Eutrophication, nutrient deficiency or spider mites?

We decided in June that it could be fun to try to grow some weed. So we got on the net and bought a feminized seed. We planted it in it's definitive pot, as advised by the seed seller. We planted it in a 16" pot, filled with a mix of store bought black earth, potting mix and sheep compost. It's been now about 5 to 6 weeks and the plant is almost 2' high.

Unfortunately, about a week ago, we started to see some tiny whitish discolored spots on the leaves, especially the ones at the base. We thought it was spider mites and started to spray the plant with a mix of 1 tbsp of natural dishwashing soap diluted into 1 gallon of water. We sprayed it daily for a week. the plant seemed to do better each day. The we fertilized it a bit with natural seaweed fertilizer (Acadie brand).

Two days after, the plant now have several brown spots and the tips of leaves are curling.

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Here are a bit more info on the plant:

Indoor/outdoor: Plant grown mostly outdoor (we put it under the sun during the day and bring it back inside at night)
Water: Mostly well water (with water softner), and sometimes we leave it under the rain outdoor
pH: I didn't ran any pH tests
Plant age: between 5 to 6 weeks
Type of fertilizer: Acadie seaweed fertilizer, diluted at 1 tbsp per gallon
Rate of application: every 2 weeks
Lighting source: natural sun, on the South facing side of the house
Air temperature: between 68F to 85F (with an average of 76F)
Air humidity: outside air has been quite humid I guess...
Lighting schedule: Outside, under the sun, from about 8 AM to 6 PM

It's getting worse day after day... Can't stand to see my plant dying like that and not knowing what to do! Anyone would have an idea?

It appears to be a nutrition problem. Because you haven't added anything that sounds toxic I'd guess that the pH is off and your plant is suffering from nutrient lockout.

Deffo NOT spidermites...

you should start in a small pot then when its well rooted go to next size up,
eventually getting to ur 16ltr if that's whast u want to use.
Plant dosent look overfed...
maybe try letting soil dry out a bit before feeding next.
all I can think is starting in your 16ltr pot the roots wudnt have filled it much you may be drowning them a bit.
do you use a wet/dry cycle on the soil?

Not sure what a wet/dry cycle is, but we usually wait until the soil is dry to touch before watering... Should I try to repot it in a smaller container? I watered it again this morning... Should I put it next to the dehumidifier to help draw the moisture out of the soil? How can I check the pH without watering it again? I'm concerned as today is even worst that yesterday :(

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to test the soil pH at this time, take out a quarter cup of soil, mix with bottled water and test. put it back in if you think the plant will miss it.

sounds like you may have caused the leaves to burn by spraying soap on them every day for a week. the waxy cuticle is only so thick and once removed the plants have no protection from the light. homemade concoctions may be cheaper than store bought products but store bought come with directions for use and quality control. Eutrophication by the way is a term used when excess runoff creates Algae blooms in ponds. over fertilization is what we say in the Hort industry and i assume you are asking about. if you do have mites, check out the thread "no more spider mites on cannabis"

Thanks for the clarification nicpett. I defenitely meant over fertilization. I have tested the water pH (I only had some pool water testing strips) and the water I've been using to water the plant has a pH between 6.4 and 6.8. I've tried to mix some of the soil from the pot with the water and test it again, it it indicates a pH of 6.4 or below (the chart isn't very precise).

As for the possibility of the deterioration due to spraying with water and soap, that is possible. However, we only sprayed it 3 days in a row, not a whole week. We did put the plant back under the sun afterward though.

The base leaves are slowly turning yellow. Since the pH is slightly acidic, could it be a deficiency in P, K or B ? Should I add some more fertilizer or something else to raise the pH?

Any idea on what I should do at this point?

Thanks!

What does the newest growth look like? Is it healthy or.... What is the mix they are in? There are so many variables to growing plants that often times it is very difficult to pin point a solution. A good old transplanting into a quality mix (I like foxfarm ocean forest) always seems to help. Is it even in a pot? How do the roots look if it is in a pot. Are they a healthy dental white or tanish/brown?

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Originally Posted by nicpett

What does the newest growth look like? Is it healthy or.... What is the mix they are in? There are so many variables to growing plants that often times it is very difficult to pin point a solution. A good old transplanting into a quality mix (I like foxfarm ocean forest) always seems to help. Is it even in a pot? How do the roots look if it is in a pot. Are they a healthy dental white or tanish/brown?

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It has been planted from the seed in a 16 inches diameter pot (the seed seller advised to plant it in its definitive pot). The soil we used is a mix of lightweight potting mix, regular garden black earth and sheep manure compost. The plant thrived in this soil until the plant reached about 2 feet tall.

The newest growth are not looking good (you can even see some in the pictures already posted). They are affected as well, with the tips dried out and curled up. The new shoot at the top started to wilt a bit since yesterday, and the base leaves are turning yellow. We let the soil dry out to make sure it's not over watering. It's now dry on top and slightly colder and darker soil 1 inch deep.

You choose to ignore PH at your own peril...You cannot properly diagnose a plant problem and NOT know the Ph of the water/nutes you feed it, the soil Ph, and the runoff Ph. If you want help, listen to the peeps like Shov that truly know and have experience with these weeds! And stop spraying soap on it...it's only making things worse, and not solving a thing. Ck the Ph and you will find the problem...start checking (and properly adjusting!) the Ph and you may save it.