Seed Quality
One factor that is often overlooked when it comes to grass seed shelf life is the state of the seeds at harvest. While it is nearly impossible to know this if you are picking up a commercially available product, when the seeds were harvested during their life cycle can greatly affect their shelf life as well as what they produce when they are planted.
Method of Storage and Container
Can grass seed go bad if left in the open or not in a container? Yes. Grass seeds should be stored in a sterile, air-tight container. This helps insulate them from spores, bacteria, and pests as well as fluctuations in temperature and humidity.
How to Know if Your Grass Seed Had Gone Bad
While it can be difficult to tell if grass seeds have gone bad entirely or if they are still somewhat viable with just a glance, there are a few factors that can tip you off. If you want to be more certain, however, we also have an article on how to tell if grass seed is still good that includes a simple and much more conclusive test.
- Color – Grass seed that is significantly paler than when it was first opened has likely gone bad.
- Weight – Grass seed that has gone bad will be significantly lighter than it was when stored.
- Smell – Grass seeds that have “expired” will often smell musty or stale, in my experience.
- Package Date – Does grass seed expire by the date printed on the package? Very few seed packages have a printed-on expiration date and this date can typically be ignored if your seeds have been stored well. Most often the date you will find printed on the packaging of your grass seeds will be either a harvest date or a packaging date. It’s usually safe to use this date as the starting point for any calculations about grass seed shelf life. If stored properly, your grass seed should be fine for about 12 to 18 months from this date.
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