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Ask a Master Gardener: Let There Be Light

By Barbara Boone, Mobile County Master Gardener www.mobilecountymastergardeners.org


. . . or at least enough light to get vegetable and flower seedlings off to a good start even though temperatures could still be too low to plant outside. While others are still working on putting up or taking down holiday lights at year’s end, many gardeners are working on their grow light systems, getting them in working order, ready to start seeds for the upcoming growing season.

Commercial seedling growing is usually done in greenhouses where lighting and temperature are closely monitored. However, most home gardeners don’t have the luxury of a greenhouse in their backyard. What we do have is the ability to plant seeds under lights in a space large enough to accommodate a single- or multi-shelf setup and an electrical outlet.

So why are grow lights more beneficial to start seedlings?

· Healthier seedlings with strong, compact stems.

· Better survival rate with less reseeding necessary.

· Less waste with fewer seeds needed and less dirt required.

· Much wider choice of varieties from seeds rather than purchased transplants.

There are many light systems in the marketplace, but there are two primary grow light systems for the home gardener to choose: fluorescent and LED (light emitting diode).

There are certain factors to consider before choosing a grow light system:

· The ultimate size of the plant to be placed under lights.

· The dimensions of the space designated for the light system.

· The type of plant to be placed under lights. Plants that will be leafy, flower, and produce fruit are good choices to begin under grow lights.

After choosing a light system, it is important to understand the measurement of brightness. Most home gardeners will choose a light system based on watts and lumens. Wattage is the amount of energy the system is using. Lumens let us know how much light the light source should produce and how much light produced vs heat production. A light source may be perceived as perfect for growth, but we see light differently than plants, meaning that a high lumen number may seem correct, but that light may not be better for photosynthesis. Keep in mind light may produce unwanted heat which could even damage plants. (Note: Available light systems have calculations showing the required wattage in the product guide.)

Fluorescent systems:

Fluorescent lamps are popular with home gardeners due to a wider choice of diameters and lengths to accommodate the chosen system’s space requirements. The smaller the diameter of the light tubes, the greater the efficiency. Example: a T5 tube vs a T12 tube is more efficient and is readily available at gardening centers. Fluorescent lighting works well for leafy vegetables like lettuces, spinach, and herbs.

LED systems:

LED systems are gaining traction today because even though LEDs are more expensive to purchase initially, they have been shown to outperform fluorescent light systems in operating cost, maintenance, and plant health. A grower can manipulate light vs dark during the shorter and darker days of winter. LEDs have the advantage of lasting longer and do not emit a lot of heat, making it easier to control the growing environment because less heat means less transpiration (movement of water throughout the plant) which cuts down on watering.


The closer the LED source is to the plant the better, but keep in mind that monitoring light distance to plant is still required so that the plant is not burned. LED systems have evolved to the extent that dual-band light color LEDs can be used for different stages of the plant’s growth. For example, blue light can be used for vegetative growth while red light can be used for the flowering stage.

Plants that do well under an LED light also include tomato, peppers, lettuces, spinach, herbs, and in addition, beets, turnips, collards, and broccoli. (Note: recommended distances are included in the system guide information provided with a LED light kit.)

Summary:

With prior research based on gardener needs, choosing a grow light system is a great way to supplement and extend growing seasons and yield despite the time of year or weather outdoors.

For more information, check out these university resources:

A variety of plants under LED lights by Miri Talabac, Univ of MD Extension

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