Here are some general lighting thoughts to start the discussion on winter plant needs. To determine how much light a plant will require, consider where and how it grows best in its natural environment. Most vegetables, for instance, grow best in full sunlight, which means as much light as possible must be supplied to grow vegetables indoors. Foliage plants like the Philodendron grow in full shade and therefore can grow normally with relatively little artificial light. Exotic plants, such as Bromeliads, grow in varying conditions depending on the species. Some grow in deep shade in the jungle, while others grow in bright sunlight. The lighting level required for growth indoors depends upon the characteristics of the particular plant being grown.
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Bernie (Sunday, 04 January 2015 10:27)
Plants NEED Darkness
Plants need dark periods. Light (called photo-periods) and dark periods and their relative lengths have an effect on plant maturity. Recent studies have conclusively proven that it is not just the length of the day which affects growth, but the duration of the dark period which follows. The dark period of each day affects flowering and seeding of most plants. Although many plants can grow under continuous light, nearly all plants prefer a dark period each day for normal growth. All plants need some darkness to grow well or to trigger flowering. The ideal photoperiods of plants vary, some preferring long days and short nights; other the reverse; and some do best when the length of the night and day periods are equal
Tom Eckert (Wednesday, 07 January 2015)
To be a serious grower you have to take the time to learn what your individual plants need in the winter months to survive. One growing style will most likely not fit all requirements. Temperature, light and soil moisture needs can vary greatly between plant species. Many plants need a dry rest period in a dark location, others can continue to grow and bloom with the proper care.
Bernie (Monday, 12 January 2015 15:20)
A possible new answer to greenhouse lighting is from Theoreme Innovation, Inc. In competition with the newer compact fluorescent lights, (CFL’s) the LED lights are providing an alternative to using CFL’s. The LED (light emitting diodes) use no mercury in their operation. The CFL’s being a fluorescent lamp; still require a mercury pellet ever so small for their operation. The CFL’s are a great step in the right direction from the old fluorescent lamps which contain a large quantity of mercury. Remember seeing those black looking balls rolling around in fluorescent lamps? They are the mercury pellets that end up in landfills when the lamps are discarded or on your flooring when you break them in the house.
The TI-Smart Bar 1000 LED Grow Light is tested to be equivalent to a 1000 watt HPS system, but it uses 65 percent less electricity and heat than HPS lights. They are new on the commercial market, and possible available to the hobby grower in a few years. www.theoremeinnovation.com
Paul Alaback (Friday, 16 January 2015 00:18)
I have been thinking about this problem quite a bit as I starting my first winter growing season in a new passive solar sunroom/greenhouse. I don't have glass ceilings, just a series of skylights and large windows on south side, so light is an issue. Plants in windows grow great, but I wanted to expand the area in which I could grow plants in winter. I ended up buying two 300w LED lights which provide the correct light spectrum for leaf production or flowers or both. I suspended the lights about 20" above plants so it would cover most of my 4' x 10' raised bed. I found it very difficult to get appropriate info for how much supplemental light is needed. Most examples are for people using grow chambers. I ended up giving my plants about 4 extra hours of light a day, so they get a total of about 10 hours of light a day in the dead of winter. This made a huge difference in the growth of lettuce, kohlrabi, carrots and other veggies. It is still only about half of full sunlight but seems to work well for these plants. It seems like the longer day length was key to keeping the plants actively growing. I monitored light levels with dataloggers to figure out light regimes, but I am not sure you really need to go to this level of detail. I totally recommend LED lights. They use very little electricity, generate little heat, and give you the right light spectrum, so really seem like the way to go.
Tom Eckert (Thursday, 29 January 2015 13:30)
Paul, excellent information you have shared. The hobby grower is somewhat left to experiment with winter lighting in their individual greenhouses. Learning about individual plant requirements makes a big difference in winter growth. There are basically three types of light measurements used, "day neutral, short day , and long day, when talking about light requirements at any time of the year. Plant flowering is also dependent on light available to the plants and the length available. Growers use the light technique to force blooming and at times in conjunction with ambient temperatures the plants are subjected. I have been putting together a "how to grow it" type of information file for the plants I grow for my small spring business. Just cannot find a resource of complete information on the market.
Joe Malinak (Saturday, 12 December 2015 12:55)
I am looking at supplemental lighting for my Greenhouse. A 20x20. I was looking at Gavita and possibly Hydrofarm. Specifically looking at DE(Double Ended) lighting solution. Does anyone have any experience with these products?
Richard Schreiber (Monday, 14 December 2015 17:17)
Having recently upgraded my radiator type heating system in a Zone 4 Iowa greenhouse, we are doing great. I grow succulents and must maintain a 50+ degree Fahrenheit warmth during the 5 months of unseasonable outdoor weather. My leafy Euphorbias have dropped their leaves, while other plants that are winter growers are maintaining their leaves and doing well. Watering is kept to a minimum for both.
My wife's Meyer's Lemon tree has bright yellow fruit and we'll wait for our two granddaughters to harvest them for a Christmas adventure.
Tom Eckert (Tuesday, 29 December 2015 09:17)
Joe M : I looked on the web site and those double ended light do put out a very high light intensity. They do have some draw backs. They create a terrific amount of heat close to the lamp and very easily will burn your fingers. Also, always use cotton gloves or a cotton cloth when removing or installing a new lamp. The oils on a persons finger print will shorten its usable life due to the high surface temperature of the lamp boiling the oils on its surface of the lamp. Do not use close to water or water sprays as the lamps "will explode" when the cold water hits the hot surface. I would recommend looking at LED lighting.
Bernie (Wednesday, 06 January 2016 10:13)
Joe here is a LED supplier to check out.
A possible new answer to greenhouse lighting is from Theoreme Innovation, Inc. In competition with the newer compact fluorescent lights, (CFL’s) the LED lights are providing an alternative to using CFL’s. The LED (light emitting diodes) use no mercury in their operation. .
The TI-Smart Bar 1000 LED Grow Light is tested to be equivalent to a 1000 watt HPS system, but it uses 65 percent less electricity and heat than HPS lights. . www.theoremeinnovation.com
Joe Malinak (Wednesday, 13 January 2016 13:14)
Tom and Bernie. I appreciate you sharing information, very helpful. Moving from Melbourne, Florida where the majority of my Plumeria were planted in the ground, now living in Alabama I need to discovery best growing conditions for my area. I am looking for supplemental lighting within the greenhouse to get a jump start on Spring and awaken my PLUMERIA from their winter dormancy.( the shorten daylight and cooler temps drop the plants into dormancy). You also need to understand that my plants grange from 1 gallon to 45 gallon plants and all vary in size. Using T5's or LED's are somewhat impractical because of the shortened distance needed between light and plant. Based on input from some fellow Plumeria Growers I did go ahead with the PARsource DE 1000w Open Reflector. I have three for my Greenhouse and installed them earlier this week. I did use the gloves when installing the bulb, and yes they are hot, but not an issue at this time. I am hoping withing 2-3 weeks I see new growth. Will keep you posted, and again appreciate the information.
Paul Alaback (Wednesday, 01 February 2017 22:33)
Recently discovered a simple and fairly inexpensive way to measure light over entire 24 hr period that you can use to figure out if natural light plus artificial light is giving you enough light for your plants in your greenhouse. It is called a ScoutDLI meter (http://www.specmeters.com/lightmeters/dli100/). After leaving it on for 24 hrs it then tells you how many DLI or (daily light integral of the wavelengths used by plants) it measured. You can then look up how many DLI needed for different kinds of plants. DLI is the unit used for commercial greenhouses so there is lots of info if you can measure light this way. Nice table of how much light needed for many kinds of flowers and other ornamental plants (https://www.extension.purdue.edu/extmedia/ho/ho-238-w.pdf). Generally need about 4-6 for foliage plants, and 14-18 for bright sun plants like tomatoes, zinnias etc. Another thing to consider is light and temperature can be related. Another words when it is cool plants may be able to get away with less light. My succulents seem to do fine in windows where they get <10 dli in winter; but citrus needs supplement light, otherwise they lose leaves and look horrible. I give them about 15 dli in winter.
Jim Guinn (Sunday, 10 December 2017 09:03)
I am in the process of retrofitting my greenhouse for winter growing. It has been a real learning experience and a challenge. So, so far I haven't tried growing in my greenhouse over the winter. I do have a small indoor kitchen garden (36" x 18") where I grow lettuce, spinach and basil all winter. I was using T4's and a cheap strip of LED grow lights that I bought from Amazon, but I just recently bought a Happy Leaf Procyon Ultra 33" LED growing light. For those of you really in PAR Energy, it's PAR Energy is 560 umoles/square m-sec (150 mm below - @6") above the plant canopy. It is now the only light I am using for this kitchen garden and the plant quality and growth have greatly improved.
Tom Eckert (Sunday, 04 February 2018 13:32)
Winter 2017 has been brutal with temps here down to zero degrees. I keep the greenhouse at 50 degrees. I use four of those indoor/outdoor thermometers for keeping a check on temps around the greenhouse. I keep all plants at lease 18 inches away from the outside walls where it is always colder. Keep the plants on the dry side so they grow slowly. Keep the plants cleaned as dead leaves can be a disease and insect problem with warm days. Check plants especially for mealy bugs as they grow in almost any climate. I do spray for them in winter. Spent a little over $1,000.00 on heating in the greenhouse this year. But it is my hobby and I do sell some plants in the spring.
Jack Berkley (Wednesday, 12 December 2018 12:02)
Hi Im a new member with a 16 x 32 earth bermed insulated greenhouse with 32 feet of south facing double walled polycarbonate windows 6 ft 6 in high, with 2ft poly on roof.
I'm frustrated in my effort to purchase supplemental lighting for larger transplants AFTER seed starting. I have seed starting lighting system. I need supplemental light for the transplanted seedlings when they are a few inches high. I decided Id go with LED, but which LED? I'm thinking T8s, 5000 kelvin, CRI 81. Is this a reasonable choice for transplants?