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If Leaves Could Talk: Understanding and Avoiding Nutrient Deficiencies

Growing your own weed is an ideal way to ensure you’re smoking clean product. But cultivating is easier said than done. Here are some tips to help you understand what your crop needs.

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So, you’ve finally started growing. Congrats! But, things aren’t going very well because the leaves on your plants aren’t green. Thankfully, you’ve come to the right place: if your leaves aren’t a bright, healthy green it’s likely your crop has a nutrient deficiency. 95 percent of all nutrient deficiency symptoms show first on the leaves, which makes sense, considering the cannabis plant is mainly leaves. Root or stalk problems are rare, we’ve found. But before we get into specific nutrient deficiencies, we must first say a few words on pH levels and watering/feeding practices.

Proper pH is Essential

New growers: if you find yourself scratching your head and reaching for the pipe when asked about pH levels, don’t trip. You’re not alone, and we’ll get you up to speed. The pH of something (usually a liquid) refers to its acidity or alkalinity. The pH scale starts at 0 (very acidic) and goes to 14 (very alkaline). A value of seven is a neutral pH level. Cannabis likes a slightly acidic pH, so shoot for a pH of five or six in your nutrient solution. Marijuana plants cannot absorb nutrients properly if the pH at their roots is too high or too low. So even if the nutrients are present, you’ll still get what looks like nutrient deficient product if you don’t maintain the right pH.

While a purely hydroponic system would be cool to have, most growers stick to peat and perlite to raise their crop. It’s a low-cost, low-tech system, but your plants will love it. It only takes a week or so to find the right feeding and watering amounts in order to get the best yield possible.

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Water and Food Make for a Healthy Life

Most peat and perlite pots need to be fed and watered every two or three days. The general rule is to feed in the morning when the grow lamp turns on and water just before the grow lamp turns off. After a few days, if you notice the growing medium is wet an inch down you’ll have to cut back the amount of nutrient solution and water. Don’t confuse dead leaves and stunted growth with nitrogen deficiency– this can also be caused by being overwatered and overfed.

On the other hand, if your growing medium dries out before a full day has passed you’ll have to feed and water more often–but not more all at once. You might also want to ponder using a humidifier in the growing area. Sometimes a dry environment can cause symptoms like nutrient deficiencies, too. Wilting is the first symptom of an underfed, underwatered plant.

Consider the Nutrient Solution

Once you’ve perfected your pH and developed a good feeding and watering plan, think about the nutrient solution you use. During the green leafy stage of life, you might not pick up on a nutrient deficiency since the plant has all of the trace elements–zinc, boron, iron, sulphur, phosphorous and potassium–to grow healthily in its infancy. These trace elements are present in the seed, which lasts for the first two or three weeks of growth.

The concentration of the nutrient solution is as important as the pH of the nutrient solution. Nutrient burn is a reality most growers run into eventually. It is entirely possible to mix your nutrient solution at too high a concentration, referred to as parts per million (PPM), causing the tips of the lower leaves to brown and curl. Read the instructions on the container your nutrient comes in for the specific PPM the nutrient will deliver.

Thrive in the Perfect Temperature

Now let’s think about temperature and its effect on the nutrient solution, and thus, the plant as a whole. Cannabis likes a temperature of 22-24 degrees Celsius (or 68-75 degrees Fahrenheit). You can tell if a plant is heat-stressed if the leaves start folding upwards. The leaves will also have a sickly-looking dark green hue to them too. Just be sure not to confuse this symptom with nitrogen burn, which is an excess of nitrogen. It can look similar.

High temperatures can trigger root rot, too– a serious problem that can kill your plants over time. The easiest way to lower the temperature of an indoor space is to simply turn on a fan to move the air. The air will be cooled in a process known as vaporative cooling.

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Trace Elements

Observe the following table, which lists most nutrient deficiencies.

Nutrient Symptom(s)

ZincSulphur - The topmost leaves turn yellow. Lower leaves turn yellow. Yellow starts at the base of the leaf and proceeds to the tip.

Potassium - Brown or yellow edges on all leaves regardless of age.

Phosphorous - Brown spots all over the leaves. Affected leaves will die and drop off.

Manganese - Yellow veins, with brown spots.

Molybdenum - Older leaves turn an odd pink or red color.

Magnesium - Shows up on older plants. Also shows yellow between the veins of the leaf.

Iron - The topmost inner leaves turn bright yellow or even white.

Copper - Leaf tips appear yellow. The leaves are dark green.

Calcium - Brown spots that eat right through the leaf. Stems may be hollow and are brittle.

Boron - New foliage growth is very thick. Brown spots on the underside of the leaf.

Most nutrient deficiencies stem from a lack of trace elements. There are hundreds–perhaps thousands–of brands of trace elements, so you’ll have options (and some research to do). It should be noted that a good trace element bottle has a dark glass or plastic. The reason is because light bonds the chemicals in your trace elements. So, be sure to store the bottle in a dark place. Otherwise, the nutrients bond covalently and become unusable to the plant.

As your crop matures you’ll find that a budding plant needs tons of nutrients. The first deficiency you’ll notice is the yellowing and dying off of the older, lower leaves– this is a nitrogen deficiency. This is the most common ailment marijuana throws at you during the budding stage. We usually double the PPM of the nutrient solution during the budding stage. But keep an eye out for nutrient toxins.

With the right growing plan in place and handy articles (such as this one!), you’re sure to harvest a bumper crop of our favorite green growing thing: good ‘ol marijuana.

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