Best Nasturtium Fertilizers

Nasturtiums produce more flowers when grown in lean soil without extra feeding, which makes finding the best nasturtium fertilizers a bit counterintuitive. Most gardeners actually harm their nasturtiums by over-fertilizing, leading to lush leaves but few blooms.

Here’s the truth: these plants thrive on neglect. But sometimes, especially in poor soil or containers, a light hand with the right feed can help. This guide covers exactly what to use and what to avoid.

Why Nasturtiums Dislike Rich Soil

Nasturtiums are native to poor, rocky soils in South America. They evolved to bloom best when nutrients are scarce. When you add too much nitrogen, the plant puts all its energy into leaves instead of flowers.

Think of it like this: a stressed nasturtium flowers more because it’s trying to reproduce before conditions get worse. A happy, well-fed plant just grows bigger leaves.

So the goal isn’t to feed them heavily. It’s to provide just enough support without triggering leaf growth.

The best nasturtium fertilizers are low in nitrogen and higher in phosphorus and potassium. Look for a balanced fertilizer like 5-10-10 or a bloom booster like 0-10-10. Avoid anything with high first numbers (like 20-20-20).

Here are the top options:

Bone meal: High in phosphorus, promotes flowers. Sprinkle lightly around the base.
Rock phosphate: Slow-release phosphorus source. Good for long-term blooms.
Compost tea: Diluted and weak. Use only if soil is extremely poor.
Liquid seaweed: Contains trace minerals. Use at half strength.
Banana peel water: Soak peels in water for 24 hours. Provides potassium.

Never use synthetic high-nitrogen fertilizers like lawn food or all-purpose plant food. They will ruin your nasturtiums.

When To Fertilize Nasturtiums

Timing matters more than the product. Here’s a simple schedule:

At planting: Mix a small amount of bone meal into the soil. No more than a teaspoon per plant.
When buds appear: Apply a weak liquid fertilizer (half strength) once.
Mid-season: Only if leaves look pale or growth is stunted. Use compost tea or seaweed.
Stop by late summer: Let the plant finish naturally.

If your nasturtiums are already flowering well, don’t fertilize at all. You’ll just upset the balance.

Signs You’re Over-Fertilizing

Watch for these red flags:

Huge, dark green leaves with no flowers
Leaves that are soft and easily damaged
Yellowing leaf edges (salt burn)
Stunted growth or wilting despite moist soil
Few or no buds forming

If you see these, stop fertilizing immediately. Flush the soil with water to remove excess nutrients. Your plants will recover in a few weeks.

Soil Preparation Matters More

Before you think about fertilizers, focus on soil. Nasturtiums prefer well-draining, sandy or loamy soil with low organic matter. Heavy clay or rich compost causes problems.

Here’s how to prepare the perfect bed:

Choose a spot with full sun (6+ hours daily).
Mix in sand or perlite if soil is heavy.
Avoid adding compost or manure. It’s too rich.
Test drainage: water should soak in within 10 minutes.
Add a thin layer of gravel if drainage is poor.

Good soil means you rarely need fertilizer. Bad soil means you’ll fight problems all season.

Container Growing Considerations

Potted nasturtiums need slightly more care because nutrients wash out faster. But still go easy.

Use a potting mix labeled “for cacti and succulents” or mix regular potting soil with 30% sand. Add a teaspoon of bone meal at planting. Then water with diluted seaweed every 3-4 weeks during blooming.

Never use slow-release fertilizer pellets. They release too much nitrogen at once.

Organic Vs Synthetic Fertilizers

Organic options are safer because they release nutrients slowly. Synthetic fertilizers can burn roots and cause salt buildup.

Best organic choices:

Bone meal (phosphorus)
Rock phosphate (phosphorus)
Greensand (potassium and trace minerals)
Compost (use sparingly, only if soil is very poor)
Worm castings (thin layer only)

Synthetic options to avoid:

Miracle-Gro (too much nitrogen)
Any fertilizer with N over 10
Water-soluble all-purpose feeds
Lawn fertilizers

If you must use synthetic, choose a bloom booster with numbers like 0-10-10 and use at quarter strength.

How To Apply Fertilizer Correctly

Less is more. Follow these steps:

Water the soil first (never apply to dry soil).
Mix liquid fertilizer at half the recommended rate.
Pour around the base, not on leaves.
Water again lightly to distribute.
Wait 2 weeks before reapplying.

For granular fertilizers, sprinkle a pinch (not a handful) around each plant. Scratch it into the top inch of soil. Water well.

Common Mistakes With Nasturtium Feeding

Even experienced gardeners make these errors:

Fertilizing too often: Once a month is plenty, if at all.
Using high-nitrogen feeds: You get leaves, no flowers.
Applying to wet leaves: Causes burn and fungal issues.
Adding too much compost: Makes soil too rich.
Fertilizing in cool weather: Plants can’t use it and roots may burn.

Avoid these and your nasturtiums will reward you with continuous blooms from summer to frost.

What About Companion Planting Benefits

Nasturtiums are often used as trap crops for aphids. They also repel some pests. But companion planting doesn’t replace fertilizer needs.

If you grow nasturtiums near vegetables, be careful. The vegetables may need more fertilizer than the nasturtiums. Keep them separate or use a barrier.

Some gardeners say nasturtiums improve soil for neighbors by attracting beneficial insects. This is true, but it doesn’t feed the nasturtiums themselves.

Seasonal Fertilizer Guide

Here’s a month-by-month breakdown for temperate climates:

Spring (April-May): Prepare soil with bone meal at planting. No other feeding needed for 4-6 weeks.

Early Summer (June): If plants look pale, apply one weak dose of seaweed fertilizer. Otherwise skip.

Mid-Summer (July): Peak blooming. Don’t fertilize unless you see clear deficiency signs like yellow lower leaves.

Late Summer (August): Stop all fertilizing. Let plants wind down naturally.

Fall (September-October): Collect seeds for next year. Remove spent plants. Don’t add fertilizer to soil for winter.

Adjust based on your local climate. In hot areas, growth slows in summer, so fertilize less.

Testing Your Soil First

Before you buy any fertilizer, test your soil. Cheap home kits work fine. Check for:

pH level (ideal is 6.0-7.0)
Nitrogen content (should be low)
Phosphorus (moderate is fine)
Potassium (low to moderate)

If your soil already has adequate phosphorus and potassium, don’t add more. Excess phosphorus can harm beneficial soil fungi.

Nasturtiums actually bloom better in slightly deficient soil. So if tests show “adequate” or “high,” skip fertilizing entirely.

DIY Fertilizer Recipes

You can make your own low-nitrogen feeds at home:

Banana Peel Tea: Soak 3 banana peels in 1 liter of water for 48 hours. Dilute with equal parts water. Use once.

Eggshell Water: Boil 6 eggshells in 1 liter of water. Cool and strain. Provides calcium but very low nitrogen.

Compost Leachate: Collect liquid that drains from compost pile. Dilute 1:10 with water. Use sparingly.

Weed Tea: Soak weeds (no seeds) in water for 2 weeks. Dilute 1:5. Use only if weeds are low-nitrogen types like dandelion.

These homemade options are weak but safe. They won’t burn roots or cause leaf overload.

When Not To Fertilize At All

There are clear situations where fertilizing does more harm than good:

Soil is already rich (dark, crumbly, full of worms)
Plants are flowering well already
Leaves are dark green and large
Weather is very hot (above 90°F/32°C)
Plants are stressed from pests or disease
You’re growing in ground with good native soil

In these cases, the best fertilizer is no fertilizer. Just water when dry and enjoy the blooms.

Frequently Asked Questions

Can I use coffee grounds on nasturtiums?

No. Coffee grounds are acidic and high in nitrogen. They can harm nasturtiums and reduce flowering. Use them on acid-loving plants like blueberries instead.

What is the best natural fertilizer for nasturtiums?

Bone meal is the best natural option. It provides phosphorus for blooms without adding nitrogen. Apply a teaspoon per plant at planting time.

How often should I fertilize nasturtiums in pots?

Once every 3-4 weeks with a weak liquid fertilizer (half strength). Use a bloom booster like 0-10-10. Stop by mid-summer.

Do nasturtiums need fertilizer if planted in compost?

No. Compost is already rich enough. Adding fertilizer will cause leaf growth at the expense of flowers. Only fertilize if soil is very poor.

Can I use Epsom salt on nasturtiums?

Not recommended. Epsom salt provides magnesium and sulfur, which can stimulate leaf growth. Nasturtiums don’t need extra magnesium in most soils.

Final Tips For Maximum Blooms

Remember the golden rule: starve your nasturtiums for flowers, feed them for leaves. If you want a show of color, keep fertilizer to a minimum.

Focus on these priorities instead:

Full sun exposure
Well-draining, lean soil
Regular deadheading of spent blooms
Moderate watering (let soil dry between waterings)
Good air circulation to prevent mildew

When you do use fertilizer, choose one specifically designed for blooming plants. Check the N-P-K ratio and make sure the first number is low. A 5-10-10 or 0-10-10 formula works best.

Apply sparingly and only when needed. Your nasturtiums will thank you with a cascade of vibrant flowers from early summer until the first frost.

One last thing: if your nasturtiums are growing in average garden soil, you probably don’t need any fertilizer at all. Save your money and your effort. Just plant them in a sunny spot, water occasionally, and watch them thrive on neglect.

That’s the real secret to the best nasturtium fertilizers: using them so rarely that they barely matter. Your plants will bloom better for it.