Flower Boxes: 5 Mistakes Everyone Makes

White flower box with a variety of annual flowers

If you want gardening ideas, flower boxes can tick up your landscape. Nicely planted flower boxes add a touch of elegance to windowsills, balconies, and almost any garden space. But it's not as simple as picking up some flowers and dropping them into the box.

You must plan things to get the most from your flower window boxes. Plus, you must avoid common mistakes that prevent them from looking their best. These same mistakes apply to over-the-railing planters.

Let's look at mistakes people make to ensure your flower boxes flourish.

Mistake #1: Choosing the Wrong Size Flower Box

Regarding flower boxes, it's not a one size fits all proposition. Ever bought size eight shoes but needed size 9? Uncomfortable experience.

Well, the same thing holds for your flower boxes. To attract attention with colorful plants, they need room to grow. A flower box that's too small causes root binding. Your plants will struggle for space, stunting their growth.

On the other hand, a larger container might hold too much water, increasing the risk of root rot. Plus, your flower box could wind up looking empty.

Sage green flower box with colorful flowers

What's the Right Size Planter?

You can pick up flower boxes in a range of sizes. Many start at 18 inches and work their way up to as big as 36 inches.

Let's say a 24-inch box will fit your space perfectly. Consider that most plants grow three to four times larger throughout the season. So, you'll want to target planting five to seven plants in that 24-inch flower box. The key is keeping in mind the mature size of your favorite flowers.

Some folks are impatient. They don't want to wait a month or so for their flower box to fill out. You can put more plants into your planter if you're one of them. But you'll have to pinch them to keep them from overcrowding.

If you want to avoid guesswork, there are plant calculators to help you determine the perfect number.

Mistake #2: Poor Drainage

We all need water to survive. But for plants, too much water can kill them. That can happen in several ways:

  1. You get so concerned about under-watering that you overwater (more on that briefly).
  2. You grab a shovel and use ground soil in your planter. Ground soil compacts and can become a water-retaining brick. Use a quality potting mix that keeps the dirt loose so it drains.
  3. Your flower box doesn't have drainage holes, or you forget to open them.

I've been guilty of that last gardening mistake. I planted a gorgeous, salmon-colored geranium. It was lush with flowers, and several guests commented on how beautiful the flower was.

Unfortunately, it began to wilt and die back. Initially, I thought I needed to water it more. So I watered it more, and it died back more.

It was only until I looked under the flower box that I found the issue. The drainage plugs were still there. I removed them, and my geranium returned to its full glory with proper drainage.

Tell-Tale Signs of Drainage Issues

When you overwater your floral arrangements, it's like killing your plants with kindness. You mean well, but it's not always the best. I was guilty of that.

Fortunately, there are some tell-tale signs if you're using too much water:

  • New and old leaves are falling off at the same time
  • Leaves are brown, yellow, and wilting
  • Leaves, stems, or flowers are moldy
  • Leaf tips are brown
  • Root rot or foul odor
  • Grey and slimy roots

Mistake #3: Improper Watering

Drainage and watering go hand-in-hand. Proper drainage sets the stage for proper watering. You've already learned what too much water can do to a plant, whether it's from no drainage or watering too much.

Giving your plants too little water in a flower box has a similar detrimental impact.

The Thirsty Plant Syndrome

If you give your plants too little water, they can exhibit similar signs to over-watered plants. Leaves can wilt, turn yellow, and fall off.

But there are other signs:

  • Droopy or folded leaves
  • Leaves turn brown
  • Plant growth slows
  • Leaves that feel paper-thin and crispy
  • On succulent plants, leaves that look wrinkly
  • Dried out roots

Apart from your plants, you can also gain insight by looking at your container's soil. First, the soil will get hard and dry. Second, you might see a gap between the soil and the flower box walls.

Remove the Guesswork from Watering

Black flower box with purple flowers

Whether new to gardening or a veteran, watering is often a significant concern. Fortunately, you can cut the guesswork by using a self-watering flower box.

Self-watering flower boxes have a reservoir at their bottom. That reservoir delivers water to your plants through capillary action. And that offers an assortment of benefits to gardeners.

  1. Self-watering planters retain moisture. They provide plants with the right amount of water as needed.
  2. They ensure a steady water supply of water. Maintaining a consistent water balance keeps plant roots healthy.
  3. Consistent water reduces plant stress. So you'll get more vigorous, vibrant plants.

As important, you no longer have to worry about killing your plants. The self-watering planter does all the work for you. So both you and your plants are happy.

You can also consider installing a drip irrigation system. That's especially helpful if you have several flower boxes in a similar location.

Mistake #4: Ignoring the Sunlight Requirements

Another common flower box mistake is placing it in the wrong location. Now, of course, you can put a flower box anywhere. But you can't choose plants for a flower box and put them anywhere.

You have to select plants based on sunlight requirements. Simply, sun-loving plants need six or more hours of daylight. Shade-loving plants can get by with four hours or less sunlight.

So you can create a sunny flower box using perennials or annuals. And there's no limit to what you can include:

  • Geraniums
  • Marigolds
  • Black-eyed Susans
  • Coneflowers
  • Salvia
  • Snapdragons
  • Dahlias

White flower box liner with pink flowers on railing post

The list goes on and on. Similarly, you can create a shade-loving flower box using coleus, begonias, impatiens, or fuschia, to name a few.

What you can't do is mix them or place them in the wrong location.

Reading the Sunlight Signs

Excessive sunlight harms flower box plants, causing leaves to wilt, turn yellow or brown, and develop scorched or bleached patches. Leaf scorching is usually the most obvious sign. Plus, if your soil dries out quickly, it's a good bet there's too much heat and sunlight.

Too little sunlight causes leaves to brown or stunts their production. You'll also notice plants getting leggy or leaning toward a light source. Variegated plants often lose their variegation. They'll revert to a solid color.

And whereas too much sun causes soil to dry quickly. Too little sun results in consistently damp soil.

Mistake #5: Poor Flower Arranging

This common mistake won't necessarily impact your plants and their health. But it will affect how attractive your flower box looks or doesn't look.

Creating a stunning flower box requires some planning. Otherwise, it can look like a jumble where nothing captures your attention.

The Thriller-Spiller-Filler Approach to Flower Boxes

If you're new to gardening, you might have yet to hear of the thriller-spiller-filler concept. It's the perfect way to approach planting any planter.

Thriller plants drive the flower box design. They create the backdrop and primary interest. So start with taller, colorful plants. For example, taller geraniums or coleus give you the necessary height and color.

Next, think about your spiller plants. They'll drape over the sides of your flower box to soften its edges and add depth. Spiller plants include ivy, petunias, calibrachoa, and creeping jenny.

Finally, add some filler plants to round things out. As it implies, filler plants nestle between the thriller and spiller plants for balance. First, ensure they're shorter than your filler plants to avoid competition. Second, you use filler plants to add texture or balance your colors.

For example, consider adding green plants for contrast if you use colorful plants for your thriller and spiller plantings. Plants that contribute texture include coral bells, smaller ferns, hens and chicks, euphorbia, and stonecrop.

Decorative Planters from Root & Vessel

Different colors of flower boxes

If you want to add flower boxes to your garden collection, we have four sizes in five colors. So you can find the right size and look to complement your style. We also have self-watering flower boxes from Artstone.

No matter what decorative planter you select, we back it with our 100% guarantee. Check out our photo gallery for inspiration and ideas on how other gardening enthusiasts use our planters.