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Adam Dale and Theo J. Blom

The objectives of the study were to determine whether raspberries responded to decreased red to far-red ratio and whether it was more effective at the beginning or end of the dark period. Increased proportions of far-red light increased the internode length when at the beginning of the dark period on the three raspberry cultivars `Lauren',`Reveille', and `Titan'. Cultivars varied in that internode length also increased in ambient daylength compared to short days in `Lauren' and `Reveille', but not in `Titan'. They also responded differently to photoperiod: `Titan' and `Lauren' grew under short days, whereas `Reveille' ceased growth.

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Theo J. Blom and David Kerec

Potted bulbs of Lilium longiflorum Thunb. `Ace', `Nellie White', and `Snow White' were grown under either ambient photo period (APP), 8-h photo period using blackout (no twilight) between 1600 and 0800 HR (8PP) or 8PP extended with 1-h of low-intensity far-red radiation (9PP) at end-of-light period in a greenhouse with either a +5 °C DIF or a –5 °C DIF (= day – night temperature). In a second experiment, Easter lilies were also grown under APP, 8PP, and 9PP regimes with a constant day/night temperature (0 °C DIF) but with either a +5 °C or –5 °C temperature pulse for 3-h during end-of-light period. Each experiment was replicated twice and data was averaged over 2 years. The +5 °C DIF regime produced plants which were 19% taller than under –5 °C DIF. Plants grown under APP were 32% and 25% taller than under 8PP in the +5 °C and –5 °C DIF regimes, respectively. Regardless of the DIF regime, plant height under the 9PP was the same. In the second experiment, there was no significant difference in plant height of plants grown with the –5 °C compared with the +5 °C pulse at end-of-light period.

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Theo J. Blom and Wayne Brown

Four sterilants-bactericides (Physan-20, Fixed Copper, Phyton-27, and Virkon) were compared as preplanting dips of Zantedeschia elliottiana Engl. W. Wats `Yellow' (a susceptible cultivar) rhizomes to reduce plant losses due to latent field-infected Erwinia carotovora soft rot during greenhouse forcing as a flowering potted plant. All sterilant solutions were prepared in combination with Promalin, a commercially available product containing gibberellic acid (GA) used to enhance flowering. An additional group of rhizomes was inoculated with E. carotovora sp. as a preplanting dip in combination with the GA treatment but were not treated with a bactericide. Rhizomes were wounded by making two cuts on the distal part of the rhizome or left unwounded before application of the preplant dip treatments. After potting, plants were fertilized with either a high (3.0 mmol·L-1) or a low (1.0 mmol·L-1) calcium nutrient solution through subirrigation. More than 90% of the inoculated rhizomes collapsed within 5 weeks after potting due to bacterial soft rot. With the uninoculated rhizomes, the copper-based compounds (Fixed Copper or Phyton-27) provided better control of bacterial soft rot than either Physan-20 or Virkon only during the first 6 weeks of forcing. During the remainder of the forcing period, there were no differences in weekly losses of rhizomes with the four sterilants. Confirmation of Erwinia carotovora subsp. carotovora (Jones) Bergey et al. as the causal organism was made throughout the experiment. Incisions on the rhizome before planting or calcium nutrition during forcing did not have any significant effect on disease severity. Rhizomes treated with solutions of the copper-based compounds produced 0.5 flowers less per rhizome than either Physan-20 or Virkon. High calcium fertilization resulted in an increase of 0.5 flowers per plant compared to low calcium nutrition.

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Theo J. Blom and Brian D. Piott

Four freesia cultivars were exposed to 24 hour·day-1 high-pressure sodium (HPS) lighting during various stages of their development. Upon emergence, freesia plants were exposed to the following four lighting treatments: 1) ambient; 2) ambient until shoot length was 5 to 8 cm followed by HPS lighting until flowering; 3) HPS lighting until shoot length was 5 to 8 cm followed by ambient lighting; and 4) continuous HPS lighting. Supplemental HPS lighting was provided at 37 μmol·m-2·s-1 at plant level in a glasshouse. Continuous lighting or lighting during flower development hastened flowering but reduced the number of flowering stems per corm, as well as stem length and weight. Lighting during the vegetative and flower initiation periods produced minor effects. The main benefit of supplemental lighting was found in total corm weight.

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Theo J. Blom and Brian D. Piott

Low volume drip (2 l/h) was compared with 2 subirrigation ('trough' and `ebb and flo') systems for production of poinsettias and chrysanthemums in 15 cm diameter (1.6 l) `azalea' pots. Irrigation frequency as well as fertilizer rates were the same for all systems. The drip system received 280 ml per watering.

Two plantings of poinsettias (fall) as well as two plantings of chrysanthemums (spring and summer) showed no differences in plant growth between the drip and the subirrigation systems. Water uptake by the medium was similar for all irrigation systems, but water and fertilizer application was 70% higher for the drip system. Nutrients, measured at 4 depths within the pot at monthly intervals, increased with time and was markedly more concentrated in the top layer, regardless of the irrigation system.

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Theo J. Blom and Brian D. Piott

The Al content was determined in roots, buds, and stems of dormant florists' hydrangeas [Hydrangea macrophylla subsp. macrophylla var. macrophylla (Thunb.) `Mathilda Gutges' and `Brestenburg'] that were or were not treated in the field with aluminum sulfate. During the greenhouse forcing stage, previously nontreated plants were subjected to four successive weekly subirrigated applications of aluminum sulfate totalling 4, 8, 12, or 16 g/pot. Applications were early (weeks 2, 3, 4, 5) or late (weeks 6, 7, 8, 9), using the start of forcing as week = 0. The Al contents in stems and buds of dormant plants were about five to six times higher in field-treated than in nontreated plants. Roots were the primary location of Al accumulation (≈70%). Aluminum sulfate applications of 12 to 16 g/pot during greenhouse forcing provided commercially acceptable blue plants. Maximum foliar Al concentration was 50% higher in early than in late-treated plants and calculated to occur with 14.5 and 12.2 g aluminum sulfate/pot for early and late-treated plants, respectively. There was a positive correlation (r = 0.74) between blueness ranking and the Al foliar concentration of the two uppermost expanded leaves taken from flowering plants.

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Theo J. Blom and Richard B. Smith

Summer-grown Hydrangea macrophylla subsp. macrophylla var. macrophylla (Thunb.) were exposed for 1 week to CzH4 at 0,0.5,2.0,5.0,50, or 500 μl·liter-1 in dark storage at 16C for defoliation before cold storage. The number of leaves remaining per shoot for all cultivars decreased with C2H4 concentration, and >5 μl C2H4/liter was effective in defoliating `Kasteln', `Mathilda Gutges', and `Todi' but not `Merritt's Supreme'.

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Theo J. Blom and Brian D. Piott

The effect of constant 16C and noncontrolled soil temperature on flowering of four Alstroemeria cultivars grown in a greenhouse was studied over 3 years. Soil temperature regime did not influence either the start or cessation of flowering. During spring/summer, production was 15% lower under constant soil temperature, irrespective of cultivar. During fall/winter, the effect of constant soil temperature was cultivar-dependent; yield of `Red Sunset' was increased by 150%, while that for `Rio' decreased by 2270 relative to the noncontrolled. Annual production was not affected, but the ratio between the production of spring/summer and fail/winter decreased from 3.1 to 2.2 for noncontrolled and constant soil temperature, respectively.

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Theo J. Blom and Brian D. Piott

High-volume top irrigation (Chapin) was compared to subirrigation (ebb and flow) using 15-cm-diameter (1.56 liter) pot-grown chrysanthemums [Dendranthema ×grandiflorum (Ramat.) Kitamura] with peatwool (50 peatmoss: 50 granulated rockwool) as the growing substrate. Preplant moisture contents (25%, 125%, and 250%, gravimetric) and compaction (0, 20, and 50 g·cm-2) of the peatwool were also studied. Shrinkage of growing substrate was large (>309'6 of pot volume) when peatwool in the pots was not compacted. Compaction reduced shrinkage and produced plants with larger leaves, more fresh weight, and longer stems than without preplant compaction. Drainable pore space, container capacity, and total porosity was not affected by compaction. The higher preplant moisture contents increased drainable pore space but had no effect on plant growth. Chapin-irrigated plants had significantly more fresh weight (+ 24%) at the pea-size bud stage than plants grown in the ebb-and-flow system. The difference in growth was similar at flowering but significant only at P = 0.08. Soluble salts concentration in the peatwool and foliar nutrient contents differed at flowering for the two irrigation systems.

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Janni Bjerregaard Lund, Theo J. Blom and Jesper Mazanti Aaslyng

Controlling plant height without the use of plant growth retardants is one of the goals in future production of potted plants. Light quality with a low red to far-red ratio (R:FR) increases plant height. In this trial, the effects of light quality [R:FR ratio of 0.4, 0.7, and 2.4 (R = 600–700 nm, FR = 700–800 nm)] at the end of day were investigated on potted chrysanthemums using growth chambers. After a 9-h photoperiod, the 30-min end-of-day lighting was provided by light-emitting diodes at low irradiance by maintaining either red = 1 μmol·m−2·s−1 (Rcon) or far-red = 1 μmol·m−2·s−1(FRcon). After 3 weeks of end-of-day lighting, plants given the lowest end-of-day ratios (R:FR of 0.4 or 0.7) were taller than control plants (R:FR = 2.4). For low ratios of R:FR (0.4), the actual intensities of R and FR did not affect plant height, whereas for higher ratios of R:FR (0.7 and 2.4), plant height was greater for FRcon than for Rcon. Leaf area of the lateral side shoots was lower for plants treated with an R:FR of 0.4 compared with those of controls. Dry weight, stem diameter, number of internodes, and number of lateral branches were unaffected by the end-of-day ratio.