I've fielded countless questions about planting in planters and pots: Which container should I choose? What potting soil is best? How much drainage material do I need at the bottom?
Container gardens on balconies, terraces, and window sills remain a popular choice, and rightly so—they bring vibrant life to small spaces.
Based on years of hands-on gardening experience, here's a reliable summary of best practices.
Planting in a Medici vase
The choice depends on your plants. For bedding annuals like lobelia, petunia, carnations, marigolds, surfinia, diascia, begonia, bidens, cleome, celosia, and herbs such as parsley, chives, thyme, or mint, standard window boxes work well. Regular fertilization is still essential for best results.
For budget-conscious gardeners, repurpose terracotta chrysanthemum pots from cemeteries—they're often the ideal size for annuals and herbs. Even slightly cracked ones can be paired up for stability.
Larger shrubs and perennials need more root space, so opt for containers 40-70 cm deep and equally wide.
Drainage is non-negotiable. Always include a layer of gravel, pozzolan, clay balls, broken pot shards, or coarse gravel at the bottom. Without it, water won't drain properly, roots suffocate from poor aeration, and your plants suffer—far from the ideal conditions they enjoyed in the nursery.
Aim for 2-15 cm of drainage material, depending on pot height, leaving ample room for soil above.
Potting soil (or substrate) must match your plants' needs. Skip cheap "horticultural compost"—it's a false economy that leads to frequent replanting, as I've learned from experience.
For ericaceous plants like azaleas, rhododendrons, or ferns, use heather soil. Citrus trees need citrus mix; orchids, cacti, geraniums, and flowering plants require their specific blends. Choose mid- to high-quality ready-to-use options.
Read more about selecting potting soil here.
Modern planters often list their volume—helpful! Otherwise, calculate: width × length × height (in meters).
Example: A 20 cm wide, 70 cm long, 15 cm high planter is 0.20 × 0.70 × 0.15 = 0.021 cubic meters, or 21 liters (1 m³ = 1000 liters).
For round pots: π × r² × h. Example: 40 cm diameter (r=0.20 m), 50 cm high: 3.14 × 0.20² × 0.50 = 0.063 cubic meters, or 63 liters.
Alternatively, use cm and divide by 1,000,000 for liters.
Fertilization is key to healthy, vibrant plants. Opt for organic fertilizers over cheap chemical ones. Follow label instructions for doses and frequency.
See my fertilization tests here.
Topiary in a tray
"How often should I water?" It varies by temperature, wind, plant stage, size, variety, and exposure—just like your own hydration needs in summer. Observe your plants closely and water before they wilt. With practice, you'll get the rhythm right.
If your budget is €100, allocate €50 to the plant, and the rest to quality pot, soil, drainage, and fertilizer. What flowers do you love in your containers?
