Pro Tips For Estimating How Many Plants You Need

Estimating how many plants you'll need for your containers and garden beds isn't an exact science, but you'll come close if you follow these tips.

When spring arrives and you get the itch to go plant shopping, it’s tempting to buy way more than you have room for. There’s no exact formula for determining how many plants you need, and even experienced gardeners like me over-buy sometimes.

As an avid container gardener, I plant up more than 75 pots each year. My driveway transforms into a holding area as I gather plants from my local garden centers.

You’re bound to have a few extra or need to make at least one return trip to the store for more. If you’d like to be more strategic, I have some helpful tips to share with you.

Buy Within a Specific Color Palette

Select a palette of three colors for your container plants or landscape. Start there, and there’s a good chance you’ll find a place for whatever you bring home from the garden center. When you buy something that doesn’t fit your color theme, it can stick out awkwardly. Make a plan and follow it.

Understand Spread Versus Spacing

These two terms are commonly used interchangeably, but they’re not the same. Spread defines how wide a plant is expected to grow. Spacing describes how far apart to plant them if you’re growing multiples of the same item. If you want your plants to grow together, you’ll need to buy more than the spacing requirements indicate.

Decide How Quickly You Desire the Finished Look

Male customer purchasing plants from garden centerLuis Alvarez/Getty Images

For plants in containers and in the landscape, how many you need depends partly on how quickly you want them to fill the space.

For patio pots planted in the spring, you have plenty of time to watch them fill in, and it’s fun to see how they evolve through the season. If you’re getting a late start or planting fall containers, it’s best to start with more or larger plants to get that full look.

Landscape designer Mark Dwyer of Landscape Prescriptions by MD says, “Tight spacing does create challenges for access related to watering and weeding, but a tightly planted display of annuals also helps to shade the soil. That helps it retain moisture and minimizes weed competition.”

When planting perennials and shrubs in the landscape, have patience while they take a few years to fill in. You can start with larger specimens to speed up the process, but it’s likely you’ll need to mulch between them and keep up with weeding in the meantime.

Traditional-Style Flowerpots Use Fewer Plants

When planting annuals in containers in the spring via the general thriller-filler-spiller method, you can get away with fewer plants if you don’t mind waiting for them to fill in.

You’ll end up with healthier plants with plenty of root space and better air flow throughout, which reduces the incidence of pests and diseases. Planters potted in this manner are more likely to last all season because the plants aren’t overcrowded.

For traditional 10- to 12-inch flower pots: Fill with three to four annuals of average vigor (geraniums, verbena, calibrachoa), two extra-vigorous plants (Dragonwing begonia, Supertunia Vista petunias, coleus), or a one-gallon potted perennial or shrub.

For traditional 14- to 16-inch flower pots: Fill with four to six annuals of average vigor, three extra-vigorous plants, or a single one or two-gallon potted perennial or shrub.

For traditional 16- to 20-inch flower pots: Fill with six to eight annuals of average vigor, four extra-vigorous plants or a single two- or three-gallon potted perennial or shrub.

Florist-Style Flower Pots Use More Plants

If you prefer your containers to look full immediately after planting — say, for an upcoming party — start with more plants. Choose this style if the plants won’t have much time to grow, e.g. in September for the fall season. Pre-planted combination containers you buy at the garden center are usually planted in the florist style.

Besides the added expense, there are a few downsides to consider.

Because there is more root competition and plants are competing for space, the soil will dry out faster and you’ll need to water these containers more frequently. You’ll also need to prune out selective stems or even remove entire plants as the planter fills in and the more vigorous varieties in the mix start to dominate.

A full container also needs to be fertilized more often because there are more plants competing for the available nutrients.

Use a Plant Calculator for Garden Beds

Plant spacing calculators are helpful when filling an empty space with all one kind of plant, like a ground cover, or several types that grow to a similar size. Garden Crossings’ plant calculator is easy to use. Your local garden center’s website may have one, too.

You’ll need the length and width measurements of your space, as well as the plant’s spread. The tool automatically calculates how many plants you need to fill the space. Unfortunately, this kind of tool is less helpful if you’re mixing several sizes of plants, or if your space is an odd shape.

Estimate Number of Plants for Hedges

Figuring out how many plants you need to form a hedge is simple, as long as you’re willing to wait for them to fill in. Patience is key when planning a new hedge.

Many people desire instant privacy and space the plants too close together. Such hedges become more prone to pests and diseases due to overcrowding, and often need to be replaced far sooner than if the plants had been properly spaced at the start.

Horticulturist Kristina Howley of Spring Meadow Nursery reminds us to closely evaluate spacing when planting a hedge. Typically, a plant label will list a range, like four to six feet.

“Use the plant’s mature spread to help inform your spacing decisions,” she says. “If you’d like a solid hedge with few gaps, go with the smaller end of the recommended spacing range. If you don’t want the plants to touch or want an airy look, use the larger end of the spacing range.”

Hedge plants can be pricey and not all nurseries let you return them. Check your store’s return policy before purchasing.

Fewer is Better When Spacing Vegetables

It’s important not to overcrowd your vegetable gardens. You’ll likely need fewer than your enthusiastic self really wants to buy in the spring. You may not need all of the seeds that come in the packet, either. Save a few for staggered sowings instead.

“Most vegetables like to have ample space to grow and good air circulation around the plants is a must,” Dwyer says. “Follow the thinning suggestions on the plant tag or seed packet especially for root vegetables like carrots and radishes.”

If you overcrowd your carrots, they won’t grow long and straight. Crowded vegetables generally produce a smaller harvest. Instead, Dwyer recommends maximizing your space with successive sowings and rotating your plants around the garden from year to year for best success.

Susan Martin
Susan Martin is a prominent and prolific Michigan-based garden writer, speaker and coach who enjoys sharing her passion for plants, gardening and the business of horticulture with fellow plant enthusiasts across North America. She has spent over two decades working in horticulture in new plant development, garden design, sales, marketing and consulting. Susan has received visitors from around the world in her home garden which has been featured in numerous publications. Her goal is to inspire and educate people about how to garden every day.