Starting seeds indoors part 1: Artificial plant lighting

January 13, 2011 § 2 Comments

The first in a series of three posts discussing starting vegetable seed in winter indoors:

  • Starting seeds indoors part 1: Artificial plant lighting
  • Starting seeds indoors part 2: Setting up a simple set of lights
  • Starting seeds indoors part 3: Vegetable varieties to start early and how best to plant them

Plant lights are used by gardeners- both amateur and professional- to start certain varieties growing before outdoor conditions are warm/bright enough, and also to provide optimal light levels during fruiting (e.g. commercial tomato crops) to maximise yields.

Artificial plant lights used to supplement existing light levels in a polytunnel or greenhouse allow the grower to manipulate day length and light intensity.

Let me explain some fundamentals about artificial plant lighting:

Plant lights are very similar to domestic lighting but the spectrum and the intensity is tailored to meet the needs of plants.

Fluorescent lighting is used largely for its ‘cool’ spectrum outputs, operating in the blue end of the spectrum. These lights are used for seedlings and for plants like lettuce which prefer shorter days with less intense light. Fluorsecent plant lights can be strip light or compact fluorescent lights (CFL’s), the latter look like large domestic energy saving bulbs.

Bulbs which emit from the ‘warm’ part of the spectrum- reds and yellows- mimic summer daylight and induce flowering. Tomatoes and peppers are good examples of plants which need a lot of red and orange light to produce fruit. This light is often supplied by sodium-type bulbs (pretty much the same as streetlights), which emit higher intensity light than fluorescent light.

Cool weather crops bolt in response to a variety of stimuli including day length, light intensity, intensity of red and yellow light, air temperature and soil temperature.

We use plant lights at our nursery to start chillies and sweet peppers in December. These plants have compact growing habits and after reaching a certain height their growth then shifts to concentrate on bushing out and strengthening stems.

As the UK has a less than ideal growing climate for chillies and sweet peppers (and aubergines, tomatoes, sweet potatoes, figs, olives, etc, etc) these early sown plants have a head start on seed sown in spring. They are that bit bigger when planted in the ground (or potted on in readiness for good planting conditions) and tend to ‘pop’ into growth and rapid flowering. The harvest period is extended and therefore there is more to eat.

Pepper and aubergine seeds are notoriously poor germinators when soil is too cold, so controlling conditions extends to supplying bottom heat. This is an important point as you have to remember to recreate other environmental factors, not just the sun, when starting seed indoors- consider ventilation, soil/air temperature, drainage.

See also:

  • Starting seeds indoors part 2: Setting up a simple set of lights
  • Starting seeds indoors part 3: Vegetable varieties to start early and how best to plant them

PS If anyone out there has SAD grow seeds in winter! Its like St tropez in my polytunnel 🙂 I am gardening in sunglasses

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