Marijuana Cultivation/Fundamentals/Nutrient Selection and Maintenance
Nutrient Selection and Maintenance
Nutrient selection is a very important part of your growth plan. This book will not advocate any specific nutrient blend or mix but instead will cover nutrients in a more general manner.
There are three macro nutrients that must be considered when growing marijuana, (N) Nitrogen, (P) Phosphorus, and (K) Potassium. Almost every plant additive you look at will specify these numbers often in the format N-P-K without actually labeling which is which. These numbers really don't let you compare competing products effectively but they do show you the ratios of one macro ingredient to the next. During the different growth phases you will want different concentrations of these macro nutrients. During vegetative growth you will want high nitrogen and low phosphorus and during flowering you will want high phosphorus and lower nitrogen. It is worth busting another myth here. Many people believe that because there are separate vegetative and flowering formulas that having high P during veg or high N during flowering will hurt things. This simply isn't true. It is wasteful to throw away chemicals that are not needed and there is a maximum nutrient concentration that plants can handle without burning roots. This means that you wouldn't want to trade P for N during flowering. But most flowering formulas actually contain enough N that they could be used during vegetative growth.
There are also a number of micro-nutrients needed for growth that must be present. Many major fertilizers for soil do not contain these micro-nutrients because they assume it will be provided in the soil. Always use hydroponic nutrients for hydroponic growing.
Regardless of what nutrients you use, they will be mixed with water. The water you use should ideally be reverse osmosis treated or if tap water is a must then make sure to let it sit out overnight to let any chlorine contained in it evaporate. This is a deceptive thing in that chlorinated tap water will work fine but will prevent your plant from ever reaching its full potential. This is a great place to squash the rain water myth. Rain water is full of minerals, dirt, and living organisms it is neither the best nor the worst choice for growing plants. In particular if you are using an indoor grow or hydroponic rig you will not desire to use rainwater since it will contain heavy amounts of minerals that you did not intend to add to your carefully controlled growth system.
Dry vs Liquid
Liquid nutrients are very trendy and hip in the hydroponic world. There is nothing wrong with a Liquid nutrient, you know it will mix well but they are generally more expensive because the bottle contains more water and less nutrient. This also makes them more expensive to ship and transport. When it comes time to mix them and feed your plant either dry or Liquid works equally well.
In both cases you should add to the water after filling the container rather than adding nutrients and then filling. Adding before filling can lead to nutrient imbalances.
Nutrient salts will build up in soil it is highly recommended that you flush your soil plants with clean water from time to time. If in a pot flush with 3 times the volume of the pot with water and for plants in the ground flush until the ground is fully saturated and possibly repeat the following day. This is also recommended if the plants show signs of nutrient or ph imbalance.
Maintaining a Reservoir
Proper maintenance of your reservoir is essential to growing healthy marijuana to its full potential if you grow using a hydroponic method that requires you to keep a res. The critical factors here are nutrient levels and PH. Unfortunately, there is no simple way to track the level of individual nutrients in your reservoir but there are ways to keep a healthy reservoir system going just the same.
To begin, you will want to mix your nutrients at full strength according to the manufacturers recommendations. You should use either reverse osmosis treated water or if you must use tap water draw it from the cold water tap and let your water sit overnight to evaporate chlorine. Hot water will contain more dissolved impurities than cold water. After adding your nutrients and micro-nutrients you should adjust your PH to 5.8 which is ideal for hydroponic nutrient solution. Measure the TDS, or total dissolved solids with a TDS meter. With full strength nutrient solution this number will probably be around 1100-1300 TDS. This will be where you want to keep your nutrient (if using lower strength nutrient for earlier stages then mix and measure TDS accordingly).
Now all you need to do is top off your nutrient solution with clean water daily. If your TDS is low then add nutrients. If your PH is off then adjust it.
Since the plant will not absorb nutrients in the same proportions you are adding them imbalances will result over time. To correct this you will periodically need to drain and fill your reservoir with fresh nutrient solution. To begin with do this at least once a month and just before you start flowering. During flowering change the reservoir every two weeks. How often you actually need to do this depends on the plants, the nutrients, the size of the reservoir, etc. Luckily the plants will let you know how often you need to do this. They will start exhibiting signs of nutrient deficiency when there is an imbalance and you will know that you can't go longer than that before changing the reservoir. Especially with clones you will be able to get res changes down to a system of clockwork since the clones will generally all have the same nutrient preferences.
PH Ideals and Adjustment
The ideal PH for your garden is based on nutrient uptake. A PH that is too low will be too acidic and burn the roots of your plant. A PH that is too high will be too alkaline and cause your plants roots to be unable to uptake nutrients. Many supposed nutrient deficiency problems are really caused by improper PH levels. PH can be tested with a digital meter (ideal), or with chemical drop tests or test strips. Because PH optimally should be adjusted to a tenth of a point accuracy a digital meter is highly recommended.
Depending on your method of grow and whether you are using soil or hydroponic different nutrients will be absorbed at different PH levels. For a hydroponic garden the only PH level that all nutrients will be absorbed at is 5.8. For soil gardens the ideal PH is 6.5.
Leaving tap water to sit out overnight will evaporate chlorine and raise PH. Adding nutrients will lower PH. But once you have done those things how do you move the PH to where it needs to be?
There are a couple simple ways to do this. There are commonly sold chemicals known as PH up and PH down sold at hydroponic gardening stores that will adjust PH for you. Similar chemicals are also sold for pools but these are not recommended for plants. But the easiest method can be found in your kitchen. Simple baking soda and distilled white vinegar will adjust PH up and down respectively. These should be used in very small amounts. You might need to play with them to find what is needed for your water source and nutrients (it should remain consistent once you've found what you need to add). I find that in a 4 gallon flowering nutrient mix 1/2 tsp is enough to raise the PH from 5.0 to 5.8.
PH adjustment chemicals should be added after all nutrients. After adding PH adjustment chemicals mix well and then give your water a couple hours for everything to stabilize. If you are using baking soda and vinegar then try to avoid using them in combination. Use either one or the other if possible. They will react with one another to form CO2. CO2 is great for plants leaves and flowers but is bad for plant roots.