A gardener tests whether plant cuttings root faster in dark glass vs clear jars. See an 8-week comparison, results, and whether darker vessels truly matter.
If you’ve spent any time in the houseplant community, you’ve probably heard a claim repeated over and over:
“Cuttings root faster in darker vessels because roots prefer darkness.”
It sounds logical. After all, roots naturally grow underground where they are shielded from light.
Many gardeners also say that darker jars help prevent algae growth, keep water cooler, and create a more natural rooting environment.
But how true is this?
Does the type of jar actually make a noticeable difference, or is it just another gardening myth?
To find out, a gardener in the UK ran an 8-week experiment comparing golden pothos cuttings grown in a clear glass jar versus a dark glass jar.
The results were surprising and incredibly useful for anyone who propagates plants at home.
This blog breaks down the entire experiment step-by-step, evaluates the findings, and explains what you should actually use for water propagation.
Clear vs. Dark Vessels for Water Propagation, What Really Works?
During this experiment, the gardener documented weekly changes from January to March, the peak of winter in England. Low light and cold temperatures naturally slow down root growth, making this test an interesting challenge.
But instead of dramatic differences, the results ended up showing something far more practical.
Let’s dive into the process.
Why Gardeners Believe Dark Vessels Are Better
Before the experiment, it’s important to understand why this myth exists.
1. Roots Naturally Prefer Darkness
In soil, roots grow in complete darkness. The theory is that a dark vessel mimics this underground environment.
2. Less Light Reduces Algae Growth
Clear jars allow sunlight to hit the water directly, which encourages algae.
Algae isn’t harmful, but it can make water change more frequent.
3. Darker Water Stays Cooler
Light warms the water in clear glass more quickly, while dark glass provides insulation.
4. Less Light = Less Stress
Some gardeners believe light exposure can “stress” new roots, slowing growth.
All of these reasons sound scientifically plausible.
But do they actually lead to faster rooting?
The Experiment Setup
Here’s how the gardener designed the experiment to keep everything as equal as possible.
The Jars
• 1 clear glass jar
• 1 dark-colored glass jar (not fully opaque but tinted)
Both were similar in size and shape, though not perfectly identical.
The Water
• Regular tap water
• Enough to submerge the nodes of each cutting
• Water was changed every 1–2 weeks
The Cuttings
• Golden pothos (Epipremnum aureum)
• 3 cuttings in each jar
• All taken from the same mother plant
• Limited by the narrow opening of the dark jar
The Conditions
• Both jars placed side-by-side at a sunny window
• Winter in England = cold, cloudy, low light
• Experiment lasted 8 full weeks
This wasn’t a scientific laboratory study — the gardener openly acknowledges the small sample size.
But it was consistent, controlled, and realistic for everyday plant owners.
Week-by-Week Root Development
Here’s how the cuttings performed over the 8-week period.
Week 1: No noticeable growth
Given the season (January), this was expected.
Cuttings root more slowly in winter.
Both jars showed identical results:
• No roots
• Healthy leaves
• No new growth points yet
Week 3: First signs of rooting appear
This is when exciting changes began.
Clear jar:
• 2 out of 3 cuttings produced new roots
Dark jar:
• 2 out of 3 cuttings produced new roots
So far, both jars performed exactly the same.
Week 4: All cuttings begin rooting
Clear jar:
• The final cutting began producing roots
• Early roots began to lengthen
Dark jar:
• Same pattern — final cutting rooted
• Roots lengthened similarly
• A few cuttings even showed early growth points
Again, no difference in speed or strength.
Week 6: Healthy growth continues
All cuttings were doing well except one.
• In the dark jar, 1 cutting focused more on growing a shoot than root mass
• All other cuttings across both jars had longer, stronger roots
• New leaves began forming in some cases
This difference was attributed to natural plant behavior, not jar color.
Week 8: Final evaluation
After 8 weeks:
• All cuttings (except one with a short root) were ready for soil
• All had healthy shoots and nodes
• Both jars produced almost identical results
• No major differences in root length, thickness, or speed
The gardener concluded:
There was no significant advantage to using a dark vessel over a clear one.
And that’s good news for anyone who struggles to find dark propagation bottles.
What This Experiment Really Proves
This mini study suggests that jar color does not dramatically affect root development, at least not for pothos, and not in typical home growing conditions.
You can root cuttings successfully in clear jars, dark jars, plastic cups, mugs, or even old food containers.
The most important factors are:
1. Water Quality
Clean water = healthier roots.
2. Light Levels
Bright, indirect light is ideal.
3. Temperature
Warmer weather = faster rooting.
(These cuttings were grown during winter, so summer results will be faster.)
4. Fresh Water Changes
Changing the water every 1–2 weeks prevents stagnation.
5. Healthy Cuttings
Choose cuttings with at least 1–2 solid nodes.
If these conditions are met, the jar itself becomes far less important.
Should You Still Try Dark Glass?
Absolutely, there are benefits:
• Less algae buildup
• Cleaner aesthetic
• Fewer water changes
• Some plants may prefer reduced light (hoya, philodendron, monstera)
But you shouldn’t feel pressured or overwhelmed.
The truth is simple:
Plants will root just fine in clear vessels.
This experiment proves it.
FAQs
1. Does jar color affect root speed?
Not significantly. This experiment showed nearly identical results.
2. Do dark jars prevent algae?
Yes, darker containers reduce algae growth by blocking light.
3. Is algae harmful to cuttings?
Not usually. It’s mostly just unattractive and may require more frequent water changes.
4. Do roots get stressed by light?
Not enough to slow growth for pothos. Some sensitive plants may see mild effects.
5. Should I root cuttings in winter?
You can, but expect slower results. Summer rooting is much faster.
6. Which plants benefit most from darker vessels?
Hoya, philodendron, scindapsus, monstera plants with sensitive aerial roots.
This 8-week experiment is a refreshing reminder that gardening doesn’t need to be complicated.
You don’t need special jars, tinted bottles, or rare containers to root plants successfully.
Whether you use:
• clear glass
• dark glass
• plastic
• ceramic
• recycled bottles
Your cuttings will grow as long as you give them good light, clean water, and time.
So if you’ve been saving kitchen jars for propagation, go for it.
Your plants won’t mind at all.
Ready to start propagating?
• Try rooting your next cutting in whatever jar you already have at home
• Share your propagation setup in the comments
• Let us know whether you prefer clear, amber, or opaque vessels
And if you found this experiment helpful, feel free to share it with another plant lover who might appreciate the simplicity.
Happy growing and may your roots be long, strong, and thriving.
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Visit DH Garden Centre today: where the holidays grow brighter, one plant at a time.
