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!

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.

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:

• Screen of Green
• Sea of Green
• Low Stress Training
• FIMming

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