Dig no more: Just till 2 inches for tulip bulbs, study finds

"Ad Rem" tulips planted on top of tilled soil and covered with mulch. Both varieties used in the study continued to bloom well in the third spring after planting.

Just till and fill, and toil no more when planting tulip bulbs. A Cornell study shows that a much easier method of planting tulip bulbs is just as effective as digging the traditional 6 to 8 inch holes for each bulb.

Gardeners need only "top plant": Till (loosen the soil) about 2 inches deep, place the bulbs on top of the soil and then cover them with a 2 to 4 inch layer of mulch and water to achieve successful tulips that will thrive year after year. No strenuous digging needed.

"Top planting is a good way to go," says William B. Miller, professor of horticulture and director of Cornell’s Flower Bulb Research Program, whose research report is free online at http://blogs.cornell.edu/hort/2011/07/07/top-planting-tulips-cuts-labor/ .

Although "avid gardeners enjoy being outside and the labor involved in planting bulbs," Miller suggested that the easy top planting strategy may allow them to plant "more bulbs more often without sacrificing their long-term potential in the garden."

Top planting is an old, yet underused method. Miller’s three-year study of the process demonstrated that it definitely works. In 2008, he used this method to plant "Ad Rem" and "Negrita" tulip cultivars, which are known as good "perennializers," in plots testing four different depths of mulch. Bulbs that were covered with 2 to 4 inches of mulch yielded the most flowers in 2009, 2010 and 2011. Bulbs covered in 6 inches of mulch produced fewer flowers, while bulbs that were not covered in any mulch produced no flowers (save for one Negrita tulip in the first year). In the study, a slow-release fertilizer was used, which Miller recommends.

Miller suggested that too little mulching may make bulbs susceptible to "animals making off with them," while over-mulching reduces the number of blooms each bulb can produce.

While Miller only tested tulips, he said that he suspects that the method would work with any bulbs. Testing whether top planting is better than traditional tulip planting methods was beyond the scope of the project, Miller said, but he assured that top planting produces healthy, high-quality tulip blooms.

As for when to plant the tulips: Optimum planting in central New York is from mid/late September through early/mid November. Bulbs root readily as long as soil temperatures are in the range of 40-50 degrees Fahrenheit, said Miller.

If you don’t get bulbs planted "in time"? "Plant them even into December. Really, anytime until the ground freezes. In other words, late planting is better than not planting!" Miller concluded.

Michelle Spektor ’12 is a writer intern for the Cornell Chronicle.