Planting in a window box seems simple. But a few basic habits make all the difference in the long run. Here is how to do it, step by step.
A well-planted window box is one that produces, blooms, or stays beautiful for months. A poorly planted window box often results in plants that stagnate, yellow, or wither for no apparent reason. The difference rarely lies in the plants chosen; it almost always comes down to the preparation of the container.
What to gather before you start
Before opening the bags of potting soil, gather your materials: a bag of clay pebbles or gravel for drainage, potting soil suited to the chosen plants, the plants or seeds, and a watering can with a fine rose. Extra Terrasse window boxes come with six drainage holes already drilled in the bottom: there is nothing to do there. For any other window box that doesn't have them, drill them first. Without a way for excess water to drain, roots will rot within a few weeks, even with moderate watering.
The drainage layer: a step you shouldn't skip
At the bottom of the window box, lay down a 3 to 5-centimeter drainage layer: clay pebbles, gravel, or stones. This layer prevents roots from sitting in stagnant water, which is the primary cause of plant mortality in containers. It is a simple habit that takes two minutes and makes a real difference to the lifespan of the plants.
Choosing the right potting soil according to the plants
Standard universal potting soil is suitable for the majority of window box plantings. However, some plants have specific needs. Mediterranean plants like rosemary, thyme, and lavender prefer a well-draining, low-nutrient substrate: mix universal potting soil with one-third coarse sand. Strawberries and tomatoes appreciate soil enriched with compost. Cacti and succulents require a very well-draining substrate with little organic matter. Investing in two or three types of potting soil rather than just one for everything really changes the results.
If you are in doubt: we recommend choosing a classic potting mix.
Planting and spacing correctly
Fill the window box two-thirds of the way with the substrate before planting. Place the plants while respecting the distances recommended on the labels: if they are too close together, they will compete for water and light. Fill in with potting soil up to two centimeters below the rim of the box to leave room for watering without overflow. Tamp down lightly around each plant to eliminate air pockets.
Initial watering and first care
Right after planting, water generously until water begins to drain from the holes. For the first few days, monitor soil moisture by sticking a finger two centimeters deep into the soil. In summer, most railing planters need daily watering in the morning, especially in full sun. In autumn and winter, reduce watering significantly: plants grow slowly and consume much less water.
In summary
Drainage, good soil, proper spacing, and generous initial watering. These are the four foundations of a well-planted window box. With these basics respected, the vast majority of container-friendly plants will thrive without difficulty.