Sucrose + citric acid baseline: 2% sugar, pH 4.5, no biocide
· Published 2026-08-28 · Vase solutions
This is the archive's control recipe. It contains exactly two ingredients and no preservative, which makes it the cheapest solution here and the one that most clearly demonstrates what sugar alone can and cannot do.
Sucrose 2 % Target pH 4.5 ±0.3 Change interval 24 h Available chlorine None mg/L Make at home Yes
| Component | Per litre | Role |
|---|---|---|
| White granulated sucrose | 20 g | energy substrate for the flower head |
| Citric acid (food grade) | 0.15 g | acidifier — lowers pH and slows vessel plugging |
| Sucrose | 2 % | Target pH 4.5 (±0.3) |
| Change interval | 24 h | Available chlorine: None |
| Make at home | Yes | none — this recipe relies on a daily water change instead |
What it does
Sucrose at 2% replaces the sugar the flower would otherwise draw from its own leaves and stem. Citric acid at 0.15 g/L drops the pH from a typical tap 7.4 to about 4.5, which slows the enzyme-driven blockage of the xylem and inhibits some, but not all, bacteria.
The measured effect on a garden rose: 5 days in plain water, 6–7 days in this recipe, with a 24-hour change in both cases.
- Dissolve the sucrose completely before adding the acid; adding acid first gives a slower dissolve.
- Stir until the solution is clear — undissolved sugar at the base of the vase feeds bacteria directly.
- Mix fresh every day; a batch left standing overnight at room temperature loses most of its value.
What it does not do
Without a biocide the bacterial population is only slowed, not controlled. At 22 °C this solution reaches the plugging threshold at about 40 hours, so the 24-hour change is not a recommendation, it is a requirement of the recipe.
| Water change interval | Vase life, garden rose | Water at day 3 |
|---|---|---|
| 24 h | 6–7 days | clear |
| 48 h | 4–5 days | cloudy, strong smell |
| 72 h | 3 days | opaque |
| no change | 2 days | foul, stem end black |
Practical notes
Do not use this recipe on hollow-stemmed flowers such as gerbera or delphinium without a biocide — the sugar feeds bacteria inside the tube where you cannot rinse it out.
Do not exceed 2% sucrose. At 4% the sugar actually pulls water out of the stem by osmosis in some species and you lose a day rather than gaining one.
Measured pH drifts up over 24 hours as the acid is consumed. Check with a strip if the batch is more than a day old.
20 g sucrose + 0.15 g citric acid in 1 L of water at 20 °C
