protection included Acjuilegia 

 chrysantha. Geranium endressii, and 

 Lobelia cardinalis. Only 10% oi Ascl- 

 epias tuberosa (1997 and 1998) and 

 25% of Dtcentra eximia (1997) sur- 

 vived without protection. 60% of 

 Phlox paniculata survived without 

 protection in 1997-98, but all unpro- 

 tected Phlox died in the cooler tem- 

 peratures of 1998-99. 



Table 2 summarizes the vigor of 

 plants grown under the different cov- 

 erings. Survival was generally lower in 

 1998-99 than 1997-98, particularly 

 for Asclepias tuberosa. Lower survival 

 may have resulted from cooler tem- 

 peratures and a later planting date in 

 1998, compared with 1997. All of 

 the coverings resulted in similar vigor 

 when averaged over the two years, 

 and results were considerably better 

 than under unprotected conditions. 



However, growth after being in 

 the heated greenhouse was different 

 than growth after being under the 

 other coverings. Plants grown in the 

 heated greenhouse during 1997-98 

 were very large and lush early in the 

 spring and peaked earlier than would 

 be useful for landscape sales. We 

 noted that these plants also tended to 

 be susceptible to crown rot during 

 spring regrowth. During 1998-99, it 

 appeared that plants from the heated 

 greenhouse had become very soft dur- 

 ing the winter and succumbed to dis- 

 ease during the winter or spring. 



Effect of Media on Plant 

 Survival: 



The amount of porosity is important 

 in container media because porosity 

 influences water and nutrient absorp- 

 tion and gas exchange by the root 

 system (Bilderback, 1982). Particle 

 shape, size, and distribution are con- 

 tributing factors of porosity. Roots, 

 swelling, cracking, or shrinking can 

 significantly alter the spacing of me- 

 dia particles (Marshall and Holmes, 

 1988). An ideal range for air porosity 

 of a container medium is 20-30 

 percent of the total container volume 

 (Bilderback, 1982). All media types 

 in this trial had an initial air porosity 

 over 20%, and air porosity decreased 

 to 11-15% during the winter. This 

 compaction may have been caused by 

 irrigation, freeze/thaw cycles, and me- 



Single foam 



■Covered 

 -Unprotected 



E 



:: ;. i=- a S 



Date 



Unheated greenhouse 



^Covered 

 — Unprotected 



O 



o 

 a. 



E 



Date 



dium decomposition. However, al- 

 though we tested media with a wide 

 range of peat/bark/perlite/vermiculite 

 ratios, there was no consistent effect 

 of media type on plant survival. 



Effect of Pot Size on Plant 

 Survival: 



Tall pots were used to see if im- 

 proved drainage was a factor in the 

 survival of overwintered herbaceous 

 perennials in containers. Because con- 

 tainers act as a perched water table, 

 as the height of the container (and 

 water column) increases, water reten- 

 tion decreases. Therefore tall contain- 

 ers effectively have increased drainage 

 compared with short containers 

 (Swanson, 1989). Roots of the surviv- 

 ing plants in our trial grew suffi- 

 ciently to fill the tall and standard 

 pots. However, container height did 

 not affect survival of plants in this 

 trial. 



So what did we learn from our two 

 years of experiments? 



• Protection of container perennials 

 using a synthetic cover was clearly es- 

 sential for plant survival, with almost 

 all plants dying if uncovered. 



• In the last two winters, which have 

 been fairly mild and without a lot of 

 snow cover, single foam, foam and 

 fleece, and an unheated greenhouse 

 with foam blanket all resulted in me- 

 dia temperatures about 30F warmer 

 than the minimum temperature in an 

 unprotected container. 



• Simple portable data loggers (cost- 

 ing around $80 each) provided useful 

 data that can help inform growers on 

 winter temperatures under different 

 environments. 



• Single foam, foam and fleece, an 

 unheated greenhouse with foam blan- 



20 



The Plantsman 



