Speed up Flowering Outdoors

If you took my advice and started an outdoor garden early indoors or grow outdoors already or know someone who does, you may benefit if you read this.

I suggested in past posts ways to speed up the growth cycle vegetatively and  during flowering . Here is a neat trick I learned this summer to speed up flowering outdoors that maybe you can still use this summer or remember it for next. If you are growing plants that flower the end of summer i.e. in response to long nights (12 hours dark) you can speed up the flowering by placing something over the plants to fool them into thinking it is later in the season. The person I spoke with used a 5 gallon black bucket (which can be sent to your house from HTGSupply.com). You just put the bucket over the plant a couple hours before dark and take it off in the morning. Make sure first that the plant is not going to be bent and broken (you must do this when the plant is small). If the ground is uneven, make sure that you put dirt around the base so that light does not get in. Then a few hours after sun rise you take off the bucket. This will fool the plant into thinking it had a 12 hour night and it is much later in the grow season. This will speed up or start the flowering response. ONE WARNING: Do not let the direct sun hit the black bucket when it is on the plant, you will cook (kill) your plant in an hour or less. If your plants get early morning sun put the bucket on early in the evening and take it off at night and if they get late day sun, put the bucket on at night and leave it on longer in the morning.

How this works is due to the way that plants measure day length; they use a molecule called phytochrome. There are two types of phytochrome light and dark. Light (energy) from the sun or your grow light turns dark phytochrome into light phytochrome and without light, light phytochrome turns to dark. Plants that flower end of summer flower when the dark phytochrome is in a high amount. So, when you put the bucket on the plant it will have 12 hours of dark (make dark phytochrome) which will cause the plant to being to make hormones that signal it to flower. (One ‘night’ might be enough but you can do a couple more to really speed up the process)

Do this after the summer solstice the longest day of the year (around June 21 most years) and your plants will fully develop flowers sometimes weeks ahead of schedule. This works because as the days get shorter, more dark phytochrome accumulates. Normally it would take weeks to reach the critical amount of dark phytochrome but since your plants had a 12 hour (bucket) night, they have the critical amount of dark phytochrome and with the ever shortening days the dark phytochrome will stay in a high concentration and continue to signal the plant to flower. I say this because after the solstice the days get shorter so there will be less and less day light (light phytochrome).

This won’t work for light insensitive plants, or plants that will be very tall after the summer solstice, but you could use this before your plants get big and it should still speed up the flowering rate. You could also use this trick early in the summer (before the summer solstice) to see if plants have the flowering characteristics you want. You can cause your plant to flower, and then it will revert back to mostly vegetative growth until end of summer. Using a bucket to induce flowering in May or June may stress the plants and may reduce plant size, but can make sure you don’t grow any plants that have negative flowering characteristics. Anyway, I thought some of you might be able to use this trick to speed up flowering outdoors this year or next.

Good Growing,
Dr. E.R. Myers