High Tunnel versus Climate-controlled Greenhouse: Transplant Time and Production Environment Impact Growth and Morphology of Cold-tolerant Bedding Plants.

Commercial bedding plant production in northern latitudes often begins in late winter and continues through spring, when average outdoor temperatures require growers to actively heat their greenhouses (GHs). High tunnels (HTs) offer energy savings as they are passively heated and cooled structures that have a low initial cost. As a result, they have been used in northern latitudes to advance and extend the growing season and improve the quality of high-value horticultural crops. However, there is limited published information on growing bedding plants in HTs in northern latitudes. Our objectives were to quantify the effects of transplant date in an HT with or without a rowcover (RC) compared with a traditional heated GH on the growth and morphology of three cold-tolerant bedding plant species at two northern latitude locations, Purdue University (Purdue) and Cornell University (Cornell). Seedlings of snapdragon (Antirrhinum majus L. 'Liberty Classic Yellow'), dianthus (Dianthus chinensis L. 'Telstar Crimson'), and petunia (Petunia x hybrida Vilm.-Andr. 'Wave Pink') were transplanted on weeks 13, 14, and 15 in 2012 (Purdue) and 2013 (both locations) and moved to either a glass-glazed GH or an HT without (HT) or with a rowcover (HT+RC). Several quality measurements increased when plants were grown in the HT compared with those grown in the GH. Dianthus and petunia transplanted at Purdue during week 13 in the HT and HT+RC were 33% and 47% shorter and had 51% and 31% more visible buds, respectively, compared with those grown in the GH. Similarly, petunia transplanted at Cornell during week 13 in the HT and HT+RC were 45% and 43% shorter, respectively, than their GH counterparts. The shoot dry mass of dianthus and snapdragon at Purdue was significantly higher when grown in the HT compared with the GH, regardless of transplant week or the use of RC likely because of increased daily light integral (DLI) in the HT environment. There was about a 1-week delay from transplant to first open flower for week 13 dianthus (at Purdue) and petunia (at both locations) when finished in the HT or HT+RC vs. their GH counterparts. Such a delay would be acceptable to growers who want to reduce the use of chemical grow th regulators and heating costs. However, at both locations snapdragon transplanted on week 13 to the HT or HT+RC environments were delayed by 22 to 26 days compared with the GH. A delay of over 3 weeks could interfere with a grower's production schedule, possibly making this crop unsuitable for production in northern latitude HTs. [ABSTRACT FROM AUTHOR]