Does Putting Plants in a Black Container Cause Them to Overheat in Summer? We Asked Gardening Pros

Key Points

Dark planters in full sun can overheat soil, harming roots and stunting plant growth.

Fuchsia, ferns pansies, most herbs, lettuce, and spinach will likely not survive summer heat in a dark black planter.

Dark pots can be useful in spring to warm soil for seed germination and early growth.

Dark-colored clothing certainly makes people warmer in the summer heat, but what about dark-colored planters for potted flowers and veggies? If your planter is black or navy and sitting in full sun rather than shade, you’ll want to read this—and protect your plants before it’s too late.

Below, a master gardener walks us through the dangers of using a black planter in summer, but she says there can also be times when a black plant container might be helpful to a gardener.

Meet the Expert

Alicia Lax has been a certified Master Gardener for 13 years and teaches container gardening and composting workshops in New Jersey.

Does Using a Black Container Harm Plants in Heat?

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The short answer is yes, using a black container in full sun can overheat your plants, master gardener and container gardening course instructor Alicia Lax says. The University of California’s Department of Agriculture and Natural Resources also warns against using metal pots or dark-colored planters.

The reason is because black planters (like our clothes) absorb heat and can raise the soil temperature above the ambient air temperature, Lax says.

In heat, temperatures in soil pots can reach 115 to 140°F. These high soil temperatures can slow or stop plant growth, increase fertilizer release, and damage or kill roots—or the entire plant.

“As a gardener, the one thing you’re really interested in is root development even before top development,” she says. “If you don’t have a good root system, you’re not going to have a good plant.”

Lax says the soil on the outside of the planter is warmest (though this is true no matter what color plant pot you pick), and dark metal containers for raised bed planting, for example, are especially harmful in heat.

That doesn’t mean you can’t have raised beds for summer. Lax says she loves raised bed planting; she has used resin both resin and wood for her own. She recommends either material for raised beds.

She also recommends seeking out self-watering pots and light-colored containers. Other researchers across the nursery industry push for light-colored containers, too, especially because garden center containers are often black plastic.

One nursery industry study at the Application Technology Research Unit in Ohio and the U.S. National Arboretum’s Floral and Nursery Plants Research Unit worksite in Tennessee found that using white pots instead of black reduced soil temperatures by 8 to 12°F and increased crop health and growth up to 130%.

How to Protect Your Plants from Overheating in a Dark Colored Planter

Lax says if you do have a dark planter you can’t part with, you could try nestling a plant in a light-colored planter within it, and fill the space between the two planters with perlite, which is white and reflective, or mulch.

“It’s going to put something in between the two pots and moderate the amount of heat that gets to the other pot,” she says.

A location with morning sun and afternoon shade is also a good idea as this will allow pots to remain cooler in the hottest part of the day. If you use large planters, you can use wheeled carts or plant stands to make them easier to move around during extreme summer temperatures.

You’ll also want to make sure your plant gets plenty of water.

When a Black Container Is Helpful

Lax stresses that dark-colored planters aren’t all bad in cooler climates or for early-season growing.

“In spring, when you want the soil to warm up and you want seeds to germinate or you want your transplants to take off, a darker pot might help you with that, so that’s not a bad thing,” she says.

What Plants Are Sensitive to Overheating in Certain Containers?

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Perennial or annual plants that prefer growing conditions in partial or full shade (such as hostas, impatiens, caladiums, or wax begonias) need cooler temperatures, and should not be placed where direct sun hits them in the late afternoon, when the sun is hottest and strongest.

Lax adds that fuchsia is “one of the more heat-sensitive plants” and will not do well in a black container; ferns will struggle in a dark container, and pansies won’t come back for fall if you go this route.

“In a dark pot in full sun, they probably will die on you,” she says.

Most culinary herbs (including thyme, oregano, cilantro, and dill) prefer mild temperatures and may wilt in too much direct sunlight, and the same thing is true lettuce and spinach.

“They have enough trouble under normal circumstances in heat, so in a dark pot, they won’t make it,” Lax says.

And succession planting in general will be difficult with a black planter in summer, Lax adds.

What Plants Might Survive in a Black Container?

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If you’re looking for something that has the highest chance of surviving in a hot black container, Lax recommends a chili pepper plant because they’re successful in hot climates, “but they also have their limits.”

Read the original article on The Spruce