When To Fertilize Geraniums

Knowing when to fertilize geraniums is the single most important factor for getting those vibrant, non-stop blooms we all love. If you get the timing wrong, you might end up with lots of green leaves but few flowers, which is a common frustration. This guide will walk you through the simple schedule and methods that ensure your geraniums are fed perfectly for maximum color.

Geraniums, whether they’re the classic zonal types in pots or hardy geraniums in borders, are actually quite heavy feeders during their growing season. They use up a lot of energy to produce those generous flower clusters. Feeding them correctly supports strong roots, healthy foliage, and most importantly, triggers and sustains that spectacular bloom show from spring right through until fall.

Let’s break down the fertilizing calendar into three key phases: starting up in spring, maintaining through summer, and winding down in fall.

The Spring Kick-Start

Begin fertilizing in early spring, just as you see new growth emerging. This is typically when daytime temperatures are consistently above 55°F (13°C) and the danger of a hard frost has passed. If you’re planting new geraniums or repotting old ones, mix a slow-release granular fertilizer into the soil at this time. This provides a steady base of nutrients.

For in-ground geraniums: Start feeding 4-6 weeks after planting.
For potted geraniums: Begin 2-3 weeks after you see new growth or after bringing indoor plants outside.

At this stage, use a balanced fertilizer to encourage all-around health. A formula like 10-10-10 or 20-20-20 works well to get them going strong.

The Summer Feast for Blooms

Once your geraniums are actively growing and forming buds, it’s time to switch your strategy. For the most vibrant blooms, geraniums benefit from more phosphorus—the middle number in the N-P-K ratio on fertilizer packages.

Switch to a bloom-booster formula, such as 5-10-5 or 10-20-10.
Fertilize every 2 to 4 weeks throughout the summer months.
If you use a liquid fertilizer, it’s easy to apply it while your watering. Just follow the dilution instructions on the label.

Consistency is key here. Regular feeding supports continuous flowering, as geraniums will quickly use up the available nutrients in a container or garden bed.

The Fall Wind-Down

As autumn approaches and temperatures begin to cool, you need to stop fertilizing. This is crucial. Feeding too late in the season encourages tender new growth that will be damaged by frost.

Stop all fertilization about 6 to 8 weeks before your area’s first expected frost date.
This allows the plant to naturally harden off and prepare for dormancy or for being brought indoors.

If you are overwintering your geraniums indoors, do not fertilize them during the winter. They are resting and too much food can cause weak, leggy growth.

Special Timing for Different Geranium Types

Not all geraniums have exactly the same needs. Here’s a quick guide:

Zonal & Ivy Geraniums (Pelargoniums): Follow the standard spring-start/summer-feed/fall-stop schedule strictly. They are the heaviest feeders.
Hardy Geraniums (Cranesbills): These perennial types need less. A single application of a balanced fertilizer in early spring and maybe another light feeding after their first major bloom is often sufficient.
Regal Geraniums (Martha Washington): They prefer cooler weather and bloom heavily in spring. Fertilize them well in spring and early summer, but they often take a break from blooming in peak heat.

How to Fertilize Geraniums Correctly

Knowing when to feed is half the battle; applying it correctly is the other half. Here’s a simple step-by-step method.

Step 1: Water First

Always water your geraniums thoroughly with plain water before applying liquid fertilizer. Applying fertilizer to dry soil can shock the roots and cause root burn, which can seriously damage the plant.

Step 2: Mix and Apply

If using a liquid fertilizer, mix it according to the package directions. It’s better to err on the side of a slightly weaker solution than a stronger one. Apply the fertilizer directly to the soil around the base of the plant, avoiding the leaves and stems.

Step 3: Regular Watering Routine

After fertilizing, continue with your normal watering routine, allowing the soil to dry out slightly between waterings. Well-draining soil is essential to prevent root rot, especialy in pots.

Choosing the Best Fertilizer

Walking down the garden center aisle can be confusing. Here’s what to look for:

Water-Soluble Fertilizers: These are fast-acting and great for container geraniums. They require more frequent application (every 2-3 weeks).
Slow-Release Granules: These are mixed into the soil and feed the plant gradually over 3 to 4 months. They provide a great baseline, reducing how often you need to remember to feed.
Organic Options: Fish emulsion, seaweed extract, or compost tea are excellent choices. They feed the plant and improve soil health. They may need to be applied more frequently than synthetic options.

The key is to choose a fertilizer with a higher phosphorus (P) number during the blooming period for those vibrant flower heads.

Signs You’re Fertilizing Wrong

Your geraniums will tell you if the feeding schedule is off. Keep an eye out for these signals:

Lush Leaves, Few Flowers: This usually means too much nitrogen (the first number). Switch to a bloom-booster formula.
Yellowing Lower Leaves: This can be a sign of hunger, especially if the plant is otherwise healthy. It might need more frequent feeding or a slightly stronger solution.
Brown Leaf Edges or Wilting: This often indicates fertilizer burn from over-application or applying to dry soil. Flush the soil with plenty of plain water to dilute the excess salts.
Weak, Spindly Growth: Often a sign of over-fertilizing in low light conditions, like indoors during winter.

FAQ: Your Geranium Fertilizing Questions Answered

Can I use tomato fertilizer on geraniums?

Yes, you can. Tomato fertilizers are often high in potassium and phosphorus, which promotes flowering and fruit development. This nutrient balance is also excellent for encouraging blooms on geraniums, so it’s a good alternative if you have it on hand.

How often should I feed potted geraniums versus garden geraniums?

Potted geraniums need feeding more often because nutrients leach out of the drainage holes with each watering. Feed them every 2-3 weeks with a liquid fertilizer. In-ground geraniums have a larger soil area to draw nutrients from, so feeding every 4 weeks is usually adequate.

Is Epsom salt good for geraniums?

Epsom salt provides magnesium, which can help prevent yellowing leaves and might promote greener foliage. However, it is not a complete fertilizer. Use it as a supplemental treat once a month (1 tablespoon per gallon of water) in addition to your regular fertilizer, not as a replacement.

Should I fertilize geraniums in winter?

No. If your geraniums are dormant or growing very slowly indoors over winter, they do not need fertilizer. Feeding them during this time can harm the roots and cause poor growth. Wait until spring when you see new growth resume.

What’s the best time of day to fertilize?

The best time is in the early morning or late afternoon. Avoid fertilizing in the heat of the midday sun, as the combination of strong sun and fertilizer can stress the plant. Cooler times of day allow the plant to take up nutrients more effectively.

Getting the timing right for when to fertilize geraniums makes all the difference. By starting in spring with a balanced feed, switching to a bloom-booster for the summer marathon, and stopping in fall, you give your plants exactly what they need at the right time. Pair this schedule with proper watering and plenty of sun, and you’ll be rewarded with a spectacular display of vibrant, healthy blooms that last for months. Remember, gardening is about observation—watch how your plants respond and adjust your care slightly to suit there specific conditions.