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M.W. van Iersel, P.A. Thomas, R.B. Beverly, J.G. Latimer, and H.A. Mills

Pre- and posttransplant growth of plug seedlings is affected by the nutrition of the plants. The effects of weekly applications of nutrient solution with different N (8-32 mm) or P and K (0.25-1.0 mm) levels on the growth and nutrient composition of impatiens (Impatiens wallerana Hook. f.) and petunia (Petunia ×hybrida hort. Vilm.-Andr.) plug seedlings were quantified. Impatiens and petunia pretransplant seedling growth was most rapid with a \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{1}\) \end{document} concentration of 24 or 32 mm (N at 336 and 448 mg·L-1), while P and K had little effect. Increasing the N concentration in the fertilizer also increased shoot tissue N levels of both impatiens and petunia and decreased shoot P level of impatiens and K level of petunia. Posttransplant growth was most rapid in plants that received N at 16 to 32 mm. Decreasing P and K from 1 to 0.25 mm in the pretransplant fertilizer reduced posttransplant growth. Shoot P level of impatiens 15 d after transplanting decreased from 6.9 to 4.8 mg·g-1 as the pretransplant fertilizer N concentration increased from 8 to 32 mm, while N level increased from 18 to 28 mg·g-1 as P and K fertilizer concentrations increased from 0.25 to 1 mm. Using posttransplant growth as a quantitative norm for plug quality, the sufficiency ranges for tissue N level are 28 to 40 mg·g-1 for impatiens and 30 to 43 mg·g-1 for petunia plugs. These results indicate that fertilization programs for high-quality plug production should focus on N nutrition, and that plugs can be grown with greatly reduced levels of P and K.

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M.J. Lareau and M. Lamarre

Plug or bare root strawberry plants were planted on raised beds with black plastic mulch from mid-June to early-August. The early plantings gave the most developped and productive plants but these required several derunnerings to avoid overcrowding. Due to the unavailability of runners, it was not possible to establish plug plants before mid-July. Field losses of dormant bare root plants were high for the July planting. The use of a perforated polyethylene rowcover from October to May increased yield and fruit size.

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A. J. Turgeon and J. R. Street


Rate of coverage from plugs of ‘A-20’ Kentucky bluegrass (Poa pratensis L.) planted in Flanagan silt loam and treated with oxadiazon at 3.4 kg/ha increased as mowing height increased from 1.9 to 3.8 to 7.5 cm and with fertilization at 25 kg N/ha per growing month or higher. Sod strength measurements taken 2 years after planting were highest in plots receiving 25 kg N/ha per growing month compared to 0, 50, and 100 kg. Where plugs of 48 cultivars of Kentucky bluegrss received the same oxadiazon treatment, phytotoxicity ranged from no injury to complete necrosis.

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Holly L. Scoggins, Douglas A. Bailey, and Paul V. Nelson

Substrate electrical conductivity (EC), pH, and nutrient content should be monitored frequently during seedling plug production. Current testing methods are either complicated, unsuited to plug production, or interpretation standards do not exist. This study compares the press extraction (PE) method developed at North Carolina State Univ. with the saturated media extract (SME) method and the 1 substrate: 2 water suspension method (1:2). These solution extraction methods were applied to plug trays containing peat-based germination mix treated with four levels of fertilizer. Two sample sizes of 20 or 60 plug cells were used to determine if the smaller, less destructive sample size would produce satisfactory results. Resulting pH values varied within 0.3 units among methods, but variability in EC and nutrient content was greater. The PE method resulted in the highest values for EC, NH4 +-N, NO3 --N, K, Ca, and Mg while sample size had little effect on analyses. The three extraction methods were then compared on peat- and coir-based substrates. Within substrates, pH, EC, and nutrients tested were similar for the PE and the SME. The coir extract had a higher pH and much higher levels of K and Na than did the peat extract but was lower in N, P, Ca, and Mg. Overall, fairly strong correlations among testing methods were found, especially between the SME and PE.

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Kay Oakley, Robert Geneve, Sharon Kester, and Myra Stafford

Root and shoot development in Marigold `Little Devil Flame' was studied after being grown for varying lengths of time in 392-count plugs before transplanting to six-pack cells. Seedlings were grown for 0, 5, 10, 15, 20, and 25 days before transplanting to six-packs. All plants were measured at day 25. There was no significant difference in total root length, area and dry weight per plant or in leaf area and shoot dry weight per plant for seedlings transplanted from 0 to 15 days. Both total root dry weight and total shoot dry weight of seedlings transplanted on day 20 was reduced by 32% compared to seedlings that were not transplanted. Total root dry weight of seedlings transplanted at day 25 was reduced by 60% while total shoot dry weight of seedlings was reduced by 56% from those not transplanted. In a separate experiment, the growth rate of seedlings grown in plugs was sigmoidal (r 2 = 0.98). Growth rate was significantly reduced between 20 and 25 days in the plug. These results suggest that root restriction in the plug may be a factor in the reduction of seedling growth following transplanting.

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Chin-Chang Chu and Kenneth W. Mudge

Rockwool plugs were placed in Magenta G-7 boxes (Sigma) and then autoclaved at 121°C for 20 min. Fifty milliliters of cool autoclaved liquid medium was poured into Magenta G-7 boxes in aseptic conditions before microcuttings of Amelanchier, Cercis canadensis, cherry, and apple were transferred. Murashige and Skoog medium (MS, M-5519, Sigma) containing 30 g·L–1 sucrose, and with/out 1 ppm of NAA, pH 5.5 were used in all experiments. All cultures were incubated at 23 ± 1°C under a 16-hour lighting period with a light intensity of about 4000 lux of white fluorescent light. Microcuttings of Amelanchier, Cercis, Apple, and cherry rooted in rockwool plugs in 3 weeks after transfer and were ready to be out-planted in 6 weeks. Out-planted plantlets were leached with tap water and potted in 4-inch pots with Metrolite mix, then, placed in mist bench under 50% shade for 2 weeks before taking to bench with full sun light. The survival was 100%. Conditions and growth rate of rockwool-plug-rooted plantlets were much better than those plantlets rooted in agar medium. Rockwool plug plantlets had 2–3 flushes of growth before dormancy in greenhouse and were ready to be planted in the field or garden in 8 months after out-planting. Using a rockwool plug system simplifies out-planting procedure, produces better plantlets, increases out-planting survival, and greatly shorten time needed from out-planting to field-plantable size. This system is a very useful system for difficult-to-root woody ornamentals.

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Fumiomi Takeda Takeda, Stan Hokanson*, John Enns, Penelope Perkins-Veazie, and Harry Swartz

`Chandler' strawberry plants were propagated in tissue culture and grown from April to August in a protected environment to produce stolons. July-harvested daughter plants were stuck in cell packs with rooting media and placed under mist sprinklers, or cold stored at 2 °C for 42 days. Among the July transplants, some were kept in the greenhouse until field planting (14 Sept.) and others were moved into a cold room on 14 August. Daughter plant size and position on the stolon affected rooting and quality of transplants. July-harvested daughter plants that were plugged and misted after being cold stored for 42 days developed fewer roots than daughter plants plugged immediately after detaching from mother plants in July or August. In the field, transplants produced from daughter plants harvested in July and cold stored for 42 days developed more stolons than transplants from July- and August-harvested daughters that were not exposed to cold storage treatments. Larger daughter plants produced more branch crowns than did smaller daughter plants during the fall. All transplants from daughter plants harvested in July and propagated without cold treatment bloomed by November. Fruit production ranged from 521 to 703 g per plant. `Chandler' plants from daughter plants that weighed 10 g produced 10% greater yield than those that weighed <1.0 g. Plants generated from daughter plants plugged in July produced 26% more fruit than those plants plugged in August. Greenhouse soilless systems can be used to grow `Chandler' mother plants for generating runner tips and transplants for the annual plasticulture in colder climates. `Chandler' plants produced in July can yield a late fall crop under high tunnels and more fruit in the spring than August-plugged transplants

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Junne-Jih Chen, Yung-Wei Sun, and Tzay-Fa Sheen

Seedlings of tomato (Lycopersicon esculentum Mill.) and cabbage (Brassica oleracea L. var. Capitata) were planted in 240-cell plug trays in the greenhouse and subjected to irrigation with water at different temperatures once a day. Irrigation with cold (5 to 15 °C) water reduced stem length of tomato by 28% to 32% in comparison with irrigation with water at room temperature (27.5 to 30.5 °C). Use of water at 10 °C did not affect total shoot dry weight but increased the shoot dry weight per centimeter of stem. Irrigation with water at 5 °C reduced stem length of cabbage seedlings 40%, but use of water at 10 and 15 °C did not. Both shoot and root dry weights were increased by irrigation with water at 10 °C. These results demonstrate that irrigation with cold water provides an effective method for improving the quality of plug-grown seedlings.

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Erik S. Runkle and Royal D. Heins

Environments with a low red (R, 600 to 700 nm) to far-red (FR, 700 to 800 nm) ratio (e.g., with high plant density) promote stem elongation, and a high R: FR suppresses it. While FR light promotes stem extension, it is also required for rapid, uniform flowering of many long-day plants. We investigated how a new FR filter [creating a FR-deficient (FRd) environment] influenced plug growth and subsequent flowering of pansy (Viola ×wittrockiana `Crystal Bowl Yellow'), petunia (Petunia ×hybrida `Carpet Pink'), impatiens (Impatiens wallerana `Accent Rose'), snapdragon (Antirrhinum majus `Liberty Scarlet'), and tomato (Solanum lycopersicon `Beefmaster'). One-week-old seedlings were placed under three filter treatments with 16-h photoperiods: the FRd filter, a neutral-density filter (N) that transmitted a similar PPF, and transferring plugs from the N to the FRd filter when leaves of each species began to touch (7 to 11 days later). The predicted phytochrome photoequilibria under the FRd and N filters was 0.80 and 0.72, respectively. After 25 to 35 days at 20 °C, node number and stem (or petiole for pansy) length were collected. Twenty plants of each species and filter treatment were then transferred to 4-inch pots and grown under natural photoperiods (14 to 15 h) at 20 °C until flowering. Compared to plants continually under the N filter, stem length under the FRd filter was significantly reduced in impatiens (by 11%), pansy (by 18%), petunia (by 34%), snapdragon (by 5%), and tomato (by 24%). Flowering of plants from plugs under the FRd filter was delayed by 2 to 3 days for snapdragon, petunia, and pansy. Filter treatment of plugs had no significant effect on flower number or plant height at flower.

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M.W. van Iersel, R.B. Beverly, P.A. Thomas, J.G. Latimer, and H.A. Mills

Good fertilizer management is important in plug seedling production of bedding plants to prevent nutrient deficiencies and toxicities. We determined the effect of N, P, and K nutrition on the growth of plugs of impatiens (Impatiens wallerana Hook. f.), petunia (Petunia ×hybrida Hort. Vilm.-Andr.), salvia (Salvia splendens F. Sellow ex Roem.& Schult.), and vinca (Catharanthus roseus L.). For all four species, shoot N concentration was correlated linearly with shoot dry mass of the seedlings at transplant. Phosphorus or K concentration in the nutrient solution or shoot tissue had little or no effect on the shoot growth of seedlings, but shoot P levels increased with P concentrations in the fertilizer solution (luxury consumption). Salvia was the only species that also exhibited luxury consumption of K. Results of this study indicate that seedling growth of these species is mainly determined by N and this should probably be the main focus of fertility programs in the plug industry, while P and K applications can be reduced.