When to Fertilize Flowering Shrubs for Bigger Blooms

Fertilizing flowering shrubs can help them grow stronger, produce more blooms, and recover from weather stress. But when it comes to fertilizer, more isn’t always better. The fertilizer you use in early spring may not be the right choice in late summer or fall. In fact, feeding shrubs at the wrong time can encourage tender new growth just before cold weather arrives, reduce flowering, or even damage the roots.

Let’s walk through what fertilizer to use during each season and when your flowering shrubs may not need fertilizer at all.

UGA Extension recommends fertilizing shrubs in early spring and using a soil test to determine what nutrients are actually needed.

Start With the Soil

Before buying fertilizer, take a good look at the shrub and the soil around it.

A shrub may not need fertilizer if it:

• Produces healthy green leaves
• Grows a reasonable amount each year
• Blooms normally
• Shows no obvious nutrient deficiencies

Poor growth isn’t always caused by a lack of fertilizer. Compacted soil, improper watering, root damage, too much shade, poor drainage, and incorrect pruning can all affect a shrub’s health.

A soil test is the best way to know what your soil actually needs. It can tell you the soil’s pH and whether nutrients such as phosphorus or potassium are low. Without a soil test, you’re mostly guessing.

Understanding Fertilizer Numbers

You’ve probably seen three numbers printed on fertilizer bags, such as 10-10-10 or 12-4-8. These numbers represent:

• Nitrogen: Encourages green leaves and new growth
• Phosphorus: Supports roots and flowering
• Potassium: Helps with overall plant strength, stress tolerance, and disease resistance

A balanced fertilizer contains similar amounts of all three nutrients. However, flowering shrubs don’t always need equal amounts of everything.

Adding extra phosphorus won’t automatically create more flowers if the soil already contains enough. Too much nitrogen can also give you a beautiful green shrub with very few blooms.

Early Spring: Wake Shrubs Up Slowly

Early spring is one of the best times to fertilize many flowering shrubs. Apply fertilizer when the shrub begins showing signs of new growth but before it enters its busiest growing and blooming period.

A slow-release shrub and tree fertilizer is usually a good choice. Look for a balanced or slightly nitrogen-forward formula designed for woody plants.

Good early-spring choices may include:

• Slow-release shrub fertilizer
• Balanced granular fertilizer
• Compost worked gently into the soil surface
• Well-aged manure used in moderation

Follow the package directions and spread the fertilizer around the shrub’s root zone. Don’t pile it against the trunk or stems.

The feeder roots usually extend beyond the center of the plant, so spread the fertilizer beneath the branches and around the outer edge of the shrub.

Shrubs That May Benefit From Spring Feeding

Spring fertilizer may help:

• Hydrangeas
• Roses of Sharon
• Weigelas
• Butterfly bushes
• Crape myrtles
• Forsythias
• Spireas
• Viburnums
• Panicle hydrangeas
• Smooth hydrangeas

Remember that some shrubs bloom on old wood. Fertilizer can support healthy growth, but it cannot replace flower buds that were removed by pruning or damaged by a late freeze.

Late Spring: Support Growth Without Overfeeding

By late spring, many shrubs are actively growing or beginning to flower. If you already applied a slow-release fertilizer in early spring, you probably don’t need to fertilize again.

Shrubs growing in containers or poor soil may need another light feeding, but avoid repeatedly adding strong fertilizer just because the plant is growing slowly.

For a light late-spring feeding, consider:

• A mild slow-release fertilizer
• Compost around the root zone
• A diluted liquid fertilizer for container-grown shrubs
• A fertilizer made for acid-loving plants when appropriate

Azaleas, rhododendrons, gardenias, and some hydrangeas may benefit from fertilizer formulated for acid-loving plants. However, only use these products when the soil pH and the plant’s needs call for them.

Summer: Be Careful With Fertilizer

Summer is when gardeners often make fertilizer mistakes.

When the weather is hot and dry, shrubs are already under stress. Applying a strong fertilizer to dry soil can burn the roots and place even more stress on the plant.

During summer, watering and maintaining mulch are usually more important than feeding.

Avoid fertilizing shrubs when:

• The soil is extremely dry
• The shrub is wilted from heat
• Temperatures are unusually high
• The shrub was recently transplanted
• The plant is showing signs of root rot or poor drainage

If a shrub clearly needs nutrients during early summer, use a light application of slow-release fertilizer and water it in well. Container shrubs may need occasional diluted liquid fertilizer because nutrients wash out of pots more quickly.

Stop using high-nitrogen fertilizer as summer moves along. Nitrogen encourages tender new growth, and that new growth may not have enough time to harden before colder weather arrives.

Late Summer: Put Down the High-Nitrogen Fertilizer

By late summer, most established flowering shrubs should no longer receive a heavy feeding.

This is especially important in areas where frost and freezing temperatures arrive in fall or winter. New growth produced after a late fertilizer application may be damaged by cold weather.

During late summer, focus on:

• Consistent watering
• Maintaining two to three inches of mulch
• Removing badly damaged branches
• Watching for pests and diseases
• Allowing new growth to mature naturally

A shrub that looks tired in August may simply be reacting to heat. Fertilizer won’t fix heat stress, underwatering, or scorched leaves.

Fall: Feed the Soil, Not the Leaves

Fall usually isn’t the time to push leafy growth. Instead, concentrate on improving the soil and protecting the roots.

A light layer of compost can be applied around established shrubs in fall. Compost improves soil structure and slowly releases nutrients without forcing a sudden flush of growth.

Good fall choices include:

• Finished compost
• Shredded leaves
• Organic mulch
• Soil amendments recommended by a soil test

Avoid applying a heavy dose of quick-release nitrogen fertilizer in fall.

Some fertilizer products are marketed as fall fertilizers because they contain less nitrogen and more potassium. These may be useful when a soil test shows a need, but they shouldn’t be applied automatically to every shrub in the yard.

Winter: Let the Shrubs Rest

Most flowering shrubs don’t need fertilizer during winter.

The plants may be dormant, but their roots still need protection from extreme temperature changes. Maintain a proper mulch layer, but keep the mulch a few inches away from trunks and stems.

Winter is a good time to:

• Schedule a soil test
• Review which shrubs bloomed well
• Check fertilizer expiration dates
• Plan next year’s feeding schedule
• Add compost after the ground cools, when appropriate

Fertilizing dormant shrubs with a quick-release product usually wastes fertilizer and may allow nutrients to wash away before the plant can use them.

What About Newly Planted Shrubs?

Newly planted shrubs usually don’t need strong fertilizer right away.

Their first job is to establish a healthy root system. A heavy fertilizer application can burn young roots or encourage top growth before the roots are ready to support it.

When planting a new shrub:

1. Dig a wide planting hole.
2. Plant at the correct depth.
3. Backfill mainly with the native soil.
4. Water deeply.
5. Apply mulch around the root zone.
6. Wait until the shrub begins establishing before applying fertilizer.

You can add a thin layer of compost around the planting area, but avoid placing concentrated fertilizer directly in the planting hole unless the product specifically says it is safe for that use.

Special Fertilizer Considerations for Hydrangeas

Hydrangeas are often overfertilized because gardeners believe more fertilizer will create more flowers.

Too much nitrogen can produce a large, leafy hydrangea with disappointing blooms. One spring application of slow-release fertilizer is often enough for an established plant.

If a hydrangea isn’t blooming, check these issues before adding more fertilizer:

• Was it pruned at the wrong time?
• Did cold weather damage the flower buds?
• Is it receiving enough sunlight?
• Is it a young plant that is still becoming established?
• Is it getting too much nitrogen from lawn fertilizer?
• Is it receiving enough water?

Bigleaf hydrangea flower color is also affected by soil chemistry. Aluminum availability and soil pH influence whether certain varieties bloom blue or pink. Regular fertilizer alone won’t reliably change flower color.

Keep Lawn Fertilizer Away From Shrubs

Flowering shrubs planted near lawns can accidentally receive too much nitrogen from lawn fertilizer.

This can cause:

• Excessive leafy growth
• Fewer flowers
• Weak stems
• Increased pest problems
• Tender growth late in the season

Be careful when using spreaders near flower beds. Sweep fertilizer granules off sidewalks, driveways, leaves, and plant crowns after applying.

Signs You May Be Using Too Much Fertilizer

Overfertilized shrubs may show:

• Brown or burned leaf edges
• Wilting even though the soil is moist
• White fertilizer crust on the soil
• Long, weak stems
• Lots of leaves but few flowers
• Sudden leaf drop
• Damaged or blackened roots

If you believe too much fertilizer was applied, stop feeding the plant and water the soil deeply to help move excess salts away from the root zone, as long as the area drains properly.

A Simple Seasonal Fertilizer Schedule

Here’s an easy schedule for most established flowering shrubs:

Early spring: Apply slow-release fertilizer if the shrub needs it.

Late spring: Add compost or provide a light feeding only when necessary.

Early summer: Fertilize container shrubs lightly, but avoid feeding heat-stressed plants.

Late summer: Stop high-nitrogen fertilizer and allow new growth to harden.

Fall: Add compost, leaves, or mulch instead of pushing new growth.

Winter: Don’t fertilize. Test the soil and plan for spring.

The Bottom Line

Flowering shrubs don’t need to be fed every few weeks to look good.

For most established shrubs, one properly timed spring application of slow-release fertilizer may be all they need. Compost, proper watering, mulch, sunlight, and correct pruning are just as important—sometimes even more important—than what comes out of a fertilizer bag.

Pay attention to the plant, follow the fertilizer label, and don’t assume that more fertilizer means more flowers. In the garden, a little patience and the right timing usually work better than trying to push a plant too hard.

Need More Hydrangea Help?

Still have questions about your hydrangea? Visit our Hydrangea Help page for practical guides on pruning, watering, fertilizing, blooming problems, brown leaves, drooping flowers, and more.

Whether you’re trying to identify your hydrangea or figure out why it isn’t blooming, we’ll help you find the right information without making things more complicated than they need to be.

Visit the Hydrangea Help page →