Greenhouse Canada

Features Business Research

January 28, 2008  By Dr. Theo J. Blom

The exercise provides students with some “hands-on” growing as well as some basic research experience.

Each year, some students in the undergraduate agriculture/horticulture degree program take a course in greenhouse management. In this third/fourth year course, they learn about the effects of environmental factors on plant growth and development. The students conduct a research project where they can study a particular problem related to greenhouse production.

I provide the students with a number of potential projects, which I have picked up during the year (often grower suggestions), but the students are free to choose the topic. The projects are not considered to be conclusive as time does not allow them to do an extensive project, and some treatments are compromised due to time and space limitations. And sometimes mistakes are made as well.


The exercise provides the students with some “hands-on” growing as well as some basic research experience, and hopefully the exposure to greenhouse production provides some incentives. Projects are usually done by two students working together. Below are short summaries of what the students accomplished during the winter semester of 2006.

20aRooting response of Mandevilla cuttings to IBA by either dipping or submersing

By Greg Boyd and Thomas Tregunno

Research was conducted to evaluate the use of liquid solutions of indole-3-butyric acid (IBA) at 0, 1,000, 4,000, and 10,000 ppm IBA, and two methods of application (basal dip and complete submersion) of Mandevilla cuttings of different ages along the vine. The results showed that cuttings of different age responded linearly to IBA concentration and only mature cuttings treated with 10,000 ppm IBA achieved a rooting percentage greater then 95 per cent (Figure 1). There was no evidence that submerging cuttings improved rooting over dipping cuttings, although roots were initiated higher up the stem.

Growth and nitrate accumulation in spinach and lettuce grown in nutrient film technique using either organic or inorganic fertilizers

By Dan K. Mackinnon and Luise Olbrecht

High nitrate levels in the tissue of leafy vegetables are of concern for human health. The objective of our study was to compare organic with conventional hydroponic production of lettuce and spinach in order to determine whether organic production would reduce the nitrate levels.

Six nutrient film technique (NFT) hydroponics systems were used to grow both spinach (Spinacia oleracea cv. ‘King of Denmark’) and lettuce (Lactuca sativa cv. ‘Simpson Elite’) using three different concentrations for both organic and conventional fertilizers. Individual macro-nutrient levels (N, P, K, Ca and Mg) were kept the same for each fertilizer treatment. 

Results were inconclusive as it became apparent that NFT was incompatible with the organic fertilizer at any concentration. The fertilizer appeared to be concentrating in the rockwool substrate, causing plant death within one week from placing young seedlings into the NFT system. As a consequence, nitrate concentration could not be determined in the tissue.

20bPaclobutrazol applied pre-emergence and post-emergence to control height of petunia x hybrida ‘Purple Wave’ in plug trays

By Allan Sutherland and Paul Vos

Pre-emergence media and post-emergence foliar applied sprays of paclobutrazol (Bonzi) were compared for height control of Petunia x hybrida ‘Purple Wave’ petunia plugs. Four pre-emergence media drenches were at 0.125, 0.625, 3.125, and 15.625 mL of Bonzi per L (0.5, 2.5, 12.5 and 62.5 ppm paclobutrazol) using a volume of 1L of solution per square metre. Foliar sprays were at the same concentrations as for pre-emergence at a volume of 0.2L per square metre.

Pre-emergence drenches were applied at seeding to the plug medium substrate. Post-emergence sprays were applied 31 days after seeding. Size of plants were evaluated 47 days after seeding. Germination in trays that received media drenches were significantly reduced (77 to 55 per cent) compared to the average of control and foliar applications (90 per cent). Plant height and length of leaves decreased linearly with an increasing concentration of paclobutrazol, regardless of method of application (Figure 2). Number of leaves per plant was not affected by growth regulator application. Plant size was reduced by 28 per cent and 32 per cent with a media drench of 0.5 ppm and a foliar spray of 12.5 ppm, respectively.

Effect of light intensity on growth characteristics of Ostreatus pleurotus and O. pulmonarius

By Eric Peterson

The effect of light intensity on growth characteristics of two oyster mushroom species, namely O. pleurotus and O. pulmonarius, was examined. Pre-colonized 10 kg bags of wheat straw of both species were kept under 60, 110 or 160 µmol m-2 sec-1. Fresh weight and large fruiting bodies (>25 g) of O. pleurotus decreased with increasing light intensity. No statistical effect of light intensity was found for O. pulmonarius.

Temperature and consequently relative humidity may have confounded the effect of light intensity due to experimental design. As O. pulmonarius is a darker species than O. pleurotus, it is possible that this darker predisposition could have lessened the relative energy demands for O. pulmonarius. Further studies should examine the relationship between mushroom pigmentation and the increased tolerance to higher light intensities.

20cEffect of water temperature and frequency of watering on the height of potted Easter lily (Lilium longiflorum)

By Jessica King and Christi Vandenbos

The water temperature for overhead irrigation is one of the most important non-chemical factors determining plant height of Easter lilies. In our experiment, the effects of water temperature (2, 6, 10, and 14˚C), as well as two overhead irrigation frequencies (twice/week or once every two weeks), were compared for height control.

The volume of overhead irrigation was 100 mL per irrigation, and all plants received the same amount of solution. The treatments started on Jan. 31 (plants were about 20 cm tall). Plant height at flowering increased linearly with water temperature at a similar rate for both frequencies (Figure 3), but the plants irrigated twice per week overhead were about four centimetres shorter than those watered biweekly. Plants irrigated with 2˚C water were slightly delayed.

The effects of soil pH on growth and development of gloxinias and cucumbers

By Charles Inthathira and Dave Pieterse

Soil pH may affect plant growth and development in reducing available nutrients to the plants at high pH and providing toxic levels at low pH. Gloxinias and cucumbers were grown in soil-less substrates adjusted to varying pH levels to determine its effects on growth and development. Initially, the lowest pH level tested was 3.5 and increased by one pH level up to a pH of 8.5. During the experiment (6-8 weeks), the higher substrate pH levels tended to decline to pH levels between 6.5 and 6, which likely was due to the fertilizer (20-8-20) used in the irrigation watering.

The cucumbers were grown from seed while the gloxinias were started as rooted cuttings before the start of the treatments. The optimal pH for cucumber growth was between 5 and 6, with a mean fresh weight of 17.7 g, compared to 10.2 g for seedlings grown below 5 or above 7.

Differences in growth were minimal for the gloxinias, but the chlorophyll content showed a slight decrease with increased pH, which resulted in gloxinias that were slightly darker at lower pH. The pH treatments of 3.5 and 4.5 had the lowest amount of growth, while plants grown in pH levels of 6.5 to 7 had adequate growth.

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