Understanding N-P-K, Slow-Release Nitrogen & Micronutrients

A Boise Gardener’s Guide to Healthier Plants All Season Long

If you’ve ever stood in the fertilizer aisle wondering what those three numbers mean—10-10-10, 16-4-8, 24-0-6 - you’re not alone.

Those numbers represent Nitrogen (N), Phosphorus (P), and Potassium (K) and is the foundation of plant nutrition. But here’s what many gardeners in Boise don’t realize:

It’s not just the numbers that matter, it’s the form of those nutrients, especially during our hot summer months.

Nitrogen (N): The Growth Engine

Nitrogen drives leafy growth and gives plants their rich green color.

Common Forms of Nitrogen

• Nitrate (NO₃⁻): Fast-acting, quick green-up

• Ammonium (NH₄⁺): Longer-lasting, more stable

• Urea: Converts over time, widely used

Why Slow-Release Nitrogen is Critical in Boise Summers

Hot, dry summers in Boise create unique challenges:

• Fast-release fertilizers can burn plants

• Nutrients can leach away with irrigation

• Plants get stressed and can’t keep up with rapid growth

Sulfur-Coated Urea (SCU)

What it does:

• Releases nitrogen slowly as the sulfur coating breaks down

Why it works here:

• Prevents fertilizer burn

• Feeds plants steadily during heat

• Adds beneficial sulfur to the soil

“Sulfur-coated urea provides steady nitrogen release during hot summer months.”

Polymer-Coated Nitrogen (PCU)

Sometimes referred to as encapsulated nitrogen, this is a premium option.

What it does:

• Releases nutrients based on temperature and moisture

Why it’s ideal:

• Feeds plants when they need it most

• Prevents excessive growth during heat waves

• Long-lasting and efficient

  

  “Sulfur-coated urea provides steady nitrogen release during hot summer months.”

  Phosphorus (P): Root & Bloom Power

Phosphorus supports:

• Root development

• Flowering

• Fruit production

 “Phosphorus fuels blooms and strong root systems.”

Potassium (K): Strength & Protection

Potassium improves:

• Drought tolerance

• Disease resistance

• Overall plant durability

“Potassium helps plants withstand heat and stress.”

Iron & Sulfur: The Missing Link in Many Boise Landscapes

Here’s where many local gardeners run into trouble.

Iron (Fe): The Key to Deep Green Color

Iron is essential for chlorophyll production, but in Boise soils, it’s often locked up due to our high pH.

Signs of iron deficiency:

• Yellow leaves with dark green veins

• Common in lawns, maples, and ornamentals

Sulfur (S): The Nutrient Unlocker

Sulfur plays a critical supporting role:

• Helps form plant proteins

• Improves nutrient uptake

• Slightly lowers soil pH

🔗 Why Iron and Sulfur Work Together

This is especially important for The Treasure Valley:

• High pH soils block iron uptake

• Sulfur helps make iron available again

Simply adding iron often isn’t enough 

Adding sulfur helps plants actually use that iron

Putting It All Together

For gardeners in Boise:

• Use slow-release nitrogen in summer - Ferti-lome “Classic” Lawn Food

• Address yellowing with iron + sulfur together - Hi-Yield “IronPlus”

• Avoid overfeeding during extreme heat

What to Look for at The Home & Garden Store

When helping customers (or stocking your own garden), look for:

• Fertilizers with coated or slow-release nitrogen - Ferti-lome “Classic Lawn Food”

• Products containing iron and sulfur combinations - Hi-Yield "IronPlus"

• Seasonally appropriate blends (spring vs. summer vs. fall)

Pro Tip: Ferti-lome “GreenMaker”, a fertilizer specifically formulated for our high pH soils, it certainly can make a big difference in our area.

Final Thoughts

Great gardening in Boise isn’t just about watering and sunlight, it’s about understanding how nutrients behave in our unique climate and soils.

By choosing the right forms of nitrogen and supporting your plants with iron and sulfur, you’ll see:

• Greener lawns

• Healthier plants

• Better blooms and harvests

Recommended Products for Boise Lawns & Gardens

At The Home & Garden Store, we’re big believers in using the right product for the right conditions, especially here in Boise where alkaline soils and hot summers create unique challenges.

Here are a few of our top-performing fertilizers and soil conditioners:

Lawn Color + Iron + Sulfur Solution

Ferti-lome Green Maker Lawn Food

Ferti-lome GreenMaker

• Designed specifically for alkaline soils

• Contains iron for deep green color

• Includes sulfur to help unlock nutrients

• Excellent for correcting chlorosis (yellowing)

This is one of the best “Boise-specific” fertilizers you can use

Ferti-lome Classic Lawn Food (16-0-8)

• Contains polymer-coated AND sulfur-coated nitrogen

• Provides slow, steady feeding for up to 2 months

• Reduces surge growth and mowing

Perfect for summer feeding when fast-release nitrogen can stress lawns

Soil Health & Nutrient Efficiency Boosters

Ferti-lome Liquid Humic Acid

Ferti-lome Chelated Liquid Iron

Ferti-lome Humates (Humic Acid)

• Improves soil structure and microbial activity

• Helps plants absorb nutrients more efficiently

• Increases water retention—huge benefit in our dry climate

If there’s one “secret weapon” for Boise soils—this is it

Ferti-lome Chelated Iron

• Quickly corrects yellowing (iron chlorosis)

• Works especially well in high pH soils

• Can be applied as a foliar spray or soil drench

Best used in combination with sulfur-based fertilizers

Bonus Recommendations for Complete Plant Health

• Ferti-lome Gardener’s Special Plant Food

  → Great all-purpose option with both fast and slow nitrogen

• Ferti-lome Blooming & Rooting Plant Food (9-58-8)

  → Ideal for flowers, vegetables, and boosting blooms

• Ferti-lome Tree & Shrub Food (19-8-10)

  → Perfect for deeper root feeding of landscape plants

How to Use These Products Together (Simple Program)

For our gardening customers, you can simplify everything like this:

Spring:

• GreenMaker (iron + sulfur boost)

• Add humates to build soil

Early Summer:

• Classic Lawn Food (slow-release nitrogen)

Mid-Summer (heat stress period):

• Light feeding only (slow-release if needed)

• Apply chelated iron if yellowing appears

Fall:

• Reapply humates

• Balanced fertilizer for root development

Final Takeaway for Our Customers

If we had to simplify it down to just a few key recommendations:

• GreenMaker → fixes color and soil issues

• Classic → feeds safely through summer

• Humates → improves everything below the surface

  
  

These combinations are incredibly effective for the conditions we deal with in Boise.