Fertilizing dormant grass is a debated topic among lawn care experts. While some argue that fertilizer applied in fall or winter is wasted, others claim that fertilizing dormant grass provides nutrients that prepare the lawn for vigorous spring growth. Understanding the pros and cons can help you decide if fertilizing dormant grass is right for your lawn.
Quick Answers
Here are quick answers to common questions about fertilizing dormant grass:
Is it a waste to fertilize dormant grass?
Not necessarily. Nitrogen applied in fall or winter can leach down into the soil and be available for root uptake in early spring. However, much of the nitrogen may be lost to leaching or volatilization during extended dormancy periods.
When is the best time to fertilize dormant grass?
Late fall is optimum, as the grass plant will absorb nutrients to store energy reserves before going dormant. Fertilizing in winter is less effective but can still provide some benefit.
What kind of fertilizer is best for dormant grass?
A balanced slow-release nitrogen fertilizer is ideal, as it will break down gradually over time. Quick-release fertilizers applied during dormancy are more likely to leach out of the root zone.
Should iron be applied to dormant grass?
Yes, iron provides an important nutrient and green-up benefit for dormant cool-season grasses. Iron is more readily absorbed by grass plants in cool weather.
Does fertilizing dormant grass increase growth?
Yes, proper fertilization in fall and winter results in healthier, greener, and thicker turf in spring. However, dramatic growth flushes should be avoided during dormancy.
The Dormancy Period
Cool-season grasses like fescue, bluegrass, and ryegrass naturally go dormant as temperatures drop and daylight hours decrease in fall and winter. Growth slows down dramatically, and the grass turns brown and stops growing. However, the plants are still alive, and the crowns, roots, and rhizomes remain active over the winter months.
Warm-season grasses like zoysia, Bermuda, and St. Augustine also go dormant each winter. Their dormancy period is much shorter though, as warm-season grasses only remain dormant when temperatures drop below 55°F for extended periods.
The dormancy period varies depending on grass type and climate. Where winters are mild, grasses may only lose their green color for a few weeks. In cold climates, dormancy can last 4-6 months before the grass greens up again in spring.
Pros of Fertilizing Dormant Grass
Here are some potential benefits of fertilizing grass in fall and winter while it is dormant:
Nutrients Are Available in Spring
Nitrogen and other nutrients applied during dormancy can leach down into the soil profile where they are held in reserve. As soil temperatures increase in spring, the roots begin actively absorbing nutrients and energy stored in the crowns is mobilized for greenup and growth. Having readily available nutrients helps the grass bounce back quickly and vigorously.
Strengthens Roots
Phosphorus and potassium applied during dormancy are especially helpful for developing robust root systems. Stronger roots improve heat and drought tolerance in summer.
Improves Winter Hardiness
Fertilizing grass plants in fall helps them store more energy reserves in the form of carbohydrates and sugars. The increased energy fuels growth when conditions improve and helps the grass recover from winter injury.
Greener Turf in Spring
Nitrogen applied in late fall or early winter results in earlier spring green-up. The flush of growth caused by the fertilizer minimizes the yellow look of dormant grass. Iron sources in winter fertilizer also enhance the green color.
Thicker Turf in Spring
Applying nitrogen in fall and winter nourishes the crowns, stems, and roots of grass plants. This leads to new shoot and tiller development for a thicker lawn after spring growth resumes. Dense grass crowds out weeds.
Cons of Fertilizing Dormant Grass
Here are some potential drawbacks of fertilizing dormant grass:
Nutrient Leaching
Since grass plants are not actively growing and absorbing nutrients during dormancy, applied fertilizer is more prone to leaching. Soluble nitrogen especially may leach below the root zone before plants can take it up in spring.
Volatilization
The potential for volatilization losses of nitrogen increases if fertilizer is applied to cold, wet soils. Under these conditions, gaseous ammonia may be lost into the atmosphere rather than taken up by plants.
Runoff
Dormant grass has a reduced ability to absorb applied fertilizer, increasing the risk of runoff during winter rains. Runoff can contaminate waterways and be a waste of product.
Lush Growth
While some green-up is desirable, excessive spring growth stimulated by winter nitrogen can deplete food reserves. Lush growth that occurs too early also risks damage from late frosts.
Increased Thatch
Applying too much nitrogen during times when grass grows slowly or not at all can lead to a buildup of excess organic matter known as thatch. Excessive thatch causes problems with root growth, moisture retention, and disease.
When to Fertilize
Timing is an important factor to consider when fertilizing dormant grass. Here are some guidelines on ideal application windows:
Cool-Season Grasses
Early fall is the best time to fertilize cool-season grasses before growth slows down. Late fall or early winter applications can also be beneficial. Avoid fertilizing once the ground has frozen.
Warm-Season Grasses
Apply fertilizer 6-8 weeks before warm-season grasses go dormant. Late fall applications on warm-season turf run a higher risk of leaching loss.
Northern Climates
Only one application during the fall pre-dormancy period is recommended in cold northern regions. Splitting the total nitrogen into fall and winter risks loss, especially on sandier soils.
Southern Climates
Split applications, with a light rate in late fall and another light rate during winter, work well in warmer southern climates where the dormant period is shorter.
What to Apply
Choosing an appropriate fertilizer source is key to getting benefits without causing excessive growth or leaching issues. Here are smart fertilizer options for dormant grass:
Slow-Release N
Polymer coated urea, sulphur coated urea, methylene urea sources, and natural organics release nitrogen slowly over an extended time period. This makes the nitrogen less prone to leaching.
Urea or Ammonium Sulfate
These fast-acting soluble nitrogen sources are cost-effective but risk heavier leaching losses. Only apply light rates and water in immediately after spreading.
Phosphorus and Potassium
Apply phosphorus unless soil tests show an excessive level. Potassium provides winter hardiness benefits to cool-season grasses.
Iron
Iron sources like ferrous sulfate give cool-season grasses a quick green-up boost and should be included in winter fertilizer mixes.
Application Methods
Proper application techniques can help mitigate some of the potential drawbacks of fertilizing dormant grass:
Granular Spreaders
Use drop spreaders for better accuracy and to avoid throwing fertilizer onto sidewalks and driveways where it will be wasted and can pollute waterways.
Water In
Irrigate immediately after applying soluble nitrogen sources to minimize volatilization and leaching.
Split Apps
Dividing the total nitrogen dose into two smaller apps spaced 4-6 weeks apart reduces risk compared to single heavy apps.
Soil Tests
Test soil nutrient levels first to avoid over-fertilization. Adjust amounts downward if phosphorus and potassium are already sufficient.
Reduce N Rate
Cut nitrogen rates by 1/3 to 1/2 compared to growing season apps to provide a gentle boost without surge growth.
Signs of Over-Fertilization
Watch for these cues that you may be applying too much fertilizer during grass dormancy:
Excessive Growth
Major growth flushes during winter cause lush, succulent grass with poor cold tolerance. Limit apps to 1/2 lb N per 1000 sq ft or less.
Green Tips
Green shoots emerging from dormant brown grass signal too much nitrogen is stimulating growth during cold periods.
Surge Growth
A spike of vigorous, excessive growth as temperatures rise indicates the turf was over-fertilized. Moderate spring green-up is ideal.
Floppiness
Overly lush, floppy growth that cannot support itself upright is a classic sign of fertilizer overdose. This weak growth is prone to disease.
Grass Types
The optimum approach to fertilizing dormant grass differs slightly depending on species. Here are specific tips for main grass types:
Cool-Season Grasses
Apply 1/2 to 1 lb N per 1000 sq ft in fall and another 1/4 to 1/2 lb N in late winter if needed based on spring green-up response. Include iron for color and PK for roots.
Warm-Season Grasses
Apply no more than 1 lb total N per 1000 sq ft in a single application 4-8 weeks before dormancy. Avoid winter apps on warm-season turf.
New Lawns
Fertilizing newly established lawns in fall and winter helps promote faster filling in and ground cover. Use 1 lb N per 1000 sq ft split over multiple apps.
High Maintenance Turf
Golf greens, sports fields, and other heavily used turf can benefit from spoon-feeding light biweekly rates up to 1 lb N per 1000 sq ft during winter.
| Grass Type | Total Nitrogen Rate | Ideal Timing |
|---|---|---|
| Cool-Season | 0.5 to 1 lb per 1000 sq ft | Late fall and early winter |
| Warm-Season | Up to 1 lb per 1000 sq ft | Late fall only |
| New Lawns | Up to 1 lb per 1000 sq ft | Split apps fall and winter |
| High Maintenance | Up to 1 lb per 1000 sq ft | Biweekly light doses |
The Bottom Line
Fertilizing grass while it is dormant is a somewhat controversial practice. There are benefits in terms of providing available nutrients just before spring green-up and enhancing root development over winter. However, there are also risks such as leaching, volatilization, runoff, and winter damage if growth occurs too early.
Ultimately, the advantages may outweigh the disadvantages in many cases, especially when proper fertilizer sources, rates, and application methods are used. A light dose of nitrogen in late fall followed by another lighter application in early winter, along with iron, phosphorus, and potassium provides the best insurance for vigorous spring transition.
Pay close attention to how your particular lawn responds. Adjust fertilizer types, amounts, and timing based on your specific grass species, soil conditions, and climate. With judicious use, applying fertilizer to dormant grass can be a helpful component of your overall winter lawn care program.