About Our Potted Tulip Trials

Each year, we trial 18 to 25 cultivars of "new and emerging" tulip cultivars. These are chosen based on presumed acceptance by the U.S. market, and are limited to those with more than ca. 2 acres of production in Holland, and to varieties that are available to the wider trade.

In our trials, two components are evaluated. The first is the required number of cold weeks for the variety. This is done by scheduling dates of cooling and forcing to give a range of cold duration of ca. 13 to 23 weeks. Typically, plants are removed from the cooler for forcing in the greenhouse (approximately 63 F constant temperature) every two weeks from ca. January 1 to late April.

The second component evaluated is the use of a plant growth regulator (PGR) drench. Tulips typically need a PGR to maintain a compact form, and this is especially true as the cold duration increases beyond ca. 17 weeks. It is also very cultivar dependent. Classically, A-Rest was the PGR of choice for tulips (1970's-1980's). Some 10 to 15 years ago, paclobutrazol (Bonzi and its generics, Piccolo, etc.) became more widely used. In the last ca. 5 years flurprimidol (Topflor) has become available in the industry.

Therefore, we routinely conduct a drench of 1 or 2 mg/pot paclobutrazol (Bonzi or Piccolo) and 0.5 or 1 mg/pot Topflor. These are applied as 120 ml (4 oz) drenches per pot about 3 to 6 days after bringing into the greenhouse (later drenches for early season, and earlier drenches for later in the season).

For each cultivar, basic information on characteristics, cold week recommendations and PGR needs are given. Clicking on the "More images and information" link on each cultivar page will bring up a .pdf file for each cultivar with images per year of the effects of cold weeks and PGRs used.