Tan or tea-stained roots that are still firm

Likely causes, most likely first

Ranked for this sign on its own. Your stage, medium and readings change the order, so run the checker for your plant.

1. LikelyHarmless root staining (nutrients, tannins, additives)

   Root zoneLow urgencyRead: Brown roots in hydroponics (DWC, RDWC, NFT): a differential

   Fix: Nothing to fix if roots are firm, odourless and still growing white tips. Organic additives, humic products and some nutrient colours stain roots tan.

   Recovery: New tips keep appearing white; plant grows normally.

   How to confirm it

   • Look at the roots. Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining.
   • Smell test of roots, medium and reservoir. Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case.

2. Less likelyAmmonium toxicity (too much NH4 in the feed)

   Too much of somethingDeal with it this weekRead: Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets

   Fix: Keep ammonium at or below about 10-30% of total N (cannabis trials showed toxicity and lost yield above ~30%); switch to a mostly nitrate feed and correct root-zone pH.

   Recovery: pH stops falling and new leaves lose the dark claw within a week.

   How to confirm it

   • Measure input pH and root-zone (runoff or reservoir) pH. Calibrate the meter with fresh pH 7 and pH 4 buffers, then measure the mixed feed and the runoff (containers) or reservoir (hydro). Soil and living soil should sit at 6.0-7.0, coco, rockwool and peat mixes at 5.5-6.5, hydro at 5.5-6.2. Track 3+ readings; one reading is not a trend.
   • Look at the roots. Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining.

Look for

Firm, evenly tan roots with fine root hairs and white tips; no slime, no smell..