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Marijuana Vegetative Growth Pruning

Growing marijuana has two major stages: vegetative and flowering.  During the vegetative phase, your plants will establish a solid root system and full leaf development to prepare them for the final flowering phase, the actual marijuana buds.

Pruning the plant during the vegetative stage is when growers take the wheel from mother nature by manipulating the shape of marijuana plants to reap more benefits. In this article, we will see how marijuana plants develop during the vegetative stage and how to prune your plants safely.

What Is The Vegetative Stage

One to two weeks from germination, your marijuana plant will grow out from its seedling phase and enter its vegetative growth cycle. Unless it is an autoflowering variety, a marijuana plant will stay in the vegetative growth cycle if it is given anywhere between 18 - 24 hours of light per day.The vegetative phase is a crucial point at your plant’s life, as it will set up a root system and build up a strong core that will support it when it is the time for flowering and carrying big, frosty buds (hopefully!). Vegetation is also the time to implement all of your pruning and training techniques. But more on that later.The vegetative stage lasts about two to four weeks for most indoor strains and will be completed in the third to fifth month of growth depending on the marijuana strain and grow room conditions. Marijuana plants grow as fast as they can produce the energy required for new growth by photosynthesizing. The larger the leaves, the more efficient the photosynthesis.Under optimal conditions, a marijuana strain with good genetics can grow up to six inches per day! Once you are past the middle of the vegetative stage the number of blades on each leaf will decline, while the distance between two sets of leaves on the stem (phyllotaxy) will start to decrease.

Light In the Vegetative Stage

As long as a marijuana plant is getting less than approximately 11 hours of darkness per day, it will stay in the vegetative stage for as long as you want. The reason for this is because the plant responds to environmental change and will begin flowering when “winter” is approaching (daylight gets scarcer). So, in order to keep a plant healthy and happy in the vegetative stage, you must give it at least 13 hours of light per day. Decreasing that amount might trigger premature flowering and you definitely don’t want that!Many growers provide their plants with a full 24-0 light cycle (meaning a continuous day of light), without breaks. Others prefer an 18-6 scheme. In any case, this is largely a matter of preference and you can find more answers by looking at our light cycle article or by asking at the forum.The light spectrum is an important component of plant development, as marijuana “realizes” what’s going on in their environment by sensing the light colors. In nature, things are pretty standard: light wavelengths fluctuate depending on the season. However, as an indoor grower, you can manipulate the light spectrum to do your bidding! 
For example, if you are trying to keep plants relatively short and bushy, using blue spectrum light will aid them in their first few weeks. When the time for flowering comes, it is best to use red and orange bands of light. In their vegetative stage, plants require about 14% of the light spectrum to consist of blue light to prevent unnecessary stretching. Insufficient blue will lead to spindly, weak cannabis plants with long internodes (the vertical spacing between branches.)

Types of Indoor Marijuana Grow Lights

There is no shortage of options in your search for the perfect indoor marijuana grow lights. The main types of indoor grow lights are:

High-Pressure Sodium (HPS)

 High-Pressure Sodium grow lights are very intense and emit yellowish/red wavelengths of light, stimulating bud production. Therefore, many growers use them during the flowering stage, as their yield/Watt is better than any other type of indoor grow light. However, they tend to consume a lot of electricity and run very hot, meaning you will have to adjust their distance from your plants.

Fluorescent Lights

You can find fluorescent grow lights in many shapes and sizes: From short twisty bulbs (CFL) to long tubes (T5). Fluorescents are a great choice for small indoor gardens as they run cool, without using a lot of power. On the downside, they are quite weak and if you have a larger garden you might want to use them as supplemental sources of light.

Metal Halides (MH)

Metal halide lamps are great for the vegetative stage, as they emit light in the blue spectrum. Some people even use them all the way to flowering and harvest, but this is generally not advised. Metal halides will give your plant a much-needed boost over the vegetative period, so using one is handy.

Full Spectrum LED Grow Lights

Full spectrum LED grow lights are the best solution for beginner and intermediate cannabis growers, as they offer the perfect middle ground between power savings, versatility and light penetration. LED grow light fixtures are “plug and play”, meaning that no additional ventilation is needed as they have built-in cooling systems. You simply hang them above your plants and that’s it! A full-spectrum LED light will take your plant from seed to harvest without the need for supplemental lighting.

How much light do you need during the vegetative stage?

As with all plants, marijuana loves light, as it is their primary source of food. The more it gets, the healthier it is. Right? Well, yes and no.As we saw earlier, marijuana plants at the vegetative stage will thrive at an 18/6 or 24/0 light cycle. However, intensity also plays a major role, depending on your garden’s needs. For example, having a 1000W HPS grow light shining over two plants is not a good idea because much of the energy produced goes to waste. So, how much light is enough?To answer this, we need to know how much light a plant is getting if grown outdoors. Measuring the intensity of the light in lux, we can see that a day with low levels of sunlight can give about 30,000lux, while on a cloudy day these levels can drop lower than 10,000. On the other hand, places with constant intense sunlight can get levels upwards of 90,000lux.Cannabis plants generally do not have a problem with sunlight fluctuations, as long as they receive proper nutrients via their root system and the temperature stays relatively stable. However, the ideal lux levels for marijuana plants are:
  • 35,000 - 70,000 lux at the Vegetative stage
  • 55,000 - 85,000 lux at the Flowering stage.

Did you know?

Lux can be measured with specialized lux meters that you can obtain from Amazon or other marketplaces. Using one, you can accurately calculate how much light your plants are getting everywhere in your grow room.

Marijuana grow room conditions

Be sure to keep your grow room between 70°F– 85°F (21.1°C– 29.4°C) during the day. It is OK to have a 5-15 degree drop at night. Relative humidity should be in the 45 – 55% range. Also, be sure that your grow room or grow tent has adequate ventilation.  More about the correct temperature for marijuana.

Using Nutrients

Cannabis requires three primary or macronutrients for optimal health. These are Nitrogen (N), Phosphorous (P) and Potassium (K) or NPK. All plant-food labels include the percentage of these three elements in numerical form and are presented as N-P-K levels. The optimal marijuana nutrients ratios are up for debate, however, one thing is for certain: Manufacturers tend to largely overstate the benefits of their product for marketing reasons.  

Micronutrients are equally important, but only very tiny amounts are required and many, if not all, are readily available in potting soils without the need to add extra. If you are growing hydroponically, then these must be added regularly. These micronutrients or trace-elements are: Calcium (Ca), Magnesium (Mg), Sulfur (S), Manganese (Mn), Boron (B), Zinc (Zn),  Iron(Fe), Molybdenum(Mo), Chlorine(CL) and Copper (Cu).

The second biggest damager of your weed after overwatering is over-fertilizing. No matter how many times this is stressed, new growers seem to have the need to ‘push’ their plants. Excess nutrients will ‘burn’ your cannabis plants. A sure sign of nutrient burn is that the tips of most of the leaves will turn brown.

For very young plants (1-3 weeks) use nutrients at ¼ of the manufacturer’s recommended level and then gradually increase over to half of the recommended dosage. Note that every cannabis strain has different requirements and tolerances and that the manufacturer’s recommendations are only a guideline. If you observe your plants carefully, you will learn what they need. When it comes to nutrients, always err on the lower side to avoid harming your cannabis plants.

Pruning Your Plants the Right Way

The vegetative stage of marijuana plants is important because it is at this time that the plant takes shape and sets up a strong root system. It is also during this time that most experienced growers will try to prune their cannabis plants.

Pruning your marijuana plants is not mandatory, as the plant can grow in its normal "Xmas tree" shape. However, this shape means light distribution will be uneven and you’ll end up with big buds at the top that will gradually get smaller as you get to the lower parts. Careful pruning will ensure adequate light exposure throughout the plant, resulting in better yields and healthier plants.

When to Start Pruning Cannabis

You should start pruning your plants early in the vegetative stage when they are still narrow enough to be receiving all of the light throughout the foliage. As you start to prune and train your plants, you'll want to increase the canopy so the plant gets as much light as possible. You can prune your plants regularly until they reach the second week of flowering. Pruning past that timeframe can have adverse effects on your yield, as they will revert to vegetative growth to replenish their losses.

What to Look for When Pruning Your Cannabis Plant

There is a number of marijuana training techniques, but there are some basic principles behind successful pruning. The bigger, most resinous buds grow where the plant receives the most intense light and airflow. So, your focus should be to increase that area as much as possible. You can do that by:

  • Cutting low branches that do not receive a lot of light;
  • Cutting sickly leaves on the underside of the plant;
  • Cutting branches that are on the lower side of the plant’s stalks. 

How to Prune Your Cannabis Plants

To start pruning, you need some pairs of scissors of varying strength. Make sure they are sharp as you don’t want to tear the plant apart. The smoother the cut, the healthier the plant. Larger branches might need larger scissors. Also, depending on the training method you will follow, you might need a bowl of yarn.

Step-by-Step Guide to Pruning (with images)

Remove the larger stalks first to clear out some space before you get into finer work. You might think you are hurting your plants but you are actually helping, so be patient. Aim for the branches that are growing into the middle of the plant, right beneath the canopy, as they will never receive enough light.

After clearing out the middle section, you can work your way to the bud sites of the bottom and lower parts of the canopy branches. Although they are a part of a strong lead branch, they will not produce a high yield unless they receive enough light.

Remember that pruning is a form of training for your plant and works very similarly with how our body responds to exercise. Give your plant time to recover and don’t overdo it. In extreme cases, you can trigger a hormonal reaction from your plant including a growth inhibitor called jasmonic acid. If you have injured your plant, this hormone will put it in defense mode, severely stunting growth.

Pruning is an ancient technique and a great way to get more involved with your indoor marijuana garden. Pruning and plant training can make you a better grower and drastically improve your yields.

Some of the best-known training methods for cannabis crops are:

Switching to Flowering Mode

There are as many opinions as there are growers on that matter. Some growers switch at two weeks to create small, single bud cannabis plants, while others will veg their plants for up to four months to create higher yields. There are many possible answers and it all depends on your setup, goal, and patience.

It is important to note that your cannabis plants will ‘stretch’ or continue to add height after the flowering phase is induced by switching your light cycle regimen to 12/12. The amount of stretch is strain-dependent, but the general rule of thumb is that indicas will double in height, sativas will triple in height and hybrids will be somewhere in between.

Growing Example

Let’s say that your HID light must be no lower than 16” above your plants and your container size is 12” and the highest the bottom of your lamp can be is 84”’ and you are growing a sativa. Your actual vertical plant growing zone is 84” (lamp height) – 16” (lamp distance to plant) – 12” (container) height = 56” / 3 = 18.7”. This gives you the maximum height for your sativa plant before switching to flowering. In the same setup, an indica strain would require 56”/2 or a switch at 28” in height.

93 thoughts on “Marijuana Vegetative Growth Pruning

  1. mario says:

    ok, first time grower, i’ve been growing for 2 weeks and 3 days in soil, light is 5 watt pure white diod (heard diods were good and cheap choice). 24/7 light, pouring a little water 1 time per 2 days, i keep the soil a little wet. Anyway, all is good, i’ve got the 2 bunny leaves, 1 set of blade leaves, and 1 set just started growing. The problem is the height..its leaves are developing, but it’s height is not, almost 3 weeks and its about 5 cm tall …. is anything wrong? thanks

    • old timer says:

      Mario, you’re watering wrong. Marijuana likes to be wet then dry hence, you should water the crap out of them until there is visible water in the tray under the pot. Then do not water again until soil is thoroughly dry on top and just barely moist 2-3 inches down, now it is time to water again. Mine in 5 gallon cloth pots get watered about every 3-4 days, it depends on temperatures and humidity. I live in a dry climate so humidity is not much of a factor but temps. always are as it can get pretty cool at night here. If you keep the soil moist all the time you will develop fungus gnats (little black flies that live in the soil) guaranteed! Check the weight of your pot when bone dry then water it and observe the weight. When it is light add water. Also use a ph balanced nutrient like SensiGrow and SensiBloom. If you already have gnats, they will die out once the soil drys but you will need to kill the lava in the soil, do this by adding 16 oz. of hydrogen peroxide to a gallon of water and water with this the next time you water. This will kill the larva and oxygenate the soil.
      Good luck and Happy Growing

  2. Cosmoluckybear says:

    Mike.. You can vegetate your plants as long as you want . I have 2 indicas that I just put into flower, that are 6 months old! They are big bushy ladies and will have large Kolas!

  3. Bruno68 says:

    I have just started 4 auto feminized ,1st question what’s the difference between ‘auto’ and regular feminized. 2nd ,How often should I feed them have them on 16/8 under 600 watt hps

    • canbethewicked says:

      Bruno, auto’s don’t need a schedule to flower first thing is I grow autos at 24/7 for maximized size and continue through harvest that way. feeding is another story

  4. What kind of cfl light do i need for flowering?

    • Steve M. says:

      I used the same cfls through out the whole grow. But I used up to 96000lumis. Started with fewer, then added more as they needed. I had great results, fox farm soil. But it is strain based. Special kush #1 from royal queen seeds. Not lots of light penetration unless doing side lighting too. Still had heat issues, but live in a desert.

  5. Barbara Reynolds says:

    I planted seeds outside may 1. It is July 19th and my plants are 7 foot tall. Getting 12/12 sunlight. They all look like females from what i have gotten from u tube and google.I still dont have any flowering tho. My plants are huge but why dont I have any buds forming yet? 11 Weeks of vegetative stage seems long. And they are growing over my neighbors fence

  6. cw says:

    I have 3 plants that are about 5 weeks old and the are only 5/6 inches tall with a three leaf span I checked the temps lights and soil for nut.s and I have them on a 20/4 cycle is is normal for them to be this short?

    • M3G says:

      Sounds like you need a better light. Or if you do have a good mh or hid light, try putting it closer to your plants. Maybe that will work 🙂

  7. randy says:

    I have 6 plants under a 400 watt mh they r growing good they r 2 weeks old and r about 6 to 8 inches tall someone told mr to go ahead and switch to the 12/12 light cycle should I do that and also can I use my mh bulb for flowering and will a hps bulb work in the lamp I got the mh bulb in

    • canbethewicked says:

      you need to have a digital dual ballast lamp to be able to switch between mh and hps

    • luke says:

      It all depends on the type of ballast you have and whether or not the igniter is in the bulb or not

    • Elvis says:

      Hi there. When you switch to 12/12 is down to personal preference. You will be able to switch now, but the longer you wait the larger the yield will be. Have you thought about topping? If you pinch out the main growing tip, two tips will grow in its place and, with most strains, this will increase your yield.
      Your MH bulb is unlikely to be able to flower your plant successfully. Putting an HPS bulb in your lamp depends entirely on the make of lamp. You should ask the manufacturers. I have done it before with no problems, but when I asked that very question on a forum I was told that I risked causing an explosion! So I cannot tell you that it is OK. Just send an e-mail to the manufacturers and ask them.

  8. erik says:

    I’ve got a dwc bucket going. I noticed it got a few spots on it. When i investigated i noticed my ppm was very high so i did a water change using a little extra water on my mix this time. 2 day into week three and i’m have problems with my ppm raising on me again anyone know how to keep my ppm in range better.

    • Steve M. says:

      Are you checking before or after adding nutrients? Im doing a dwc too. I just do my water testing before. Tap water, distilled or reverse osmosis water for you? Im using tap water that sits a week before using and General Hydroponics flora kit. The water in my area is about 7ph out of the tap. I need 2 ml of ph down to bring it to where I need it. The indica is short and bushy and the sativa is tall and lanky. sjmatin54 at gmail.com if you want discuss more.

    • Elvis says:

      Are you having temperature issues? What temp. is the reservoir?
      Temperature affects the ability of your plants to take on nutes. It sounds like they are taking the water, but not the nutes.
      This is a complicated question that could be easier helped on a forum. Try joining the forum of this site (link on the bar above) and asking the question there….

  9. Dave says:

    Have two little plants about a week old they are about 3half inches high have to sets of leaves and an using flu resent uv bulbs have them at 25’c they are still small and in soil how long do I keep them on the uv bulbs ? When can I put them in my grow room with my 600w sodium light.? They are on 24hrs just now but when I put them under big light should I keep them on 24/24 or 6/18
    Any help would be great

  10. Chuck says:

    Actually, I was looking for a little info. What is the typical root ball size of a Indica plant. I was thinking about using a four qt. hydro. deep water system. I think I’ll be alright don’t you? Kind of stealth.

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