Why You Should Consider Wrapping Your Planters In Aluminum Foil During Summer

Container gardening has its charms and its challenges. In the heat of summer, keeping the soil in a pot moist can be a challenge, which contributes to another problem you might not have thought of. Container soil can be susceptible to very high temperatures, which can stunt growth or cause unwanted bolting of crops like summer lettuce. YouTuber and carnivorous plant aficionado The Flytrap Garden is trying to propagate and care for some South American Drosera, also known as sundew, species, and noted that their native habitat was much cooler than the environment he was providing. His solution was simple and effective: wrap the planters in aluminum foil.

This trick works because aluminum is very efficient –- as much as 97% –- at reflecting radiant heat. It has become common to see foil or aluminum coatings on insulation facing because it dramatically reduces the amount of heat that radiates into surfaces. Wet soil is more resistant to temperature fluctuations, so keeping your plants watered will help as well. While foil is an effective radiant barrier, it won't have much impact on the conductive transfer (through solids) or convective transfer (through gases and liquids) of heat. So if the air, work tables, etc. in your greenhouse are 120 degrees, aluminum foil won't stop that heat from reaching your plant's soil. The proper response when radiant, convective, and conductive heat are all too much for your plants is to make the environment cooler or move the plants.

Some concerns about aluminum and plants

Because his Drosera is grown in trays of water (their natural environment is usually wetlands), The Flytrap Garden expressed some concerns about aluminum leaching from the foil into his potting soil. Soil acidity is a significant problem. About 30% of Earth's land surface and 40% of its arable soil is acidic, resulting in land that can't be farmed – including land that was once used to grow crops. Some plants thrive in acidic soil, but many do not. Aluminum toxicity contributes to root growth issues in plants in acidic soil. Since Drosera are grown in mildly acidic soil, the YouTuber might have cause to be concerned. Aluminum can certainly leach into water, at sufficient temperatures or water acidity. Water boiled in six-year-old aluminum pots has been shown to contain as much as 5 times the World Health Organization's standard for aluminum content, and acid rain is known to cause aluminum leaching, which can harm plants and soil.

That said, The Flytrap Garden probably doesn't have a lot to be concerned about. Acid rain has a pH in the range of 4.2 to 4.4, which is far more acidic than tap water. And it's equally unlikely that he'll be boiling six-year-old foil as part of his watering regimen. Playing it safe, he trimmed the foil above the water line in his trays. Since the underwater part of his pots are more likely to absorb heat by convection anyway, there's no harm in this precaution.