How and Why to Fertilize Your Flower Garden

Flowering plants cannot flower without the right nutrients, making fertilizing an essential part of flower garden care. Gardening expert Madison Moulton explains the importance of fertilizers and how to fertilize your flower garden.

A colorful garden overflowing with flowers and plants. Tall green shrubs line the left side of the garden, while shorter plants with pink, purple, and white flowers fill the foreground. There are also several small trees in the background, which provide shade and help to create a sense of depth.

A lush flower garden is truly incomplete without an essential component – the flowers themselves. There are many factors that contribute to an abundant flower garden overflowing with blooms, and fertilizer is one of them.

Feeding is not really a ‘one size fits all’ task. How and when you fertilize, as well as what you use to fertilize, will depend on the season and the specific plants you are growing. But there is no doubt that fertilizer is important, and these general guidelines will help you decide on the best course of action for your flower garden.

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Plant Nutrients Explained

A close-up of a white, open bag of fertilizer filled with small, round, brown fertilizer pellets. Sunlight glints off the smooth granules, highlighting their texture. A bright green plastic scoop rests nestled within the pile, ready for scooping.
Macronutrients like nitrogen, phosphorus, and potassium (NPK) support plant growth, ensuring health and vitality.

As avid gardeners know all too well, nutrients play a vital role in plant growth and overall health – much like humans. Nutrients, along with water and light, are the resources that support everything from root development to flower formation.

The three primary macronutrients are nitrogen (N), phosphorus (P), and potassium (K). That’s why you’ll see the abbreviation NPK on fertilizer packaging.

Nitrogen is essential for leaf and stem growth and is the main component responsible for giving leaves their lush green color. Phosphorus supports the development of roots and flowers. Potassium enhances overall plant health, aiding in water regulation and the synthesis of important plant compounds. While they have somewhat individual functions, these nutrients largely work together to ensure all parts of the plant function correctly.

Beyond these macronutrients, plants also require secondary nutrients like calcium, magnesium, and sulfur and a range of micronutrients, including iron, zinc, and boron. But don’t let the terms ‘secondary’ or ‘micro’ fool you. These elements, though needed in smaller quantities, are equally vital for plants and can cause serious problems if there are deficiencies.

When plants lack these necessary nutrients, they will tell you with a few symptoms. These range from yellowing leaves to weak stems and slow growth. You may also spot browning at leaf edges, often caused by potassium problems. It’s important to stay on top of nutrient monitoring in the soil to ensure you don’t have to tackle any of these issues later on.

Why Fertilizer Is Important

A close-up of a pile of dark brown soil filled with small, bright blue-green balls of fertilizer. The soil looks moist and healthy, and there are small pieces of organic matter and fibers visible throughout.
Plants absorb nutrients from the soil through roots, but soil depletion occurs over time.

All plants absorb nutrients from the soil as they draw up moisture through their roots. From here, the nutrients get transported around the plant to the parts that need it. But soil can slowly lose nutrients over time, becoming depleted as plants use them and leaching away whenever you water. The effect is more prevalent in containers as there is limited soil and much more frequent watering.

That’s where fertilizer comes in. To counteract this potential depletion, we can make use of fertilizers to ensure nutrient levels never dip too low. They replace lost nutrients and ensure that the soil remains fertile and conducive to plant growth.

Building overall soil health is important, but fertilizers are a great quick fix, especially when you’re dealing with ‘hungry’ plants that grow quickly and absorb more nutrients than others to fuel growth.

Flowering plants can be considered part of the ‘hungry’ category because they generally require a significant amount of resources to produce blooms. Regular feeding fuels the flowering process to encourage healthy blooms as long as the season allows.

It’s important to remember that not all plants have the same nutrient needs. Some plants may thrive with higher nitrogen levels, while others might need more potassium or phosphorus. However, since the latter two nutrients are the most responsible for flower development, any fertilizer slightly lower in nitrogen is usually good for most flowering plants (at the time of flowering).

When To Fertilize Your Flower Garden

A close-up shows a gardener’s gloved hands holding a handful of fertilizer next to a red petunia flower in full bloom. The cyan-colored gloves cradle the granules, while the vibrant red petals of the flower stand out against the dark soil in the pot.
Tailor fertilizer application to your flower garden’s needs, adjusting based on growth stages and climate.

The ideal time to fertilize your flower garden will depend on your climate and what you’re growing.

Since spring is considered the season of flowers, this is usually the time feeding starts, continuing throughout summer and often in fall in milder climates. But it’s important to understand the needs of the specific plants you’re growing to fertilize at the right time.

Different times of the season also call for different types of fertilizers. If your plants have just gone into the ground, a balanced fertilizer is usually best because they’ll start with leaf and stem growth, requiring more nitrogen. Later in the season, you can adjust the nutrient ratios to better support flowering.

For forgetful gardeners like myself, establishing a feeding schedule is a helpful way to catch nutrient deficiencies before they pop up. If you have a garden journal, add your next fertilizing date there or pop it into your cellphone calendar.

It’s important to keep monitoring your plants, as they may need feeding slightly more or less often than a schedule allows. But this will ensure you don’t forget feeding altogether.

How To Fertilize Your Flower Garden

A close-up of a glass test tube filled with a soil sample. The soil in the test tube and in the background is very dark, moist, and crumbly. There are also small pieces of organic matter visible in the soil.
Conducting a thorough soil test is strongly recommended as a preliminary step before initiating any fertilization regimen.

Before you start any feeding, it’s recommended to test your soil. It may seem like an extra unnecessary chore, but a soil test can help you identify any possible deficiencies that dictate what fertilizer you should choose. Alternatively, you can consider what has grown in that area in the past and how the plants performed to decide what nutrients may be more depleted.

Next, choose a fertilizer that matches the needs of your flower garden at that point in the season. Flower fertilizers contain higher amounts of phosphorus and potassium, but this may not be ideal first-thing in spring when leaf and stem growth is the priority to support a mass of flowers later on.

There are also different fertilizer types to consider, from liquid to slow release. These are absorbed slightly differently but generally achieve the same goal. As long as you follow the instructions on the packaging exactly, you shouldn’t have any problems.

Continue to feed according to the timing and application method recommended on the specific product you’ve chosen. Adjust your feeding as your flower garden grows to provide the right nutrients at the perfect times. Always avoid getting fertilizers directly on the leaves and stems as this can lead to damage. Focus the product around the soil where it’s most useful.

Keep up with watering alongside feeding to ensure the plants absorb all the available nutrients. If your fertilizer granules are sitting on top of dry soil, there is no way for the nutrients to be carried to the roots.

Signs of Underfertilizing

If you’re not confident about feeding times, it’s helpful to understand the signs of underfertilization in plants. Many of these signs can also be caused by other growth problems, so make sure you identify nutrients as the real cause before you use fertilizer as a quick fix. If an imbalance is not the issue, feeding when the plant is stressed can exacerbate the problem.

Stunted Growth

Close-up of a pepper plant showcasing telltale signs of stunted growth and low pepper production. Numerous leaves appear significantly smaller than expected, tightly curled at the edges, and wrinkled, suggesting the plant is under significant stress.
Stunted growth and slowed plant development may signal essential nutrient deficiencies.

If plants are not growing to their expected size or at their usual rate, it could indicate a lack of essential nutrients. Weak leaves and stems are also a sign of a potential nutrient problem – usually a lack of nitrogen or potassium. Other possible causes include lack of sunlight, incorrect watering, or pest and disease problems.

Pale or Yellowing Leaves

Insufficient nitrogen results in pale or spotty yellow leaves.

Nitrogen is a key in the formation of chlorophyll, giving plants their green color. When there is not enough nitrogen, leaves lose this color and can become pale or a spotty yellow.

Yellow leaves are also caused by over or underwatering and pest damage, among other things. Assess soil health first before adding a high-nitrogen fertilizer.

Poor Blooming

Close-up of an ornamental plant struggling to bloom. Tight purple flower buds sit atop long, narrow leaves in a concrete planter. Sunlight falls on the pot, highlighting its isolation against a backdrop of lush green foliage.
Nutrient imbalance can result in smaller or fewer flowers and, in extreme cases, a complete absence of blooms.

In a flower garden, the last thing you want to see is a lack of blooms. Insufficient nutrients are a likely cause, particularly when it comes to phosphorus.

A nutrient imbalance may lead to small flowers, fewer flowers, or worse – no flowers at all. Regular flower garden fertilizing will help prevent this.

Signs of Overfertilizing

Although you may assume extra feeding will only lead to better and stronger growth, the opposite is actually the case. Overfertilizing is damaging to plants, causing a range of symptoms that you should look out for soon after feeding.

These issues are also tough to rectify, so it’s best to avoid them altogether by following the instructions on the packaging clearly and never feeding more than necessary.

Leaf Burn

A close-up of an anthurium plant with several diseased leaves. Some of the leaves are brown and curled, while others are yellowing or just starting to turn brown. The edges of some of the leaves are also crispy and dry hinting at underwatering, overwatering, or root rot.
Excessive fertilizer causes burnt roots and leaves, leading to irreversible damage with brown, crispy edges and tips.

When plants are overfertilized, the roots and leaves can essentially become burned. You’ll notice leaf edges and tips turn brown and crispy soon after feeding. This is caused by an excess of fertilizer that damages the plant tissue, and this plant tissue won’t return to normal once it dies off.

Crust on Soil Surface

Too much fertilizer can lead to a crusty coating of salt on the soil surface.

If you feed too often, a white crust of salts can build up on the soil surface, impacting moisture absorption in the plants. You may also notice some wilting and yellowing due to this lack of moisture.

Final Thoughts

If you want your flower garden to overflow with blooms, fertilizing is a crucial part of care. Choose your fertilizers carefully and apply them according to instructions to avoid any accidental over or underfertilizing.

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