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In this guide you will learn
Once the leaves of your plants start touching, it’s time for them to flower. You do this by simply changing the light cycle to 12 hours of light and 12 hours of darkness. The plants will continue to grow for another couple of weeks, but will already produce flowering hormones.
Also check to see if your roots have sufficient room, because the plants still produce a lot of roots during this stage. If they don’t have enough room, transplant them to a bigger pot. You could carefully take an entire plant out of the pot to check and see.
The plants themselves also grow quite a lot during the first two weeks of the flowering stage. If the plants are already too close to each other, you could give them some more room by placing the pots further apart. Also take the height of the plants into consideration and make sure there’s always enough space between the lamp and your plants.
How to force plants to flower
Step by step
How to force plants to flower
- Replace your MH lamp by an HPS lamp if you have one
- Transplant your plants if your roots don’t have enough room
- Create some more space between the plants
- Set the time switch to 12/12
The only thing you have to do to start the flowering stage is to change the light cycle to 12/12. This means 12 hours of light and 12 hours of darkness. Make sure the room is completely lightproof, so not a single ray of light enters the room during the dark period. Also think about equipment that has a light on it, such as some power strips. If the plant is exposed to light during the dark period, it won’t flower properly.
I usually choose to have the lights on from 9PM to 9AM and to let my plants sit in the darkness during the day. The biggest advantage is that you can cool off your room more easily. During the day, when the sun is out and it’s warm, no lamps will be on. And at night, when it’s colder, you can better manage the temperature by letting fresh, cold air into the room when it gets too warm inside.
The flowering stage doesn’t start immediately after forcing your plants to flower. Your plant will produce flowering hormones during the first two weeks and will grow a lot to develop the flowering structure. The plant will get taller and the internodes (distance between the buds) is shortened. This looks more like a growing stage than a flowering stage, so take this into account when thinking about the nutrients you’re giving your plants.
Phosphor and potassium are true flowering fertilizers, but because your plants are actually still growing, they still need a lot of nitrogen. Wait a bit longer with flowering nutrients and keep giving your plants a lot of nitrogen-rich nutrients.
- Light cycle: 12 hours of light – 12 hours of darkness
- Light color: orange-red – HPS
- Temperature: 70 – 77 degrees
- Humidity: 60%
- Fertilizer: 1.0 – 1.2
- pH: 6.0
These plants are ready to start flowering. They have nice, big, green leaves that can catch a lot of light. You can still see the floor of the grow room a little bit, but it will be completely covered in about a week. The stems are firm and look healthy. They use more than 1/8 gallons of water a day, so the evaporation is also properly taking place. I set the time switch to 12 hours of light and 12 hours of darkness in order to start the flowering.
The plants will still grow a lot during the first two weeks of flowering. The changes in the light cycle cause the plants to produce different hormones that start the flowering stage. We’ll see the first small buds in about two weeks from now.
I now give them 1/8 gallons of water with an EC value of 1.0 every other day. Some leaves show a bit of discoloration so I’ll take it easy with the nutrients for a bit. I also hang the lamp a bit higher, because the plants have grown a lot.
Since the plants will continue to grow for now, I give them the same nutrients as before, which is rich in nitrogen. We’ll move on to flowering nutrients in two weeks. Here’s a bit on the most important nutrients for marijuana plants.
A plant creates its own food by converting water and CO2 into sugars and oxygen, with the help of light. In addition, there are some important elements the plant absorbs through its roots. The three most important ones are nitrogen (N), phosphor (P) and potassium (K).
Nitrogen is important for the production of chlorophyll, which is used to absorb light. It also promotes the growth of stems, leaves and buds. A plant therefore needs a lot of nitrogen during the growing stage.
Phosphor also plays an important role in the energy supply and respiration of the plant. It promotes the development of the roots of young plants and the flowering of mature plants. Phosphor is very important to your plants during the entire cultivation.
Potassium is a vital substance for the production and transportation of sugars inside the plant. It gives the plant firmness, makes it resistant to fungi and diseases and helps in the formation of the roots. In addition, it’s very important in the formation and growth of the buds. Potassium is therefore necessary during the entire cultivation, but the plant can use additional potassium during the last couple of weeks of flowering to create thick, hard buds.
There are other elements that are also important to your plants. Read the course Nutrients for marijuana plants for more background information on the nutrient needs of a plant.
The plants still look great and use a large amount of water. The temperature and humidity are also perfect, so these plants are thriving. I keep watering them every other day and keep the EC level on 1.0 for now and the pH at 6.0.
Last time I had some discoloration on the leaves and when I just opened my tent I saw some tiny bugs flying around. They look like flies, but they’re actually fungus gnats. The fungus gnats are harmless, but they lay eggs in your soil. The larvae that come out of these will feed on the roots of your plants, which could cause great damage.
I immediately put up some yellow flypaper and caught a decent amount of fungus gnats within a couple of hours. So there’s a big chance some larvae have been chewing on the roots of my plants, causing the discoloration on the leaves. I bought nematodes at the growshop and added them to the water (also available at Amazon at this link). These will kill the larvae and solve the problem.
I also hang some more fly strips, so the adult fungus gnats can’t lay any new eggs. Repeat the treatment after a couple of days to make sure all larvae are dead. If you want to know more about bugs, read the article on Most common marijuana pests. And feel free to ask your questions on the forum.
The plants are looking good. It’s always nice to notice that the temperature with the lights on doesn’t get too high and doesn’t get too low with the lights off. At a certain moment everything is set properly and nothing will go wrong, unless something breaks. The only thing you’ll have to worry about it is the temperature of the outside air you’re bringing into the room.
If it’s very warm outside, you suck that hot air into your growing room. This can lead to a too high temperature, especially when your lights are still on. It’s also not a good idea to bring ice cold air into the room when the lights are off. You can easily solve this by placing a small electric heater with thermostat in the room. Or by turning of the inlet during the dark period, since your plants basically don’t need any fresh air during this time.
Photosynthesis, build-up of sugars, respiration and growth all react differently to the temperature. A great example is the difference in sensitivity to temperature of photosynthesis and the growth of organs the produced sugars go to. Photosynthesis is quite insensitive to temperature within certain limits. For marijuana plants, this is between 59 and 86 degrees. So it doesn’t matter if it’s 62 or 81 degrees for the functioning of photosynthesis. The plant can create equal amounts of sugars at both temperatures.
But the distribution of those sugars from the leaf to the spots they’re needed is however sensitive to temperature. The distribution of sugars is inhibited when it gets colder than 68 degrees. A build-up of sugars will take place, which can be harmful to your plants. There are also processes that are less effective when it’s too warm. That’s why it’s always safe to keep your temperature between 70 and 77 degrees.
Read the part on Temperature and learn what influence temperature has on the functioning of your marijuana plants. This section also provides tips on how to increase or lower the temperature in your grow room.
The plants have now been flowering for a week, but there’s not that much to see. A lot of things are going on inside the plant and flowering hormones are being produced. They keep growing for another week, after which we will see the first little buds. You can see that it’s completely overgrown by now. The floor of the growing room is no longer visible, which is a good thing, because no light is being lost this way.
All light is therefore caught by the leaves and converted to sugars. The more light, the higher the yield. That’s why you use a reflector and reflecting walls, to send as much light to the plants as possible. If you’re still under 600 watt per 12 square feet, this is the moment to upgrade your lighting. It’s an easy way to increase your yield a bit.
The section on climate contains an article on the influence of light on your marijuana plants. This article explains what marijuana plants do with the light they catch. Photosynthesis, in which light is used to produce sugars, is obviously one option. But fluorescence is another one, which means that the electrons in the chlorophyll don’t convert the energy but immediately emit it. Read more at this link here.
Last week I had to deal with fungus gnats and treated these with nematodes to eliminate the larvae. I managed to catch quite a lot of fungus gnats with yellow flypaper last week, and they seem to be completely exterminated. But just to be sure, I’m adding nematodes to the water again and hang some new flypaper. Better safe than sorry.
All conditions are still perfect. The temperature doesn’t rise above 77 degrees when the lights are on, and doesn’t drop below 64 when the lights are off. The humidity stays between 50 and 60%, so that’s ideal. Since we cover some background information every day, I’ll teach you something about humidity this time. What is it and how does it effect your marijuana plants?
Humidity is the amount of moisture in the air, expressed in percentages. The humidity is very important to marijuana plants, because it determines the degree of evaporation. The lower the humidity, the higher the evaporation pressure, so the more water and nutrients your marijuana plants can absorb. But if the evaporation pressure gets too high, the plant will start to protect itself against dehydration and will close its stomata. This causes the plant to absorb almost no water anymore, thereby slowing down the growth.
So it’s important to create the right humidity in your growing room. Marijuana plants need a higher humidity during growth than during flowering, because the root system of young plants is a lot smaller. You can start growing with a humidity of around 70% and lower it by 5% each week until you’re at a humidity of 40%. You measure humidity with a hygrometer. Read the course about humidity for more information on humidity and marijuana plants.
The plants are still growing a little bit and I give them about 1/2 gallons of water every other day. I keep the pH at 6 and the EC at 1.1. As usual, the environment conditions are fine and the plants are looking healthy. And good news; the first buds are becoming visible.
If you look closely at the pictures above, you can see that there are some white hairs in between the new growth. These are the pistils of a marijauna plant, which are in fact the female reproduction organs. If these pistils are fertilized by the pollen of a male, the plant will start producing seeds. This negatively affects the quality of the weed, which is why we grow with feminized seeds or cuttings from a mother plant.
This is also the time to switch to flowering nutrients, so less nitrogen and more phosphor and potassium. I’m going to rinse the soil with tap water with a pH of 6. No nutrients. In this way, the plants can absorb the nitrogen-rich nutrients in the soil, creating room for more phosphor and potassium.
This is also a good time to measure the EC and pH values of your soil. They’ve been getting nutrients for a while now and you don’t want it to be absorbed inefficiently and accumulate in the soil, thereby greatly lowering the pH value. You measure the EC and pH of your soil like this;
Step by step
How to measure the pH of soil
- Mix 1 part soil with 1 part demineralized water
- Let it sit for 24 hours and stir it now and then
- Put it through a coffee filter
- Measure the pH value of the filtered water
Read the section about measuring the pH of soil in the article What is pH for a more detailed version.
A lot of little buds will develop over the next two weeks and they’ll start to grow nicely. Next time I’m giving them flowering nutrients and I’m placing sticks, because the plants will otherwise start tilting. Keep reading as much as possible about growing marijuana and post your questions to fellow growers on the forum.