Vegetative phase: Simulating the Perfect Summer Day
Creating the right environment is key to promoting vegetative growth – leaves and roots. The right environment will also produce a plant which is short and stocky. This is the ideal ‘shape‘ for indoor growing:
1. High intensity discharge (HID) Metal Halide (MH) lamps are ideal for fast growing plants. They deliver high intensity light (penetrates canopy) and a spectral distribution that is rich in the blue part of the light spectrum. Light emitting plasma grow lights are even more efficient and productive but remain relatively costly for the average home grower.
2. Vegetative growth for short day plants is powered by long days of 18 hours or more.
3. Most plant species enjoy moderate relative humidity (~60%) and temperatures around 25 °C (77 °F). Also keep the night temperature differential (tDiff) as small as possible. With HID lighting, this temperature and humidity will be difficult to achieve without a proper ventilation setup. If this is the case, you may find it easier using fluorescent lighting instead.
Bloom phase: Powering the Flower
1. Use high pressure sodium (HPS) lamps, rich in the yellow, orange and red parts of the lighting spectrum, to drive the flowering stage. Many growers retain a 50 / 50 mix of metal halide and high pressure sodium lamps or use dual arc lamps for a fuller spectrum and a little ultraviolet (UV) to promote the production of more essential oils. Other emerging technologies such as double-ended lamps offer higher performance over a longer period.
2. If you are growing in a regular, ventilated grow room, consider upping the air-exchange rate. Flowering plants tend to prefer a gradual lowering of relative humidity to around 40 – 45 percent. Also, carbon dioxide consumption is reaching its peak and is therefore often the weakest link.
3. Don’t get complacent with bugs or diseases such as powdery mildew! Savvy growers periodically release beneficial insects (harmless bugs that feed on the ones that do the damage!) into their garden regardless of whether a pest has been identified. Regularly check both sides of foliage on all your plants—especially those that sometimes get overlooked in the corner. Remember—as flowering commences in earnest your job is to simulate the autumn. Cooler days and nights will help to add colours and character to your crop so, if you have the ability, cool your grow room down to the low 20s (Celsius). Most growers harvest their crops too early. Try an additional week with markedly lower nutrient concentration or just pure water for an even cleaner taste.
Avoiding the Stretch!
Many growers complain that their plants ‘stretch’ soon after triggering flowering, making them gangly and difficult to light efficiently. You can reduce stretch in a number of ways including:
1. Low day / night temperature differential (tDiff). Keep lights-off temperatures within 6 °C (11 °F) of your lights-on temperatures by using a thermostatically controlled block heater. For example: If your daytime (lights-on) maximum temperature is 26 °C (79 °F), aim for a nighttime (lights-off) temperature of 20 °C (68 °F) or more.
2. Less frequent irrigations. Drier root zones (especially at night) can also help to rapidly stimulate fruiting and flowering.
© Andrew M Taylor