Nutrient Deficiencies in Cannabis
Nutrient deficiencies in cannabis are all too common; it’s not enough to simply give your plants food, you also have to make sure that they eat it – simply watering with a pH that is too high can cause your plants to stop absorbing nutrients and develop a deficiency.
Nutrient deficiencies in cannabis can happen for many reasons; you’re going to need to follow a series of steps to make sure that if your plants due show signs of deficiencies, you’re prepared to deal with them.
The first thing you’re going to need to do is regulate the pH of the water in your plants’ irrigation system. If they’re vegging then they’ll need a pH of 5.5/5.8 so that they can properly absorb nitrogen which is what they need during growth, as well as other nutrients in the soil such as calcium, zinc, iron and magnesium. Once you’re in the flowering phase you’ll need to progressively raise the pH level, from 6.0 to 6.8 which should be at around day 30 of the flowering period, and keep this 6.8 level until the end of the grow.
The second thing that you need to keep in mind is the water temperature when you water your plants – if it’s too cold the roots won’t be happy at all and they won’t be able to absorb the nutrients from the soil, and if it’s too hot then the concentration of oxygen in the water will lower considerably. Curiously, at 20-21º is when there’s more PPM of oxygen in the water, around 9PPM, so if you water using that temperature then you can be sure that your plants will absorb as much as they possibly can.
If you follow these steps you can rest assured that when your plants show signs of deficiencies, all they need is the right dose of nutrients, and there’s no need to worry about pH or temperature. Sometimes an excess of certain nutrients can cause blockage in the absorption of others, causing a deficiency. In this article we’re going to go through the most common deficiencies and how they manifest themselves in cannabis crops.
Macro-nutrient Deficiencies in Cannabis:
Macro-nutrients are those that we give our plants in irrigation water or by enriching the soil with natural fertilizers; these nutrients help create most of the cells in your plant which is why they’re the most needed one. The most important macro-nutrients are nitrogen, phosphorus and potassium. A deficiency of any three of these nutrients in your plants will cause them to stress out and eventually die if they don’t get enough.
This is seen on the plant through a general yellowing of entire leaves that starts in the middle of the leaf and extends outwards, leaving the veins in the leaf a deep green color until they’re eventually all yellow and they fall off. Just like many deficiencies involving macro nutrients, it shows up first on the biggest leaves. This deficiency can destroy your plants pretty fast, so it needs to be sorted out quickly. The best way to sort out this deficiency is to use a foliar spray that’s rich in nitrogen like Green Explosion by Top Crop so that the plant can begin repairing itself as soon as possible.
When plants begin the flower, especially at the start, they consume large quantities of phosphorus in order to grow the flowers. Before you can even notice, flowering will have stopped and the flowers will stop growing completely. The larger leaves will go a sort of dark purple color from the outside in and they bend downwards until they dry out and fall off. The best thing to do as soon as you see these signs is to add a little extra phosphorus to your flowering fertilizer. There are many different ones on the market, such as Canna’s PK 13-14, although if you want to prevent this deficiency you can use a powerful flowering stimulant at the start of the phase such as Bud Ignitor by Advanced Nutrients, which will also increase the amount of buds on your plant.
Potassium is one of the nutrients that are most needed during the bud fattening phase. When flowering reaches the point where the flowers are young and white still, they’ll need high quantities of this mineral to form thick pistils and buds, giving them the density and size they need. A deficiency of this mineral will prevent your buds from getting harder or denser; flowering will also stop and the buds will stop fattening. The leaves will begin to show brown and yellow stains, curling upwards. The best way to solve this is by using a proper fattening fertilizer such as Monster Bloom by Grotek. If you don’t want it to happen, use this fertilizer from the 4th or 5th week of the flowering period onwards.
Keep in mind that the leaves that have been damaged due to deficiencies will never recover, but at least your plant can get healthy again. The best thing to do is to prevent such issues, and if they happen catch them in time to avoid any nasty surprises.
Author: Javier Chinesta
Translation: Ciara Murphy