Q: I’m planning to add some window boxes to my house this spring. Any suggestions on how to do this and which herbs will do well there?
A: Herbs and flowers spilling out of a window box can be a delight to view from both inside and outside the house. Actually, herbs can add fragrance, color, and graceful form to any container arrangement. If you include some culinary herbs in a window box placed near the kitchen door or outside an easily opened kitchen window, you have the added convenience of easy harvests at dinnertime. The possibilities are virtually limitless.
In choosing material for a window box or a ready-made box, look for a rot-resistant wood such as redwood, cedar, or cypress, or go for a rugged plastic container with adequate drainage holes to allow excess water to drain out. Take care that the box is sturdy enough to hold the weight not only of the potting mix and plants but also of the water the herbs will require.
Secure the box’s brackets firmly to the window frame so that the box can’t fall and injure people, pets, or plants. Place spacers between the house and the box to help keep the siding from mildewing.
Select a potting mix that contains both peat moss to retain water and vermiculite or perlite to promote drainage of excess water. A product that’s useful in hot or dry climates is polymer granules. Mixing a small handful into the potting mix will cut down on watering frequency because the granules absorb and store water, then release it as it’s needed by the plants. Use of polymers serves as insurance against the soil’s drying out completely but doesn’t eliminate the need for water or for checking soil moisture.
Choosing the plants is the fun part of window-box gardening. A wide variety of herbs are perfectly suited to window boxes as long as you match your plants to the box’s exposure: a sun-loving herb won’t thrive in a shady location, and vice versa. If you plan to replant the box each spring, you can choose a mix of bright annuals and perennials without regard for their winter hardiness.
Some of my favorite herbs for sunny window boxes are scented geraniums (pelargoniums), calendulas, chives, rosemary, thymes, basils, and sweet marjoram. For partly sunny spots, try nasturtiums, parsley, chamomile, and sweet violets. Shady places are good homes for mints, lemon balm, sweet woodruff, and Cuban oregano. These herbs can be interplanted with old flower-box favorites such as pansies and petunias for reliable color throughout the growing season.
Fill each window box partway with moistened potting mix and position your plants however you like, leaving room for growth (imagine their size and shape two months from now). Add more potting mix between the plants, covering the root balls and tamping it gently until the mix is within an inch or so of the top of the box. Then water the entire box to settle the soil around the roots.
When the plants become established and start growing and blooming, they will look carefree—but only if they’re cared for. Check the soil moisture every day; you may need to water daily, particularly if the box is in a sunny location. If rain has fallen or the weather has been cool and cloudy, the soil may well be moist enough; in this case, don’t water but check again tomorrow. Apply a half-strength liquid fertilizer every couple of weeks if the plants don’t seem to be growing as fast as they might.
Harvest the tips of salad herbs whenever they are big enough and pick off any dead leaves and faded flowers to keep the herbs looking their best.
If an individual plant in your window box isn’t growing as vigorously as its companions or is disease-prone, it’s an easy matter to yank it out and try something else. You can choose plants to match your house or suit your mood and change them on a whim.
Kathleen Halloran, former editor of The Herb Companion, is a freelance writer living in Las Vegas, Nevada.
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