Black Runtz - Week by Week Grow Diary & Strain Review

Black Runtz turned into a strong, vigorous plant from early veg, handling training well and building into a productive indoor run.

There was a small setback early on due to old transplant soil, but once conditions improved, the plant bounced back quickly.

By flower, the main story was clear. Dense, compact buds stacked up well, the fruity Runtz aroma came through with a hint of citrus, and the thin stems needed support before harvest.

The grower finished the run with a very positive impression overall.

Grow Setup

Grow Diary

Weeks 0-1 - Germination & Early Seedling

Black Runtz was started directly in the substrate, and the germination stage went smoothly. The grower’s first note was simple: everything was fine.

By week 1, the seedling was established and sitting at 8 cm under an 18-hour light schedule. Conditions were steady with 25°C daytime temperature, 70% humidity, pH 6.3, and very light watering while the plant settled in.

Weeks 2-3 - Early Vegetative Development

Week 2 is where the run properly began to take shape. The plant had been started somewhat spontaneously, and the grower was initially unsure whether to keep it due to space limitations.

Once committed, the impression was positive from the outset, especially given the grower’s interest in Runtz genetics.

Week 3 brought the first real problem. Because fresh soil was not available at transplant, old loosened-up substrate was used instead. The plant showed a slightly pale tone, although growth stayed fairly steady and began improving.

During the same stage, the grower introduced a manifold, which caused some shock at first, but the plant recovered. Light was running at 300 PPFD, and only plain water was used that week.

Weeks 4-5 - Training Begins

By week 4, Black Runtz had fully bounced back and was looking strong again. It was transplanted into a large 15L fabric pot filled with Plagron Grow Mix, and the feeding schedule was switched fully over to Plagron nutrients.

Light ran at 400 PPFD, with one plain watering and one nutrient watering.

Week 5 showed strong continued growth. The plant was stretching vertically, which made training easier, and the grower planned to flip once the 8 main shoots had been spread further over the pot.

The only concern at this point was how much additional height the plant might gain in flower. Light was running at 500 PPFD during this stage.

Weeks 6-7 - Canopy Development & Transition to Flower

Week 6 was strong across the board. Black Runtz was growing vigorously, had handled all training well, and had been topped to 16 shoots with a very even structure.

The plant had shown a stretched growth pattern up to this point, and the grower hoped it would not get too tall in flower. The plan was to switch to 12 hours the following week.

In week 7, the light cycle was switched to 12 hours to initiate flowering. The plant remained healthy and continued growing quickly.

The grower described it as a cool genetic line, while also noting the continued stretched structure through the transition. Light was running at 600 PPFD, with one plain watering and one nutrient watering.

Weeks 8-9 - Early Flower Formation

Week 8 brought another strong stretch as flowering began properly. The plant held a great shape with lots of evenly tall shoots, but it remained slender and elongated overall.

The grower noted that it would likely be a great strain for a SCROG setup, although space limitations ruled that out in this run.

By week 9, flowering was progressing well. The plant had developed a bushier structure, showed a nice stretch, and formed plenty of flowers.

The shoots were on the thinner side, and defoliation and pruning were carried out during the week. The grower was already looking ahead to the coming aroma development.

Weeks 10-11 - Mid Flower Adjustments

Week 10 showed the first clear signs of the terpene profile arriving. The stretch was mostly over, the plant had taken on a beautiful shape, and flower production was fully kicking off.

The grower detected a faint fruity, runtzy aroma with a touch of lemon. Thin stems were already flagged as a likely issue once the buds became thicker and heavier.

In week 11, that support issue became more serious. The buds were gaining nice volume, but the plant could no longer really manage without support.

Even so, it remained healthy and had already developed some fine, fragrant terpenes. Light was running at 900 PPFD, with one plain watering and one nutrient watering.

Weeks 12-13 - Flower Development

Week 12 kept the plant moving in the right direction, but the structural weakness became impossible to ignore. Without support, it was already collapsing in on itself, and the grower expected stakes would be needed for the final weeks.

Aside from that, the plant was healthy, building momentum, and smelling increasingly good.

Week 13 pushed that trend even further. The buds became very heavy and firm, and strong support was essential to stop the flowers from hanging down.

The plant remained healthy, and the aroma intensified further, with a clearly fruity Runtz profile and a hint of citrus. Light ran at 1000 PPFD during this week.

Weeks 14-15 - Ripening & Final Stage

By week 14, Black Runtz was maturing very quickly. The thin stems were too weak for the compact, dense buds, and the grower was trying to let branches fall in roughly the right direction while watching trichome development.

It was clear the finish was close.

The harvest review was positive. The grower rated the run 9/10, said it would likely have performed much better in a SCROG setup, and noted that almost all of the buds turned out nice, dense, and compact.

The yield could have been higher, but the quality made up for it in the grower’s view. The diary records 93 days total and 230 g wet bud weight.

Detailed Observations & Grower’s Reflections

Black Runtz came across as a resilient and workable cultivar throughout this run. The early issue with poor transplant soil caused a temporary setback, but the plant recovered well once it was moved into a better medium and feeding routine.

The genetics also handled repeated training well. Main-lining, topping, and defoliation were all used across the run, and the plant responded by building an even, productive structure through veg and into flower.

The main takeaway from this diary is simple. This plant needed support in late flower. Heavy buds and relatively thin stems became the defining issue through the final stretch, and that remained consistent right into harvest.

Challenges & Solutions

The first challenge came during early veg when the plant was transplanted into old soil instead of fresh substrate. This caused pale colouring and a slight setback in development.

Once the plant was moved into a larger pot with Plagron Grow Mix and the feeding approach was adjusted, it recovered well.

The second challenge was the plant’s stretched structure. This made space management more important through veg and early flower.

The grower used main-lining, topping, and defoliation to keep the plant controlled and productive.

The final and biggest challenge was support in late flower. As the buds became dense and heavy, the stems could not keep up, so the plant needed support and branch positioning to stay upright.

Black Runtz: Final Result and Strain Review

Black Runtz finished this grow as a vigorous, trainable plant with a stretched structure, strong flower production, and a clear tendency to produce dense buds that needed physical support.

It was not a flawless run, but it recovered from the early substrate issue and finished with a strong quality-focused result.

The grower’s final verdict was clearly positive. The diary gives the plant a 9/10 rating and makes it clear that while yield could have been better, the dense, compact bud quality made the run worthwhile.

The grower also felt the cultivar would likely have performed better in a SCROG setup.

For growers looking at Black Runtz based on this diary, the clearest source-backed conclusion is that it showed good vigour, responded well to training, developed a fruity Runtz-forward aroma with citrus in flower, and needed support once the buds started putting on real weight.

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