Jan 06

Grow Light Plan

March 1: How do your seedlings look when you harden them off before transplanting; tall and scrawny or short and stout? If you are like me then it is probably the former; but I am getting better. Successfully growing plants from seed indoors is a mixed bag because our focus is out of order. Sunlight, water, air and temperature; sunlight, water, air and temperature; SWAT, SWAT, SWAT. That summarizes everything a plant needs to survive.

Water is the gift of life. Protected within the seed coat are a tiny plant and enough food to support it long enough to develop leaves and generate its own food through the process of photosynthesis. But, you do not need a gallon of water to germinate a seed; just keep it constantly wet until it germinates.

Air provides the carbon dioxide needed for photosynthesis, and the soil oxygen for the roots and microorganisms. We pump out more than enough hot air to support the seedlings and all the other house plants.

Temperature is not specific. All seeds germinate within a temperature range of fifteen to twenty degrees, and seventy degrees Fahrenheit is common across all plants. So the thermostat doesn’t need to be adjusted. That just leaves sunlight as the determining factor. A co-incidence that it is the first letter in SWAT, I think not.

Photosynthesis is triggered by the energy of the sun. On a bright winter day sunlight reflecting off the snow it can be blinding, but it still isn’t strong enough to fuel the seedlings. We adjust by providing artificial light, and this is where we drop the ball; we do not use the best light bulb available.

Very simply,Wattsequals heat, the higher the wattage the hotter the bulb; Lumens equals candle power, one Lumen for every lit candle; Kelvin equals light intensity, the higher the Kelvin number the brighter the light.

Years ago, when our only choice was an incandescent bulb, the decision was easy. The maximum suggested wattage for the socket, usually 100, provided about 980 lumens. That is a lot of heat, hot enough the burn leaves; not good. Moving the bulb away from the plant reduced the amount of energy available for photosynthesis causing it to grow taller and thinner as it stretched toward the light.

The solution was the fluorescent bulb; more lumens with less wattage. A 23 Watt fluorescent bulb is about equal to a 100 Watt incandescent bulb and provides over 1,600 lumens. So the bulbs can be closer to the plants without burning them; but we can do better.

Information on energy saver bulb packaging includes a Kelvin number. Given the same Wattage, a light can appear yellowish, about 2,700 Kelvin; or bluish white, about 5,000 Kelvin. The energy of the sun on a cloudy day is 5,000 – 6,500 Kelvin.

That is the number one priority. If you are starting plants indoors, use the highest Kelvin rated bulb you can find and keep it on for at least twelve hours a day.

A few years ago, I designed a low cost simple to make grow light. Here is the plan and a tutorial.

Plants are living organisms capable of manufacturing their own food by combining the inorganic nutrients carbon, hydrogen and oxygen. Nutrients are elements; all of the elements required for healthy plant grow by magnitude of use are: carbon, hydrogen, oxygen, nitrogen, phosphorous, potassium, calcium, magnesium, sulphur, boron, chlorine, copper, iron, manganese, molybdenum and zinc. The process of absorbing energy from sunlight, converting and mixing it with nutrients from the water and air to chemical energy (photosynthesis), is optimized at ideal temperatures. An easy way to remember what a plant needs is the mnemonic SWAT (Sunlight, Water, Air and Temperature).

  • Energy from the sun stimulates photosynthesis, with plants utilizing the full light spectrum to support cell growth and flower development.
  • Water dissolves minerals in the soil and assists in the absorption of nutrients through the plant feeder roots in the process of osmosis.
  • Air containing carbon dioxide CO2 is absorbed through pores (stomates) on the undersides of leaves.
  • Temperature regulates the speed of seed germination, rate of cell division and plant growth. Each plant has an optimum growing temperature range.
  •  Nature for the most part satisfies plant needs outdoors. We choose the best planting location for maximum sunlight, wait for warm weather to transplant our seedlings, and provide water between rainstorms; but nature does the rest. Indoors we have to substitute for nature and provide for the plant. We can easily address three of the needs.

  • Water – Moisten the soil to soften the seed coat for germination and transmit nutrients.
  • Air – Indoor air contains sufficient carbon dioxide to support photosynthesis.
  • Temperature – 640F to 720F is within the seed germination and growth range for most plants.
  •  Sunlight’s color, intensity and duration are more difficult to simulate indoors. Grow lights are used as the substitute with incandescent, fluorescent and/or halogen bulbs the lighting source.Color – Sun radiates light across the entire color spectrum from ultra violet through infra red. Plants absorb these colors for different uses and in varying degrees, mostly the blues and reds. Blue light assists in stem and leaf growth, and red does the same for flower and fruit development. When growing seedlings for your outdoor garden, you want to develop strong stem and leaf growth. That requires light from the blue end of the spectrum. Cool white fluorescent bulbs produce that light.Intensity – Plants follow the light source, seeking maximum absorption. The closer the light is to the plant, the shorter/stronger it will be. That is why plants sitting on a window sill become tall and leggy. You want to maximize intensity by placing the light as close as possible without damaging the plant. Incandescent lights get very hot and can prevent germination by drying and overheating the soil, increase the air temperature beyond the plant growth range, or burn the leaves. Fluorescent lights are cooler to the touch and can be placed closer to the plants.Duration – The photo-period is the amount of light a plant receives during a 24 hour day. Plants are triggered to flower as the photo-period changes. The longer the lights are on the better, and try to be consistent with the on/off cycle. The grow light shown in the image was made for about $22.


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    1. Bastien says:

      No Green Thumb. Tropical plants like it warm and enjoy a fine mist with water at room temp. It sdunos like the bugs that attacked your last plant was because there was mold in your dirt and the dirt did not get a chance to dry out thoroughly. The next time you buy a plant make sure you have the directions for care. Follow them to the T and you should be OK. Most need water once a week. Water them till it runs out the bottom then stop. As for food do not get on leaves just poor on dirt. Try again you’ll get it down sooner or later. Good Luck!!

    2. Peter says:

      I forwarded your request.

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