window box failure - Ask Extension
I have had south facing wooden window boxes for decades. For the past several years no matter what I plant, they start out strong but by the end of Ju...
Knowledgebase
window box failure #928187
Asked April 12, 2026, 7:50 PM EDT
I have had south facing wooden window boxes for decades. For the past several years no matter what I plant, they start out strong but by the end of June the flowers start dying out. One year I’ll plant full sun annuals and when they fail, the following year I’ll try shade loving annuals. Last year I planted impatience and torenia and the impatience leaves turned a rust color. I have tried replacing the soil each year with the same results. Could my wooden window boxes be contaminated? I’m not sure what to plant this year. I’d appreciate any advice you could provide. Thank you.
(The photo attached is from June 2025. As you can see, they’re already starting to go.)
Baltimore City County Maryland
Expert Response
Contamination should not be an issue. Environmental conditions like sunlight level, soil moisture fluctuations, and nutrient availability are likely factors behind the problem.
How much sun in summer does the box get? A southern exposure isn't necessarily full sun unless there's no building or tree obstructing the light, and if any nearby trees have grown enough in that time to start shading the box when they didn't used to, that can impact how vigorous certain plants will be over the season.
Are the plants fertilized throughout the season? (Such as with a slow-release granular/pelleted fertilizer or a liquid fertilizer?) The plants in the photo look a bit nitrogen-deficient, which suggests they aren't getting enough nutrients over the course of the season, since whatever might be in fresh potting mix gets used-up or leached out after a while. Window boxes tend to hold small volumes of soil and would need frequent watering once it stays hot, which leaches out nitrogen faster than it would be used-up on its own.
If it's a hot, full-sun exposure that is prone to getting dry, Portulaca, Lantana, and flowering Sage might fare better in terms of dealing with heat and drought stress. If it's semi-shade, Impatiens (including New Guinea Impatiens), Torenia, plus Fuchsia and Caladium should do fine as long as they don't get under- or over-watered and are periodically fertilized (how often greatly depends on what kind of fertilizer is used; refer to the product label for dosage instructions).
Spite mites can cause leaves to turn pale or bronzy when populations are high and causing lots of damage, but we don't often see them on Impatiens, and their silken webbing usually becomes quite noticeable when populations are at that point. Some fungal diseases can damage annual flowers or foliage if they are too crowded and don't get good air circulation, but that doesn't tend to cause a rusty leaf color.
Miri
How much sun in summer does the box get? A southern exposure isn't necessarily full sun unless there's no building or tree obstructing the light, and if any nearby trees have grown enough in that time to start shading the box when they didn't used to, that can impact how vigorous certain plants will be over the season.
Are the plants fertilized throughout the season? (Such as with a slow-release granular/pelleted fertilizer or a liquid fertilizer?) The plants in the photo look a bit nitrogen-deficient, which suggests they aren't getting enough nutrients over the course of the season, since whatever might be in fresh potting mix gets used-up or leached out after a while. Window boxes tend to hold small volumes of soil and would need frequent watering once it stays hot, which leaches out nitrogen faster than it would be used-up on its own.
If it's a hot, full-sun exposure that is prone to getting dry, Portulaca, Lantana, and flowering Sage might fare better in terms of dealing with heat and drought stress. If it's semi-shade, Impatiens (including New Guinea Impatiens), Torenia, plus Fuchsia and Caladium should do fine as long as they don't get under- or over-watered and are periodically fertilized (how often greatly depends on what kind of fertilizer is used; refer to the product label for dosage instructions).
Spite mites can cause leaves to turn pale or bronzy when populations are high and causing lots of damage, but we don't often see them on Impatiens, and their silken webbing usually becomes quite noticeable when populations are at that point. Some fungal diseases can damage annual flowers or foliage if they are too crowded and don't get good air circulation, but that doesn't tend to cause a rusty leaf color.
Miri
