Extended-release fertilizers—also called slow-release or controlled-release fertilizers—have changed the way we feed plants. By steadily providing nutrients over time, they encourage stronger growth, cut down on environmental waste, and save time and money. This guide explains what extended-release fertilizers are, how to use them properly, and the best practices to get the most out of them.
What Is Extended-Release Fertilizer?
Extended-release fertilizer is designed to release nutrients gradually over a period of weeks or months. Unlike quick-release options that deliver nutrients all at once, these fertilizers feed plants slowly and consistently. This aligns better with how plants naturally absorb nutrients.
How It Works
There are two main ways these fertilizers release nutrients:
- Coated Granules: These have a layer (often sulfur or a synthetic polymer) that water penetrates. Once inside, water dissolves the nutrients, which then seep out slowly.
- Chemical Composition: Some use compounds that break down slowly through microbial activity, like urea-formaldehyde or IBDU (isobutylidene diurea).
The release rate depends on factors like soil temperature, moisture levels, and microbial activity. Warmer, wetter conditions usually speed things up, while cooler, dry conditions slow the process.
Benefits of Using Extended-Release Fertilizer
1. Steady Nutrient Supply
Because they release nutrients over time, these fertilizers provide a more even supply to plants. That leads to balanced growth, fewer nutrient spikes, and less risk of deficiency or overfeeding.
2. Better for the Environment
Slow-release products are less likely to cause runoff or leaching into groundwater. This means less pollution, especially in areas near rivers, lakes, or oceans.
3. Saves Time and Effort
Fewer applications are needed. Many extended-release products only need to be applied once per season, saving you time and reducing the labor involved in lawn or garden maintenance.
4. Low Risk of Burn
Since the nutrients are released gradually, there’s a much lower risk of damaging your plants by overfeeding them.
Types of Extended-Release Fertilizers
Understanding the different types helps you choose the right one for your needs.
Sulfur-Coated Urea (SCU)
This type uses a layer of sulfur around each urea granule. As the sulfur slowly breaks down, the urea inside dissolves and becomes available to plants.
Polymer-Coated Fertilizers
These use a synthetic coating that controls how quickly water gets in and nutrients get out. They can last anywhere from six weeks to six months, depending on the coating.
Urea-Formaldehyde and IBDU
These are slow-release due to their chemical makeup, which requires microbial activity to break down. They’re especially useful in cooler climates, where coated fertilizers might take too long to activate.
How to Use Extended-Release Fertilizer
Step 1: Test Your Soil
Start with a soil test to check nutrient levels and pH. This helps you avoid guessing and ensures your plants get what they actually need.
Step 2: Choose the Right Fertilizer
Match the fertilizer to your plant type and growth stage. For example:
- Lawns may need high-nitrogen formulas.
- Flowering plants often benefit from a balanced mix (like 10-10-10).
- Vegetables may require more phosphorus and potassium.
Also, consider how long the product lasts. Some are made to release nutrients over 6 weeks, others over 6 months.
Step 3: Pick the Right Application Method
There are several ways to apply extended-release fertilizers:
- Broadcasting: Spread it evenly over the soil surface. Ideal for lawns or large garden beds.
- Banding: Place it in a line near plant rows. Common in vegetable gardens.
- Side-Dressing: Apply around growing plants during the season to give an extra boost.
- Top-Dressing: Sprinkle around established plants, letting rain or irrigation move nutrients into the root zone.
Step 4: Apply at the Right Time
Apply during the plant’s active growing season—typically spring or early summer for most plants. Avoid applying right before heavy rain to reduce nutrient runoff.
Tips for Best Results
Read the Label
This can’t be overstated. Follow the manufacturer’s instructions carefully for how much to use and how to apply it. Overdoing it doesn’t speed up growth—it can actually harm plants.
Water After Application
Most extended-release fertilizers need water to activate. After applying, water the area thoroughly unless rain is expected soon.
Watch the Weather
Avoid applying fertilizer during extreme heat or right before a storm. Both conditions can disrupt nutrient release and effectiveness.
Combine with Compost
Adding compost improves soil texture and boosts microbial activity. This helps your fertilizer work more efficiently and provides even more long-term benefits.
Mistakes to Avoid
Using Too Much
This is one of the most common mistakes. More isn’t better. Overapplication can stress your plants and waste money.
Skipping the Soil Test
Guessing what your soil needs is like throwing darts in the dark. Soil tests are cheap, easy, and extremely useful.
Uneven Application
If fertilizer is applied unevenly, you’ll get patchy results. Use a broadcast spreader or measure carefully if you’re applying by hand.
Relying on Fertilizer Alone
Healthy soil needs more than nutrients. Organic matter, good drainage, and proper pH all play a role. Don’t overlook these basics.
When to Use Extended-Release Fertilizer
Lawns
Early spring is ideal. Use a nitrogen-rich slow-release product to encourage steady green-up without sudden spurts.
Flower Beds
Apply in early spring, just as new growth starts. A balanced formula will support blooms throughout the season.
Vegetables
For long-season crops like tomatoes or peppers, use extended-release fertilizer at planting time. Side-dress mid-season if needed.
Trees and Shrubs
Apply once in early spring. These plants benefit from deep, steady feeding that encourages root growth and resilience.
Frequently Asked Questions
How Long Does Extended-Release Fertilizer Last?
It depends on the product. Some last 6 to 8 weeks, while others can feed plants for up to 6 months. Check the label for specifics.
Can I Use It with Other Fertilizers?
Yes—but be cautious. If you use a quick-release fertilizer too soon after applying a slow-release one, you might end up overfeeding. If in doubt, wait at least a month between applications.
Does It Work in Cold Weather?
Chemical-based slow-release fertilizers like IBDU still release nutrients in cool soil. However, coated types often need warmth and moisture, so they may be less effective in colder months.
Final Thoughts
Extended-release fertilizers make gardening and landscaping more efficient, sustainable, and lower maintenance. They cut down on how often you need to feed your plants and protect the environment by reducing runoff and waste.
By understanding how these fertilizers work, testing your soil, choosing the right formula, and applying it correctly, you’ll get better growth and stronger, healthier plants with less effort.
Take the time to apply it right—and you’ll see the long-term payoff in healthier lawns, fuller blooms, and better harvests.
