When it comes to fertilizing your lawn, timing is everything. Applying fertilizer at the right time of year can mean the difference between a lush, green lawn and one that is patchy and unhealthy. But when exactly should you fertilize? Here is a look at the best times to fertilize your lawn based on season and grass type.
Spring
For cool season grasses like bluegrass, ryegrass, and fescue, spring is the most important time to fertilize. Early spring is when these grasses break dormancy and start actively growing again after winter. Fertilizing in spring gives them a boost of nutrients to recover from winter damage and thrive. The best time is just as temperatures start warming up consistently, which is usually early to mid spring. This is often early April but can vary by region.
Apply a balanced fertilizer that contains nitrogen, phosphorus, and potassium at this time. The nitrogen encourages healthy green growth, phosphorus strengthens roots and stems, and potassium improves overall plant hardiness. Make sure to use a “weed and feed” type fertilizer as well to prevent weeds from invading in bare spots.
For warm season grasses like bermudagrass, zoysia, centipedegrass, and St. Augustinegrass, spring fertilization can wait until the grass is fully green and actively growing. This is usually late spring or early summer, around late May to early June for most warmer regions. Use a balanced fertilizer as well. Weed prevention is also important at this time.
Summer
Summer fertilization is crucial for warm season grasses. Early to mid summer (June to July) is when these grasses thrive. High temperatures, long days, and frequent rainfall create prime growing conditions. Fertilizing at this time fuels strong growth. Focus on nitrogen fertilizers now to keep the grass dark green and lush.
Cool season grasses are best fertilized in the spring and fall only. Summer fertilization is not necessary and can even damage fescue, bluegrass, and ryegrass. Excess nitrogen when the grass is stressed by heat and drought can scorch and thin out the lawn.
Fall
Fall is the second most important fertilization time for cool season grasses. Early fall (September to October) mimics spring conditions as temperatures moderate but adequate rainfall and warm soil temperatures remain. This fuels root growth and carbohydrate storage to prep the grass for winter dormancy. Use a balanced fertilizer to support overall plant health.
Warm season grasses can be fertilized again in early fall after summer growth slows down. This supplies nutrients for the last growth flush before winter dormancy. Discontinue fertilization by late fall to harden off the grass.
Winter
Avoid fertilizing any lawn during the winter months. Cool season grasses are completely dormant and fertilizer will simply leach away unused. Warm season grasses may remain semi-active in warm winter climates but growth is minimal and fertilizer is still ineffective.
The exception is using potassium or iron supplements on dormant lawns to improve hardiness, color, and root function. But nitrogen and phosphorus fertilizers should always be avoided in winter.
Best Fertilizer Types by Season
| Season | Cool Season Grasses | Warm Season Grasses |
|---|---|---|
| Spring | Balanced N-P-K fertilizer for growth and repair | Balanced N-P-K when grass is growing |
| Summer | None | Nitrogen for lush growth |
| Fall | Balanced N-P-K for winter prep | Balanced N-P-K for final flush |
| Winter | Iron, potassium only | Iron, potassium only |
How Much Fertilizer to Apply
Use the following guidelines for how much fertilizer to put down at each application:
- Cool season grasses: Apply 1 lb nitrogen per 1000 sq ft in spring and fall. For example, use a 20-5-10 fertilizer at a rate of 5 lbs per 1000 sq ft.
- Warm season grasses: Apply 1 to 1.5 lbs nitrogen per 1000 sq ft in early summer. For example, use a 30-0-10 at 3 to 4.5 lbs per 1000 sq ft.
- For foliar iron applications, apply according to product instructions, usually 2-4 oz per 1000 sq ft.
- When using combination products like weed-and-feed, calculate rates based on the nitrogen content.
- Heavier traffic areas may need slightly higher fertilization rates.
Always sweep or blow any fertilizer that lands on sidewalks or driveways back onto the lawn to prevent runoff. Irrigate after application to further reduce runoff potential.
Signs It’s Time to Fertilize
Look for the following signs that your lawn is due for fertilizer:
- Slow green-up and growth in spring
- Thin, spotty appearance
- Light green or yellowing color
- Decline in density and canopy thickness
- Poor recovery from foot traffic
- Inadequate growth and thickness
- Encroachment of weeds and moss
Cool season grasses may show deficiency signs in mid to late spring if fertilization was missed. Warm season grasses often show signs of hunger in mid summer after the early season nitrogen has run out.
Fertilizing New Lawns
Fertilization is critical when establishing a new lawn from seed or sod. Follow these tips for new lawns:
- Fertilize immediately after laying new sod to encourage fast rooting and establishment.
- Begin fertilizing new grass seed around 3-4 weeks after germination when the young grass reaches 2-3 inches tall.
- Use a starter fertilizer high in phosphorus to stimulate root system development.
- Fertilize every 4-6 weeks during the first season for stronger establishment.
- Reduce frequency to normal seasonal applications by the second year.
Best Fertilizer Sources
Look for lawn fertilizers that contain a combination of quick and slow release nitrogen:
- Quick release nitrogen from sources like ammonium sulfate, potassium nitrate, or urea for rapid green-up and growth. Avoid overusing these sources to prevent burn potential.
- Slow release nitrogen from sources like methylene urea, sulfur coated urea, resin coated urea, or biosolids for longer feeding duration.
Always check that the fertilizer contains potassium and phosphorus as well for balanced nutrition. Avoid weed-and-feed products when establishing new seedlings which can damage young grass.
Organic vs Synthetic Fertilizer
You can use either organic or synthetic fertilizer on your lawn:
- Organic fertilizers like compost, manure, corn gluten meal, and bone meal release nutrition more slowly over time. They improve soil biology and tilth.
- Synthetic fertilizers contain mineral salts and manufactured nutrients that are rapidly available to plants. They provide strong green-up response.
Consider combining both types of fertilizers in your seasonal lawn program for both quick green-up and sustained release effects.
Signs of Fertilizer Burn
Using too much fertilizer can damage lawn grass. Look for these signs of fertilizer burn:
- Brown leaf tips and streaks on grass blades
- Pale, yellowed grass
- Thinning and dieback of grass
- Footprints and wheel tracks that do not recover
- Distinct bands of brown grass from spreader overlap
To avoid fertilizer burn, always follow product label rates carefully. Never exceed 1 lb nitrogen per 1000 sq ft per application on established lawns. Water immediately after fertilizing to rinse fertilizer off grass leaves and incorporate into the soil.
Mowing After Fertilizing
Continue normal mowing after fertilizing, but never remove more than 1/3 of the grass blade height at one time. This is important to prevent scalping and additional grass damage. If possible, wait to mow for a couple days after fertilizing to allow the grass to grow and recover from any fertilizer burn effects.
Watering After Fertilizer Application
Proper watering after fertilizing helps move nutrients into the soil profile and prevents burn potential. Follow these tips:
- Water immediately after fertilizing, applying 1⁄4 to 1⁄2 inch of irrigation.
- Let the grass dry out slightly between watering to encourage deeper rooting.
- Continue regular irrigation based on your grass type’s needs to maintain growth.
- Adjust irrigation to rainfall so applying 1 inch of total water weekly.
Avoid excessive watering that results in leaching and runoff. Target deep, infrequent irrigation for stronger grass roots.
Fertilizing Problems to Avoid
Some common fertilizing mistakes lead to lawn damage. Be sure to avoid:
- Applying too much nitrogen leading to burn.
- Using quick release nitrogen sources only instead of a balanced fertilizer.
- Fertilizing during hot, dry weather creating burn potential.
- Failing to water in fertilizer which causes foliar burn.
- Applying fertilizer too early or late outside the ideal season.
- Not cleaning up spilled fertilizer from hardscapes which can wash off.
Careful timing and rate selection based on your grass type prevents many issues. Read all label instructions before applying.
Winterizing Fertilizer
Use a special winterizer fertilizer in late fall just before grass goes dormant. Look for formulas high in potassium and low in nitrogen. Benefits include:
- Hardening off the grass to improve winter survival.
- Increasing resistance to diseases and pests.
- Building root reserves for improved spring green-up.
- Reducing frost damage susceptibility.
- Strengthening turf density for fewer weeds.
Apply winterizer fertilizer 6-8 weeks before the ground typically freezes in your area. Water in well after application.
Conclusion
Proper timing and rates are the keys to effective lawn fertilization. Focus cool season grass applications in spring and fall, while fertilizing warm season grasses primarily in early to mid summer. Always use balanced fertilizer sources to prevent nutrient deficiencies. Follow label rates carefully, water thoroughly after applying, and time fertilizer based on your specific grass species’ needs for the healthiest, greenest lawn possible.
