Should a greenhouse, light shelf or growth chamber be used? [Desc]

In a spring season study, plants grown in a 16-hour photoperiod greenhouse were indistinguishable from those grown in a 16-hour growth chamber. In winter season study, plants grown on a 16-hour fluorescent light shelf were just as healthy as those grown in growth chambers or greenhouses under the same photoperiod, though the light shelf plants were slower to flower and shorter.

Part 1: Spring Season
Part 2: Winter Season

 

What pot size worked the best in this study? [Desc]

This set of images shows plants growing in one of 4 container types. One image shows empty containers labelled for your reference. For each container size, four watering treatments are shown. Note how the symptoms of poor watering practices decrease as container size gets taller in 4" pots.

 

What soil mix worked best in this study? [Desc]

For quick visual comparison, the first two images show single replicates grown in each soilless mix, both in drained trays and in trays kept full of solution. Images of entire treatment groups show each soilless mix unaugmented (bottom row of each image) and augmented with calcined clay at different rates as row labels indicate. Each of these groups is repeated for three different fertilizer regimes as labelled below tray.

Part 1: Summary
Part 2: ProMix PGX
Part 3: ProMix BX
Part 4: ProMix HP
Part 5: Redi-Earth
Part 6: Sunshine Mix LA4
Part 7: MetroMix 360
Part 8: Other Media

 

Can a soilless mix be augmented to improve growth? [Desc]

Calcined clay granules of two different particle sizes were used for augmentation (sold under the trade name Turface MVP and Profile Greens). Compare single replicates of unaugmented soilless mixes with the same mixes augmented 50% by volume with larger of the 2 products (Turface). The same augmentation appeared to improve growth in a Sunshine LA4 mix low in iron and in Metro Mix 360 mix turned hydrophobic from long storage (labelled "18" in close up).

 

What root media worked best to cleanly remove roots? [Desc]

Informally tested, roots grown in small calcined clay granules (labelled "26" in the first image) came out of the pots with fewer particles attached or embedded. Plants growing in these granules were very small early in production. After fertilization was increased, they were indistinguishable from plants grown in soilless mix by the end of the experiment (last images). One image shows plants in 72-cell tray growing in larger granules that need to be flooded to the surface when irrigated due to low capillarity.

 

Does soil need to be pressed down prior to planting? [Desc]

The lower tray in this image had been compressed prior to seeding. There is no difference between the two trays.

 

Do seeds need to be misted to germinate? [Desc]

After stratification in a cold room (kept dark), seeds can be germinated under clear plastic domes, usually shaded with cheesecloth or muslin. Cheescloth alone may suffice if misted to keep humid and cool. Plants germinate very well on elaborate misting benches or under homemade PVC-pipe systems (last image).

 

What did this study show about the benefit of draining trays following irrigation? [Desc]

Note purpling and stress-induced flowering of young plants kept in clear water. Chlorosis and dying off of young plants in tray center occur when kept in fertilizer solution. Mature plants drained following each irrigation with fertilizer solution look much healthier than those kept in fertilizer solution continuously.

 

What if water HAS to be left in the trays? [Desc]

Augmentation with calcined clay granules improved growth of plants left in water, as did use of a so-called "self-watering" capillary tray. Image of the tray shows how we constructed using sponges, trays and capillary matting. The bottom tray holds water, the top tray has been cut with a slot for wicking water through the sponge to the matting.

 

Did use of capillary matting for sub-irrigation improve growth? [Desc]

When used with 200 ppm N fertilizer, capillary matting irrigation produced plants superior to those kept in 200 ppm N solution continuously, but inferior to those sub-irrigated, then drained of the same solution. Algae and shore flies were evident on the matting.

 

Was fertilizer required? [Desc]

Note purpling and stress-induced flowering of young plants irrigated solely with clear water. Mature plants have fewer and thinner flower stems and have senesced earlier than plants given fertilizer.

 

What frequency of fertilizing worked best in this study? [Desc]

Clearly fertilizer is necessary but at the strength of fertilizer of this study, fertilizing at each irrigation was too much. Plants grown in fertilizer solution solely, even if drained following each irrigation, had some dead plants late in production, most likely due to accumulation of salts in soilless mix. Fertilizing every other irrigation is recommended.

What fertilizer strength worked best in this study? [Desc]

These images show plants in two soilless mixes grown in either 50 ppm N or 200 ppm N fertilizer (alternated with clear water irrigations and kept drained). 50 ppm N plants exhibited purpling assocoated with phosphorous deficiency.

Did use of slow-release fertilizer result in healthy plants? [Desc]

Two pots of young plants side by side show that slow release fertilizer incorporation (left plant) resulted in larger plants. When plants matured, higher rates of slow release resulted in plants that were greener and larger than plants fertilized with liquid fertilizer (bottom row in image). Slow release appeared to delay flowering of 27 day-old plants grown in high light season.

 

What light intensity worked best in this study? [Desc]

Plants under 200 µmol/m2/s were larger and appeared greener than those at 100 µmol/m2/s. Higher light intensities than 200 resulted in death of some seedlings. It should be noted that in both experiments, no barrier was placed between the lamps and the plants, so the death could have been caused by high temperatures emitted from the lamps.

 

Can high intensity discharge lights be used? [Desc]

We compared plants grown using a combination fluorescent and incandescent lighting with three other treatments using high-intensity discharge (HID) lamps as sole source of illumination: high pressure sodium at 180 µmol/m2/s; metal halide at 250 µmol/m2/s; and a mix of these two lamp types at both 125 and 200 µmol/m2/s. All produced satisfactory plants. The plants under HIDs appeared to have longer petioles and narrower leaves (data not taken).

 

What photoperiod (daylength) worked best in this study? [Desc]

Plants grown in 8-hour or 12-hour photoperiods did not flower until initiated with a long day. Plants grown under 16-hour photoperiod thrived whether grown in growth chamber, light shelf or greenhouse. Plants grown under 24-hour photoperiod grew faster and flowered earlier than 16-hour photoperiod, though leaves of some plants yellowed - most likely from episodes of water stress (see close up).

Part 1: Greenhouse
Part 2: Growth Chamber Study (2004)

 

Does growth under 24-hour light hasten production? [Desc]

Growing Arabidopsis under 24-hour light posed many challenges such as supplying adequate nutrition, determining light intensity and avoiding water stress. We lost plants on two occasions from water stress. Please read the details section of this question (click on the blue D) before trying this at home! But the rewards were faster production. Time until 50% of the plants were in flower using 24-hour light was 19 days. That compares to 26 days in a 16-hour growth chamber, or 18 days in summer greenhouse, 26 days in spring-season greenhouse, or 39 days in a winter greenhouse.

 

Does 24-hour illumination damage plants? [Desc]

Note purpling of seedlings in first image caused by continuous light exposure at 300 µmol/m2/s. All plants were affected. Image in middle of row is continuous exposure at 100 µmol/m2/s. None of the purpling is evident, but an a few seedlings died. Image on right shows yellowing leaf tips of mature plants exposed to continuous 300 µmol/m2/s, but not 100 µmol/m2/s. These plants were continuoulsy sub-irrigated with a fertilizer solution, suggesting the damage is not from water or nutrient stress.

 

Can plants be transferred from low light environment to high light? [Desc]

Some Arabidopsis can be grown in greenhouses in summer, so it is not necessarily a shade-requiring plant. However, older plants transferred from low light to high light (high-intensity MH and HPS lamps) showed purpling of lower leaves within 24 hours of exposure. Young plants did not show this reaction when high light source was sunlight.

 

Can early flowering during long, hot days be avoided? [Desc]

Summer greenhouse production of Arabidopsis often results in plants with purple leaves and wispy, unproductive flowering stems that form early in the life cycle. We were not able to eliminate early flowering under long days but the flower stems appeared stronger and more productive when grown in cool temperatures. Increasing fertilizer helped reduce the purpling leaves. The first four images below compare stems, siliques ansd leaves of plants grown in a greenhouse versus a modified air-conditioned bench in the greenhouse. The last two images of plants growing under continuous light in a grwoth chamber show that increasing fertilizer rate slowed flowering slightly, reduced purpling leaves and thickened flower stems.

Can a greenhouse table be modified with air-conditioning? [Desc]

We converted this 5'x12' greenhouse table into an air-conditioned environment that used sun for a light source and exhausted discharge heat out the greenhouse exhaust fan so the room would not get hotter. It cost about $470, not including the metal table and small supplies we had on hand such as extension cords, tape, and thermometers. It was easily capable of maintaining 18-22C throughout July when greenhouse temperatures were often 29C. It held about 20 trays. See our Materials and Methods for Modifying a greenhouse table and greenhouse light-shelf with portable air-conditioners for improved cooling for details. See lines labelled "A/C Bench" on the graphs below of temperature and relative humidity. The last four images below compare stems, siliques ansd leaves of plants grown in a greenhouse versus the modified air-conditioned bench in the same greenhouse.

 

Can a shelf unit be modified with air-conditioning? [Desc]

We converted this shelf unit--bought at a local home improvement store--into an air-conditioned environment that used sun and fluroescent lamps for a light source. The greenhouse exhaust fans purged the heat made from the a/c units so the room would not get hotter. It cost about $540, not including small supplies we had on hand such as extension cords, tape, and thermometers. It was easily capable of maintaining 23C throughout July when greenhouse temperatures were often 29C. It held about 22 trays. See our Materials and Methods for Modifying a greenhouse table and greenhouse light-shelf with portable air-conditioners for improved cooling for details. The images below show step-by-step construction of the shelves, the a/c units, the fluorescent fixtures, reflective insulation, plastic film ends and front covers. See lines labelled "A/C Shelf" on the graphs below of temperature and relative humidity.

 

Did any treatments reduce fungus gnat infestation? [Desc]

The first image shows skeletonization by fungus gnat of leaves that lay on soil surface. We trapped and counted fungus gnats larvae using potato wedges. Larvae were identified by their clear transparent bodies and black heads. They were distinguished from shore fly larvae which are light brown and slower moving. Beneficial nematodes gave significant control.

 

How much imidacloprid (Marathon 1G) need be applied? [Desc]

All rates of Marathon 1G above the recommended rate resulted in smaller plants and delayed flowering. Poor mixing, even at recommended rate, resulted in non-uniform plants. Some necrosis was evident on leaf edges even at recommended rate (see close up). Plants grown with recommended rate flowered earlier than control plants, though some variables were not controlled (last image).

 

Do any insecticides or fungicides burn foliage? [Desc]

We've applied many insecticides and fungicides to Arabidopsis without damage to the plants. For a list of them, see the "details" section by clicking on the blue D following this question. Phytoxicity from sprays appear on plants 24-48 hours after spraying. Symptoms often include leaf marginal edge burn such as seen on the photos below of Pipron fungicide damage. Spray damage is very similar to salts accumulation in soil. Soil analysis can eliminate that as possible cause, especially if record keeping indicates a spray was recently made.

I've run out of space in my facility - how can I optimize it? [Desc]

Light shelves with wet location-approved fluorescent fixtures, rolling benches for greenhouses (see roll bars and moving aisle), modified tiered bench, and a Koldwave unit for portable air-conditioning without window or duct venting.

 

What is my worst Arabidopsis nightmare? [Desc]

To our knowledge, these are the first images showing symptoms of Impatiens Necrotic Spot Virus (INSV) on Arabidopsis, spread by thrips and fatal to this species. Immunostrip test kits show 2-stripes with positive result.

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