So if you’re new to window boxes and are going through your first summer there are a few things you need to know. Watering can be a big deal, especially if your window box gets direct sun exposure instead of shade. This could even affect which plants and flowers you should choose to plant and which ones will perform well in a window box, so make sure to assess your home and the windows you plan to use for window boxes. Flowers that need a lot of water or prefer shade could under perform in a summer window box or have trouble growing.
Picking Good Flowers for Direct Sunlight
When you’re at the garden nursery it’s a good idea to not just grab flowers that look pretty, but to actually read the labels. Most flowers will say things like “full sun, partial sun, or shade.” This will indicate the ideal requirements for these plants and flowers and will help you avoid picking flowers that will be hard to upkeep or dry out easily. I’ve made the mistake of grabbing flowers that were ideally suited for shade in a window box that gets direct sun and found that if they were not even watered for a day they would completely droop over and on the flip side of things I’ve picked flowers that do well in direct sun and forgotten to water them for a whole week with almost no side effects. So this is a big part of the equation which is understanding which plants will automatically do well for your particular window and balanced with the amount of time commitment you will have.
Watering Basics for Summer Window Boxes
Flowers and plants will require much more watering than you’re used to. For an outdoor window box you need make sure drain holes are present so that rain doesn’t fill up the box which could drown out the roots. Once this is done your main adversary will be making sure the window box gets enough water, as under watering tends to be the biggest challenge. This is directly opposite of when you’re dealing with indoor planters and you need to be careful not to water too much because they don’t typically have good drainage. If you’re worried about the drainage leaving dirt stains on the house a simple solution to this is laying a thin layer of landscape fabric on the bottom of the box and putting your potting mix on top of that. This acts as a layer of filtration and helps prevent clumps of soil from falling out the box essentially filtering your water and dirt out. You can also use a thin layer of pea gravel instead if you already have it.
Ways to Prevent Window Boxes from Drying Out
Here are some considerations to make sure you’re window boxes are getting enough water. Use a high quality potting mix with perlite to help aerate the soil and retain moisture. If the mix doesn’t have perlite you can add water absorbing polymers like “Soil Moist” and mix into your potting mix to help. This will help the soil retains more of it’s moisture. If you’re using a hanging basket then coco fiber will help retain moisture, but also try to use as much soil in the box as possible. Maximize your soil capacity as the more soil in the box the better it will shield the moist soil at the bottom from the sun and the less frequent you will be watering. If you can purchase a deeper window box it will help in direct sun situations. For example, a 10” tall window box can retain a lot more water than an 8” tall window box. Be prepared to water twice as often as you did in the spring, perhaps even daily, or your flowers could get very dry and wilt.
Consider running a drip line or sprinkler to the window box or even using a window box self-watering reservoir to increase your water capacity and help reduce your watering frequency. There’s a lot of good products on the market. Some use tubes to direct water to the box from an outdoor spigot while others are fully contained inside the box and don’t have unsightly water lines dangling on the outside of the home.
About the Author Matt Buquoi is the owner of Flower Window Boxes, Inc. He has over a decade experience in the container gardening industry helping customers of all levels of experience.