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How to Prevent Rot With Window Boxes

By Annie Mulligan

Window boxes filled with cascading flowers can add beauty to your home. Wooden boxes are more attractive than the PVC and plastic counterparts. However, wood has an inherent flaw---it rots. There are several steps you can take to prevent rotting and ensure the long life and appeal of your window boxes.

Selecting and Preparing Window Boxes

Different types of wood products degrade faster than others. Pine for example, rots quickly, even when primed and painted or stained. Cedar and redwood have a longer life span, especially if several coats of stain or varnish are applied before planting. Pressure treated lumber is the best choice, though perhaps not as aesthetically pleasing, because the wood has been chemically treated to prevent degradation. If using pressure treated wood, seal with stain so the chemicals don't adversely affect your plants.

Prep your boxes with stain rather than paint. Stain penetrates and protects the wood better than stain. There are solid color stains available if you want the look of paint, as well as darker stains if you want a wood look. Apply at least two coats of stain, following the manufacturer's recommendations for drying times. If you want a natural look, apply at least two coats of varnish, again following the recommendations for drying times.

Drill several weep holes in the bottom of your window box. This allows adequate drainage for the plants, but more importantly, prevents a buildup of moisture that can adversely affect the wood.

Line the boxes, if possible, with plastic or galvanized containers to add another layer of protection against rotting. Drill weep holes into the bottom of these as well.

Add a layer of small crushed stone on the bottom of the liner, or on the bottom of the box if you're not using a liner, before planting. Stones allow water to drain away more efficiently. You can find crushed stones at many nursery locations. If that's not convenient, try a pet store that carries various size stones for aquariums. Look for stones about the size of a pea or a bit larger.


Things You Will Need

  • Drill
  • Varnish
  • Paint Brushes
  • Bag of crushed stone


  • Properly store your containers at the end of the season. Remove all the dirt and debris and keep them in a shed or indoors so that they're not exposed to the winter elements. This will help increase the life span of your boxes.


  • Never use pressure-treated window boxes if you're growing herbs or other plants that you will eat. Even if sealed, there is the possibility that the chemicals in the wood could leach to the plants. Several of these chemicals, including arsenic, are known carcinogens.

About the Author


Annie Mulligan is an editor, author, and developer of education materials for children in grades K-8 as well as for adult learners. She has published more than 100 books in reading, mathematics, test prep and language arts.