A question for Dan Gill: I’m looking for the best way to plant tulips in a sunny window box. The problem is that our three window boxes are 24 inches long but only 5.5 inches deep. After a layer of drainage pebbles and a layer of soil, I am afraid I will only have about 4 inches of soil to cover the tulips, and I have read they should be planted 5 inches deep. Do you have any suggestions other than buying deeper pots? — Jeremy Delany
Answer: Now is the time for everyone to plant tulip bulbs that have been refrigerated for the last 6 to 8 weeks. Tulip bulbs may be planted in the ground or in containers. The rules for planting, though, are different in the two situations.
When planting in the ground, tulips bulbs are planted in holes about 5 inches deep spaced 3 to 5 inches apart. However, you’re planting in containers. Your window boxes are long, narrow containers that fit on or are fastened under your windowsill.
When planting tulips in containers, we plant the bulbs very shallowly and closer together. The bulbs are planted with the tips just showing at the soil surface. The spacing is about 1 inch apart. So, depth of planting in the window boxes is not the issue you thought it was.
Also I’d like to clear up a bit of misinformation about adding a layer of drainage material in containers. These layers of gravel, pot shards, etc., do not improve drainage in any way. Indeed, water will actually perch on top of the gravel. Water is attracted more powerfully by the finer texture of the potting soil than the coarser texture of the gravel, and does not flow evenly from the soil into the gravel. Some of it will tend to “sit” in the lower potting soil just above the gravel. This actually tends to interfere with the flow of water through the potting mix and out of the drainage holes.
So, instead of improving drainage, a layer of gravel works against that very thing. It’s better for the potting mix to fill the container to the bottom. That way, the water flows smoothly and evenly through the potting mix (which is specifically blended to be fast draining) and out of the drainage holes. This applies to all situations when plants are grown in containers. So, just fill the window boxes with potting mix.
Dan Gill is a horticulturist with the LSU AgCenter. Email questions to firstname.lastname@example.org or add them to the comment section below. Follow his stories at www.nola.com/homegarden, on Facebook and @nolahomegardenon Instagram.