The Power of Comparison

A single grow diary tells you what happened. Two grow diaries side by side tell you why. When you can see that Grow A maintained VPD at 1.1–1.3 kPa throughout flower and yielded 0.95 g/W, while Grow B fluctuated between 0.7 and 1.6 kPa and yielded 0.62 g/W, the relationship between VPD consistency and yield becomes undeniable.

GrowVPD Pro includes a dedicated grow comparison screen that places two completed (or active) grows side by side, highlighting differences in environment, nutrition, techniques, and harvest results.

Using the Comparison Feature

  1. Open the Grow Diary tab
  2. Tap the comparison icon (two overlapping rectangles) in the top bar
  3. Select the first grow from the list
  4. Select the second grow to compare against
  5. The comparison screen displays both grows with parallel timelines

What to Compare

Yield Metrics

The most obvious comparison points: dry weight, g/W, g/plant, and g/m2. If both grows used the same tent and light, differences in yield are caused by genetics, environment, nutrition, or technique.

VPD Consistency

Look at the average VPD per week across both grows. The grow with more consistent VPD (smaller variance week to week) almost always performs better. Large VPD swings stress plants and reduce photosynthetic efficiency.

GrowVPD Pro shows the VPD trend line for each grow, making it easy to spot weeks where the environment was out of control.

Growth Speed

Compare the timeline from seed/clone to harvest. Did one grow finish faster? Check what was different in the early weeks — faster root establishment in the first 2 weeks often leads to earlier harvest dates.

PPFD Levels

If you recorded PPFD in your diary entries, compare the light intensity between grows. Higher PPFD with proper VPD and CO2 leads to faster growth and higher yields, up to the light saturation point of the plant.

Nutrient Schedules

Compare the EC/PPM values week by week. Did one grow receive heavier feeding? Were nutrients started earlier or later? Correlate this with the yield difference to understand your plants' appetite.

Training Techniques

If one grow used LST and the other used topping, or one was SOG and the other ScrOG, the comparison reveals how these techniques performed in your specific setup.

Tip: For the most meaningful comparison, change only one variable between grows. If you switch the light, change the strain, and modify the nutrient schedule simultaneously, you will not know which change caused the yield difference.

Learning from Differences

Pattern Recognition

After 3–5 grows with recorded data, patterns emerge that are invisible from any single grow:

  • Seasonal patterns: Grows started in November consistently yield more than those started in July (cooler ambient temperatures help late flower)
  • Strain behavior: Strain A always finishes in 8 weeks of flower; Strain B needs 10, and pushing Strain B to chop at 8 weeks reduces yield by 20%
  • Equipment impact: Upgrading from a blurple LED to a Samsung LM301H board increased yield by 35% with the same wattage
  • VPD correlation: Every grow where average flower VPD stayed between 1.1–1.3 kPa produced above-average yields

The Scientific Method for Growers

  1. Observe: Review previous grow data and identify the weakest metric
  2. Hypothesize: "If I maintain higher VPD during weeks 4–6 of flower, bud density will improve"
  3. Test: Run the next grow with this one change, keeping everything else the same
  4. Compare: Use the comparison feature to evaluate the result
  5. Repeat: Move to the next variable

Using Templates to Standardize

GrowVPD Pro's template system lets you save a successful grow as a template. On your next grow, load the template to pre-fill strain, medium, pot size, nutrient schedule, and target VPD values. This standardizes your baseline so comparisons are more meaningful.

When a grow based on a template outperforms the template baseline, update the template. Over time, your templates evolve into optimized recipes for each strain in your setup.

Tip: Name your grows descriptively. Instead of "Grow 7," use "Northern Lights Auto - 120x120 - Coco - 480W - Feb 2026." This makes the comparison list immediately informative without having to open each grow.