That's a very smart question to ask! The weight of filled planter boxes is a crucial safety consideration that many urban gardeners overlook. A balcony's structural integrity depends on you not exceeding its weight capacity.
So, how heavy are they? The total weight is a combination of the planter itself, the soil, and the water it holds.
Let's break it down. First, consider the empty planter. A lightweight plastic or fiberglass box might weigh 5-10 lbs (2-4.5 kg), while a ceramic, concrete, or wooden planter can easily weigh 20-50 lbs (9-23 kg) or more on its own.
The real weight, however, comes from the soil. A cubic foot of dry potting soil typically weighs between 40 and 50 pounds (18-23 kg). When you saturate that soil with water, the weight can increase significantly—by as much as 20 pounds (9 kg) or more per cubic foot.
A Practical Example:
Imagine a common rectangular planter box that is 2 feet long, 1 foot wide, and 1 foot deep. This gives it a volume of 2 cubic feet.
* Weight of empty resin planter: ~10 lbs (4.5 kg)
* Weight of 2 cubic feet of dry soil: ~90 lbs (41 kg)
* Total Dry Weight: ~100 lbs (45 kg)
* After a heavy watering, add another 20-40 lbs (9-18 kg) for water.
* Total Saturated Weight: ~120-140 lbs (54-64 kg)
As you can see, just one moderately sized planter can be very heavy. Two or three of them can quickly add several hundred pounds to your balcony.
How to Garden Safely on Your Balcony:
1. Know Your Balcony's Limit: Check your building's guidelines or contact your landlord. Most modern balconies are designed for loads of 40-50 pounds per square foot (psf).
2. Choose Lightweight Materials: Opt for planters made from plastic, fiberglass, or metal. Avoid concrete and thick ceramic.
3. Use Lightweight Soil Mixes: Look for potting mixes that contain perlite, vermiculite, or coir. These provide excellent drainage and are much lighter than topsoil or garden soil.
4. Distribute the Weight: Place your heaviest planters over the load-bearing wall or support beams, typically against the wall where the balcony attaches to the building. Avoid concentrating all the weight in one spot.
5. Consider Smaller Containers: Several smaller, lighter pots are often easier to manage and distribute than one massive, heavy planter.
By calculating the weight and choosing your materials wisely, you can create a beautiful and, most importantly, safe balcony garden.