By the looks of it your plant has " Nutrient Burn "
Nutrient burn is one of the most common beginner cannabis growing problems. The yellow or brown leaf tips are caused by too-high levels of nutrients accumulating in the leaves.
Here is a pic of Nutrient Burn
(Nutrient burn is often called “Nute Burn” in the cannabis growing community).
When the roots take in more nutrients than a cannabis plant can use, the overabundance causes a brown or yellow “burn” on the tips of your leaves. If nutrient levels are not lowered, the burnt tips start traveling inwards and the ends of leaves start becoming crispy and twisted.
Take me straight to the solution for cannabis nute burn!
First sign of cannabis nutrient burn is often yellowing at the tips of the leaves
As nutrient burn progresses, the tips start getting bronze, crispy, curled and sometimes twisted. Although you can stop nutrient burn from getting worse, the burnt appearance won’t go away on the leaves that were already affected.
Burnt or brown looking tips of marijuana leaves means nute burn - this plant is in the flowering stage, which is when nute burn becomes more serious
Nutrient burn is most common when feeding cannabis too-high levels of bottled nutrients and especially chemical or mineral nutrients. This is what you’ll find in most non-organic plant food.
Mineral-based nutrients can help increase cannabis growth rates and yields compared to organic-based nutrients due to the fact that these nutrients are so easily absorbed by the plant roots. The plant doesn’t have to do any “work” to get the nutrients. The downside is your plant can easily take in more than it can use if the nutrient levels are too high.
Nutrient burn affects the tips of marijuana leaves. You may just see it on one or two leaves, or it can appear all over the plant.
Example of brown leaf tips from cannabis nutrient burn
Nutrient burn can also happen when plants or seedlings are grown directly in soil that has a high level of nutrients (a “hot” soil or growing medium) such as fresh compost, manure or a nutrient-amended soil mix. This usually happens to young seedlings, and they will “grow out of it” as they begin to use up all the nutrients in the soil, as long as more nutrients are not added.
In general, plants use overall higher levels of nutrients as they get more light. Therefore plants in relatively low light conditions can get nutrient burn at lower levels of nutrient than the same plant would under bigger grow lights.
Each cannabis plant is different, so you might have just one out of many plants get nutrient burn! That is completely normal.
Sometimes you’ll also see nutrient burn leaf tips also curl or “claw”. The clawing can be caused by an overabundance of Nitrogen (Nitrogen Toxicity), which is common for plants that are experiencing nutrient burn from overall high levels of nutrients.
Example of a marijuana plant with nutrient burn on the tips. The clawing is caused by a Nitrogen toxicity
Problem: You will notice the tips of your marijuana leaves showing the first signs of nutrient burn by turning yellow, tan, gold or brown. A light case of nutrient burn will only affect the tips of your leaves.
The yellow tips will eventually turn rusty brown and crispy. If you do not correct the problem, you may also notice the burn slowly spreading from the tips to the whole leaf. At this point, if you haven’t done so already, you should immediately treat your plant (directions below) before there’s more damage.
Brown burnt tips on leaves - The first signs of nutrient burn on a marijuana seedling
Nutrient burn can also manifest itself as brown or bronze spotting around the edges of the leaf serrations (often when there’s a problem with proper absorption of potassium), or with leaf tips curling downwards (tips pointing down is often associated with too much nitrogen).