Window Box Garden Cost Calculator

Budget your window box before buying plants.

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Frequently Asked Questions

What size window box do I need?
Match the box length to your window width or rail span, leaving 2-4 inches on each side. Depth matters more than length: aim for at least 6-8 inches deep so roots have room and the soil doesn't dry out in an hour. A 24-inch box is the most common size and works for 5-6 standard plants.
Can I reuse potting mix from last year?
You can refresh old potting mix rather than fully replacing it. Remove any dead roots, add about 25-30% new mix by volume, and blend in a fresh dose of slow-release fertilizer. Replace entirely if the mix has shrunk significantly or if you had disease problems the previous season.
How often do window boxes need watering?
In warm weather, daily watering is common - small containers dry out fast in sun and wind. Stick your finger 1-2 inches into the soil; if it's dry, water until it drains freely from the bottom. Self-watering boxes with a reservoir can cut watering frequency to every 2-3 days.
What are the best plants for a sunny window box?
For full sun (6+ hours), petunias, calibrachoa, geraniums, lantana, and vinca thrive. For heat and drought tolerance, try portulaca or zinnias. If you want edibles, basil, cherry tomatoes (compact varieties), and nasturtiums all do well in a sunny window box.
Do I need drainage holes in a window box?
Yes - drainage holes are non-negotiable. Waterlogged roots rot within days. If your decorative box doesn't have holes, drill at least 3-4 holes along the bottom (1/2-inch diameter) before filling with soil.

How to Budget a Window Box Garden

A window box garden is one of the most rewarding small-space gardening projects you can do - fresh herbs outside the kitchen window, trailing flowers along a balcony railing, or a pop of color on a city stoop. The key is knowing your total cost before you head to the garden center, because the box itself is rarely the biggest line item.

Breaking Down the Costs

  • The box itself - Basic plastic boxes start around $10-$15, cedar or composite boxes run $25-$60, and decorative metal or self-watering planters can reach $80-$150.
  • Mounting brackets - If you're attaching the box to a wall or railing, budget $10-$25 for a sturdy bracket set rated for wet soil weight (a filled 24-inch box can weigh 30+ lbs).
  • Potting mix - Never use garden soil in a window box - it compacts and drains poorly. A quality lightweight potting mix runs $8-$18 for a bag that fills one to two standard boxes.
  • Plants or seedlings - A 4-pack of annuals typically costs $4-$8; individual 4-inch pots run $3-$6 each. A nicely filled 24-inch box usually takes 5-7 plants.
  • Slow-release fertilizer - Window boxes deplete nutrients fast due to frequent watering. A bag of slow-release granules ($6-$12) mixed in at planting feeds plants for 3-6 months.

Weight and Bracket Safety

Wet potting mix weighs roughly 50-60 lbs per cubic foot. A 30-inch box filled 6 inches deep holds about 0.9 cubic feet - roughly 45-55 lbs fully saturated. Use brackets rated for at least twice the expected weight and anchor into studs or masonry, not just siding.