CannaGLAP
Grow basics · 8 minute read · Updated October 15, 2026
How to keep a grow journal that makes your next grow better
Your third grow should be better than your first. Often it is not, because the lessons from the first one lived in your head, and your head forgot the details. What did you feed in week 5 last time, and how did the plant look a week later?
Why a journal beats memory
Plants answer slowly. A feeding change today shows up in the leaves several days later. A humidity problem at night shows up as mold weeks later. By the time you see the result, you have made five other changes, and you cannot tell which one did it.
A journal fixes that by turning "I think" into "I know". Penn State Extension puts it simply: a garden journal lets you review a garden's past, present and future. Iowa State Extension adds that over time you get a clear record of which plants thrived and which struggled, in your own conditions.
Your conditions are the point. A forum post tells you what worked in someone else's tent. Your journal tells you what works in yours.
What to log every time you check the tent
Keep the daily entry short enough that you will actually do it. Under two minutes is the goal.
| Item | Example | Why it matters |
|---|---|---|
| Date and time | Oct 15, 8:10 pm | Lets you line up cause and effect |
| Plant and stage | Plant B, flower day 24 | Day of stage is more useful than calendar date |
| Temperature, high and low | 79°F (26°C) / 68°F (20°C) | Spots heat spikes and big night drops |
| Humidity, high and low | 58% / 66% at lights off | Night humidity is where mold starts |
| Water or feed | 1.5 L, feed at half strength | The single biggest variable you control |
| pH in (and EC or PPM if you feed) | pH 6.4, EC 1.4 | Many deficiencies are pH problems |
| One line of notes | Lower leaves slight yellow | Early signs are easy to miss later |
Not watering today? Still log temperature, humidity and the one line. Gaps are when things go wrong unnoticed.
A min/max thermo-hygrometer or a Bluetooth sensor that keeps a history saves you guessing what happened at 3 a.m. Your targets depend on the stage; use our VPD by stage guide to see which temperature and humidity pairs fit each week.
Log events the day they happen
Events are the turning points you will want to find later. Give each one its own entry with the date and the plant.
- Germination, sprout and transplant dates, and pot sizes
- Topping, low stress training, defoliation, lollipopping
- The flip to 12 hours of light (day 1 of flower)
- First pistils, first signs of frost, start of the flush if you do one
- Any problem: yellowing, spots, pests, droop, male parts on a female
- Every fix you try, and what you used
- Gear changes: new light height, new fan speed, new nutrient line
- Anything odd: a power cut, a timer reset, a heat wave
When something goes wrong, the first question is always "what changed in the week before?" Event entries answer that in seconds. For example, if you find nanners in week 6, a logged timer reset in week 4 is a lead worth knowing about. See hermaphrodite cannabis and nanners.
Track pH and EC as trends, not single numbers
A single pH reading tells you little. A line of readings over three weeks tells you a lot.
Purdue University Extension's guide to testing growing media says it directly: measure and record pH and EC over time, because they change, and track them on a graph, which it calls the real value of testing. Its method for soilless media like coco, called the PourThru, goes like this:
- Water or feed as you normally would.
- Let the pot drain for 30 to 60 minutes.
- Set a saucer under the pot and pour on just enough distilled water to collect about 50 mL of runoff. Too much water dilutes the sample.
- Measure the pH and EC of that runoff.
We would add one habit of our own: write down how much water you poured on, because more water dilutes the reading.
Do it the same way, on the same day of the week, so readings are comparable. In soil you can check runoff too; the trend still matters more than one number.
What to look for: runoff EC climbing week after week usually means salts are building up, which can lead to nutrient burn. Runoff pH drifting out of range points to lockout. Keep the targets in view: soil 6.2 to 6.8, coco and hydro 5.8 to 6.2. Our pH and PPM chart has the full table.
Photo habits that make photos useful
Most grow photos are useless as records because each one is taken from a different spot, in different light. Fix three things:
- Same spot, same angle. Pick one position for each plant, for example front of the tent at canopy height.
- Same light. Purple or pink LED light hides yellowing and spots. If your light lets you, switch to white, or take the photo with a phone flashlight on, briefly, during lights on.
- Same rhythm. One photo per plant per week, plus a close-up any time something looks off.
Then a slow change becomes visible. Leaves that yellow a little each week look fine day to day and obvious side by side. If you are trying to name a leaf problem, our deficiency decoder shows what to compare.
A simple weekly review
Once a week, spend five minutes reading back. Ask three questions:
- What changed this week, in the plants and in the room?
- Did anything I did last week show a result this week?
- Is any number trending the wrong way: night humidity creeping up, runoff EC climbing, temperatures swinging wider?
Write one line of answer and one line of plan. "Night RH up from 55 to 65 percent since leaves filled in. Plan: defoliate lower third, raise exhaust speed at lights off." That is a journal doing its job.
The harvest review: where the real value is
After the harvest, before you start again, write a one-page summary of the grow:
- Strain, seed type, start and harvest dates, days in veg and days in flower
- Dry weight per plant, and how you dried and cured it (see our dry and cure guide)
- What went well, with the evidence from your logs
- What went wrong, and the date it started
- Three things you will change next grow
Penn State's list for gardeners includes successes, failures and plans, plus what you spent. That works for a tent as well. Over a few grows, these summaries become the most valuable grow guide you own, because they are about your space and your plants.
Paper, spreadsheet or app?
Any of them works if you use it. Extension advice for gardeners says the same: a notebook, binder, calendar or digital file can all do the job.
| Format | Good at | Watch out for |
|---|---|---|
| Paper notebook | Fast, no battery, easy to sketch | Hard to search, no graphs, photos live elsewhere |
| Spreadsheet | Graphs of pH, EC and climate | Clumsy at the tent, photos live elsewhere |
| Grow app | Logs, photos and sensor data in one place per plant | Check who can read your data |
That last point matters for a cannabis journal. It is a detailed record of what you grow at home. Canna GLAP keeps the journal end-to-end encrypted on your phone, so we cannot read it, and it tracks each plant from clone or seed to cure with its feed and water logs, photos and readings from Bluetooth temperature and humidity sensors. You can read how that works on is Canna GLAP safe. Whatever you choose, the habit matters more than the tool.
Questions growers ask
What should I write in a cannabis grow journal?
Date, plant, stage and day of stage, temperature and humidity highs and lows, what you watered or fed with its pH and EC, one photo, and any event such as topping, transplanting or the flip to flower.
How often should I update my grow journal?
A short entry every time you check the tent, a five minute review once a week, and a one-page summary after harvest. Short and regular beats long and rare.
Should I log runoff pH and EC?
Yes, as a trend. Purdue Extension recommends recording pH and EC over time and graphing them, because a single reading means little and the direction of change tells you what is happening in the root zone.
What is the best way to take grow photos for a journal?
Same spot, same angle, same light, once a week per plant, plus close-ups when something looks off. Avoid photos under purple light, which hides color changes.
Read next
- Cannabis pH and PPM chart by stage
- Cannabis feeding schedule basics
- Cannabis grow week by week: the full indoor timeline
- Hermaphrodite cannabis and nanners: spot them, then act
Sources
Education only, for adults 21+ where home cultivation is legal. Updated October 15, 2026.