Designing Windowboxes

Choose a windowbox, or create one, and have it installed.
If you have a 2-story home, and windows for windowboxes, arrange to have it installed. You don't want to be the one climbing the ladder and possibly meeting a cartoon ending.

Make sure your window box has drainage holes. For drainage, place 2 inches of non-biodegradable packing peanuts or old wine corks in the bottom of the box, and then cover with landscape fabric to prevent soil from seeping out. I like to use those horrific styrofoam peanuts at the bottom of anything just to get rid of them, but they do work to elevate the plants and drain the box. They are also lightweight.

Fill the box halfway with potting soil, and add your plants. Add more soil to set them in firmly, and tamp down to eliminate air spaces in the box, paying attention to all the edges of the box. Gaps mean less soil for the plants, and runoff of water and fertilizer.

Make sure your plants are placed a few inches apart to give them room to fill out.
If you want instantaneous gratification, you can plant a lot closer. If you do this, you will need to pinch, divide or prune your plants to prevent overcrowding.

As with all container plantings, choose plants with similar water and light needs, and water them more often than plants in the ground. Water thoroughly once the soil has dried out. I use a re-cycled rubber mulch layer on top of the soil to keep the soil cool and retain water in those full-sun windowboxes. Any mulch, including gravel, will achieve this, but i don't like doing things more than once, if i don't have to. I don't call myself The Lazy Gardening Lady for nothing. The rubber mulch will not degrade, add much weight to the box, attract bugs, or leach anything into the box that might harm plants. Fertilize with an organic fertilizer every few weeks in spring and summer. I use a sprinkling of epsom salts at the time of planting, then regular liquid fertilizing with diluted fish emulsion. Plants growing in small spaces, with less soil and nutrients, need more food and water to perform.

Plants for Your Window Box

The popular windowbox gardening memes dictate these plant categories:

Thrillers

Are the focus plants, and dictate the rest of the design. These are the larger plant or plants in the back that are the focal point.

Spillers

Vines or trailing plants that spill over the edges and hang down from the windowbox planting. My favorites are english ivy, creeping jenny, and sweet potato vine.

Fillers

The main plants that bridge the space between the tall thrillers and the low spillers.

The Plan Behind The Plan

Repetition

Plant in groups of plants - like ivy, to create a flow between and around plants. Lots of vines can trail from the fronts and edges, and from under your main planting.

Focal Point

Choosing the centerpiece first, means the rest of your plant choices will fall into place. A dwarf ball topiary or dwarf evergreen ornamental looks pretty in the center of your planting.

Texture

Taller and flowing dwarf ornamental grasses make a great focal point in the center of a box. Other flowering plants will be packed in around your focal point.

Below are photos of some pretty ideas for planting your box.

Feel free to substitute any plants you like of the same height as the examples to create your personal design. Mix annuals and perennials, or just one or the other. Personally, i prefer a perennial selection that will return every spring. Vines are my "frame".

Your windowbox may be themed to contain florals, or create a decorative Edibles Windowbox theme of herbs or low-growing veggies in different shapes and sizes, with interesting foliage and flowers, and include vines. Naturally, you'll want to plant something that doesn't make the box naked after you've picked.

Choose decorative edibles like herbs and greens that will get a good pinch frequently for culinary purposes, but do not require removal of the entire plant. Or use plants that grow all season, and are harvested in fall, so that you have an entire season of display. Perennial herb windowboxes will come back to life in the spring, and don't have to be replanted, unless they outgrow the box. Different spiller vines might be added, if you wish. Salad Bar Windowbox theme gardens are also great designs, following the methods outlined above. Just remember that herb and salad boxes will need way more diligence and care than a floral theme windowbox. I wouldn't grow berries or dwarf fruit in these, as birds will probably use the boxes as feeding stations. They can't resist.

My hacks.....

- Once the season is on a roll, if a plant is not thriving or filling in the windowbox, i use high quality silk plants and vines to take their places. Most of my windowbox designs end up with half real and half artificial plantings. I hate empty spaces.

The window boxes are filled with large groupings of quite realistic-looking silk (and weatherproof) plants and vines for a winter and holiday display that defies the weather and season. My posers have lasted 6 or more full seasons without fading. But you must choose high quality, realistic-looking artificials that are weatherproof. Mine can take rain and snow, and hot sun, without damage. It's worth the initial investment to have plants on hand, should your plantings begin to lose a member or two.

- I can fit 6 clay pots inside each windowbox, which is bolted securely to the house, so they can bear weight.... I'll plant 6 filler plants in the pots, then insert the pots, and cover with more soil to fill in. Vines are planted directly in the windowbox soil, as the "spiller".

My plants seem to last longer and not need as much water. The same thing can be done in large container plantings.