Grass seed is an important product for homeowners, landscapers, golf courses, parks departments, and others who need to establish turfgrass. When freezing temperatures occur, questions often arise about whether grass seed that has been exposed to the cold is still viable and able to germinate and grow. This article will examine whether grass seed can withstand freezing and what factors influence its ability to still be usable after exposure to below-freezing temperatures.
Quick answers
– Grass seed can freeze and still germinate, depending on factors like moisture content, temperature, duration of freezing, seed variety, and more.
– High moisture content makes grass seed more susceptible to damage from freezing. Keeping seed dry helps protect viability.
– The colder the temperature and longer the duration of freezing, the more likely damage will occur. Brief freezes just below 32°F are less risky than sustained deep freezes.
– Some grass seed varieties are more cold hardy than others when it comes to freezing. Fine fescues, for example, tolerate freezing better than some warm season grasses.
– Frozen grass seed should be thawed gradually before planting. Do not plant frozen seed.
– Grass seed that has been frozen should be tested for germination rates to determine viability before large-scale planting.
Does grass seed die if frozen?
Grass seed usually does not die immediately when exposed to freezing temperatures. However, frozen grass seed is susceptible to damage that can affect its ability to germinate. The level of damage depends on several key factors:
– Moisture content – Grass seed stored in a dry state can withstand freezing better than seed with high moisture content. Wet or damp seed is more prone to injury from ice crystal formation during freezing.
– Temperature – The colder the temperature, the higher risk of damage. Temperatures below 20°F can impair vigor. Hard freezes below 0°F are especially detrimental. Brief freezes just below the 32°F freezing point are less harmful than sustained deep freezes.
– Duration – The longer grass seed remains frozen, the greater the cumulative effects. Seed frozen for a few hours or single night is less at risk than seed frozen for multiple days or weeks.
– Seed variety – Some grass cultivars and species have greater freezing tolerance based on genetics and adaptations. Fine fescues, for example, tend to withstand freezing better than some warm season grass varieties.
– Age of seed – New crop, recently harvested grass seed typically has higher vigor and is more resilient to freezing stress. Older seed batches are usually more vulnerable.
The combination of these factors impact whether freezing will kill grass seed or just damage its growth potential and percentage of germination. Freezing alone does not necessarily kill grass seed, but it becomes a numbers game of how many seeds from a frozen batch will still be viable.
Does frozen grass seed still grow?
Frozen grass seed can potentially still grow and germinate after thawing, but its germination rate will likely be diminished. The ability of frozen seed to still be viable depends largely on:
1. Degree of damage from freezing – The less injured from ice crystals, the better change of germinating.
2. Thawing process – Gradual thawing in a refrigerator is better than fast thawing at room temperature.
3. Seed treatment – Priming seeds via soaking in water for rehydration can aid recovery.
4. Seed viability to begin with – Higher quality, newer crop seed withstands freezing stress better.
5. Germination testing – Check germination rate on a sample before large planting.
Ideally, grass seed should be stored in a dry, controlled environment to prevent freezing. But if seed does become frozen, it can possibly still grow if damage was minimal and it is handled properly after thawing. The germination rate is likely to be lower than unfrozen seed. Vigor may be reduced, but frozen seed is not necessarily dead seed.
Germination rates of frozen grass seed
When testing grass seed viability after freezing, germination percentage is a key measure. University research has documented how germination rates are impacted by freezing based on temperature and duration:
– Tall fescue seedstored at 0°Ffor 3 months – 79% germination
– Tall fescue seed stored at -4°F for 3 months – 71% germination
– Perennial ryegrass stored at -4°F for 3 months – 42% germination
– Creeping bentgrass seed at -4°F for 6 months – 15% germination
– Annual ryegrass at -4°F for 1 month – 64% germination
– Annual ryegrass at -4°F for 3 months – 20% germination
These studies show germination falls significantly the colder and longer grass seed is frozen. But even seed stored constantly below 0°F retains some viability.
Research at University of Rhode Island found that a non-treated control of tall fescue seed had 85% germination after being frozen at -4°F for 56 days. Priming the seed by soaking in water for rehydration prior to freezing boosted germination to 91% despite the subzero temperatures.
So testing will reveal that even badly frozen grass seed can have decent germination rates. The testing also quantifies how much additional seed should be planted to account for reduced germination.
Thawing and handling frozen grass seed
For best results with frozen grass seed:
– Allow gradual thawing – Move seed in sealed containers from freezer to refrigerator to thaw slowly. Avoid fast thawing at room temperature.
– Test germination rate – On a sample to determine how much extra seed will need to be sown.
– Rehydrate seed – Priming in water for several hours can aid recovery.
– Sow seed heavier – Due to reduced germination, increase seeding rate 15-25% or more.
– Check seedlings – The stand may be thinner so reseed any bare spots.
When rehydrating and germination testing after freezing, the goal is to minimize further stresses and restore vigor. Handling and planting frozen seed should focus on recovery. With extra care and heavier seeding rates, previously frozen seed can still produce an acceptable stand of grass.
Grass species and freezing tolerance
When evaluating grass seed viability after freezing, the species itself matters. Some common cool season turfgrass species are more cold hardy than others:
More tolerant:
– Fine fescues
– Kentucky bluegrass
– Perennial ryegrass
Less tolerant:
– Tall fescue
– Annual ryegrass
Among warm season grasses, bermudagrass is more freezing tolerant than zoysiagrass, buffalograss or centipedegrass. Bahiagrass, carpetgrass and St. Augustinegrass are prone to winter kill.
Research specifically on hardiness of frozen grass seed is limited. But field observations and experience align with the list above of relative cold tolerance. When exposed to freezing, fine fescue seed would likely suffer less damage than annual ryegrass seed, for example.
Seed producers focus freezing tolerance breeding efforts on fruits, vegetables and grain crops more than grasses. But enhancements in cold hardiness of turfgrass cultivars continue through natural selection and hybridization, benefiting their seed as well.
Protecting grass seed from freezing
While grass seed can potentially withstand freezing temperatures and still germinate, preventing seed from freezing in the first place is wise. Here are tips for protecting seed:
– Store in a controlled dry environment
– Insure proper drying after harvesting
– Use moisture-proof sealed containers
– Keep seed in interior spaces above freezing
– Avoid temperature fluctuations
– Prevent condensation on containers
– Limit duration of outdoor exposure
– Handle with cold chain management
– Distribute seed early before ground freezes
– Keep seed dry when sown in late fall
Grass seed preserved under ideal storage conditions and protected from freezing will have consistently higher germination rates. For best results, proactive measures to prevent freezing damage makes more sense than trying to plant seed later that has been subjected to cold temperatures.
Testing frozen grass seed viability
Determining the viability of grass seed after exposure to freezing is recommended, either for inventory management or if unintentional freezing occurs. Options for testing include:
– Standard germination test – Follow Rules for Testing Seeds procedures
– Tetrazolium chloride test – Assess cellular living tissue
– Electrical conductivity test – Measures leakage from damaged membranes
– Accelerated aging test – Simulates further deterioration
– Seedling evaluation – Grow-out trial for visual quality analysis
While testing takes time and resources, it provides valuable data. Inventory can be adjusted based on actual germination rates. Higher seeding rates can compensate for substandard viability if planting frozen seed. Testing helps determine if re-seeding is necessary after emergence of a thin stand.
Proper sampling, testing procedures, and interpretation of results are key. Consult with accredited seed analysts and turfgrass specialists when evaluating frozen seed.
Buying grass seed that has been frozen
Purchasing “carryover” grass seed that has been frozen from year to year is an important consideration:
– Ask suppliers about original quality – Higher vigor seed withstands freezing stress better.
– Inquire about conditions during freezing – Constant subzero temperatures impact viability much more than fluctuating above and below freezing.
– Request germination test results – Any reputable seller should be able to document up-to-date test findings.
– Compare pricing – Account for needed higher seeding rates by adjusting the cost/benefit analysis.
– Plan swift distribution – Don’t leave purchased frozen seed outside exposed to further freezing.
– Be prepared if results disappoint – Have backup seed source rather than relying solely on questionable inventory.
– Consider seed treatments – Priming or coating may help compensate for weakened vigor.
With proper research and realistic expectations, grass seed frozen for a limited period can still produce an acceptable lawn or turf stand. But extra diligence is required when sourcing, testing and planting previously frozen seed.
Conclusion
Freezing temperatures do not automatically kill grass seed. But frozen seed suffers cumulative damage the longer and colder it remains frozen. Lower germination rates are likely after freezing. With care in thawing, testing, seed treatments and planting, frozen grass seed can still grow but higher seeding rates may be needed. Certain species and newer crop seed better tolerate freezing stress. Whenever possible, proactively storing seed dry under controlled temperatures is ideal to prevent freezing damage and retain optimum germination rates. But understanding treatment of previously frozen seed can still help achieve reasonable results, usually with more seed required per area.
