Light Schedule for Clones: A Grower’s Guide to Strong Starts

If you’ve just got some cannabis clones, or you’re about to, one of the key setups to get right is the lighting. Too much light and they’re sluggish. Too little and you invite stress before they’ve even hit the ground running.

Let’s walk through a lighting schedule that works and give you some extra tips we’ve learnt so far.

Cannabis clones—or cuttings taken from a healthy mother plant - are in a delicate phase of development. These young plants aren’t seedlings, and they’re not yet established cannabis plants either. Instead, they’re transitioning: forming roots, building strength, and learning how to stand on their own.

At this stage, light exposure plays a critical role. It's the engine behind photosynthesis and essential for optimal growth. But without a solid root system to absorb water and nutrients, too much light can quickly lead to stress. That’s why dialing in the right light schedule for clones is key.

Clones need light exposure to get growing, but too much intensity can set them back. The key is creating a setup where light, moisture, temperature, humidity, and airflow stay in sync so each cutting can root without unnecessary stress.

For freshly cut cuttings, low-intensity or ambient light is best until roots start forming. Direct, high-powered light too early often leads to yellowing, curled leaves, and slow death - a classic sign of overexposure, not underexposure.

The right light schedule gives them a head start without pushing them too hard. Like any phase in the grower’s journey, success is about listening to the plant, reading the signs, and adjusting your setup to meet its real-time needs.

In the early stages, cannabis clones need gentle support. They’re still developing roots, adjusting to their environment, and figuring out how to grow on their own. At this point, growers often rely on low light intensity and extended light cycles. Sometimes up to 24 hours of light, or a more common 18/6 (18 hours of light, 6 hours of darkness). The goal is to encourage strong root growth without causing stress.

But if you’re buying clones from Homegrown, you’re getting a great head start. Your plant arrives in a rock wool cube, ready for transplant: rooted, stable, and primed for the next phase. That means your job starts with transplanting it into its final home and giving it the care it needs to settle in and take off.

Once transplanted, here’s how to keep your healthy clone on track:

• Light cycle: Stick with an 18/6 schedule. This gives your plant plenty of time to absorb light while still allowing for essential hours of darkness.
• Light intensity: Start with moderate intensity and don’t blast it right away. Instead, gradually increase the brightness over the first few days so your clone can adapt without stress.
• How much light: Focus on both quality and duration. The goal is adequate light that covers the canopy without frying it. Keep your equipment at a safe distance and adjust as the plant responds.
• Supplement if needed: If you’re relying on natural sunlight and the hours are short or uneven, add supplemental light to maintain consistency. Inconsistent light = inconsistent growth.
• Watch and learn: No two spaces are exactly alike. Don’t be afraid to experiment and fine-tune your setup based on how your clone responds. You’ll learn what works best in your space, for your plant.

Once your clones have developed a strong root system (typically after 2-3 weeks), it's time to transition them to the vegetative stage. This is an exciting milestone that indicates your clones are ready for more intense growth. Here's how to adjust your lighting for this new phase:

Increase light intensity gradually: Over a period of 3-5 days, gradually increase the light intensity from the clone range (100-300 µmol/m²/s PPFD) to the vegetative range (400-600 µmol/m²/s PPFD). This allows your plants to acclimate to the brighter light without experiencing shock.

Adjust light distance: As you increase intensity, you may need to raise your lights slightly to maintain the proper PPFD at canopy level. Monitor your plants closely for signs of light stress during this transition.

Change the light spectrum: If you're using a dimmable or adjustable-spectrum LED, you can adjust the spectrum to a more balanced ratio of blue and red light. A 50/50 ratio or 40% blue / 60% red is ideal for vegetative growth.

Maintain the 18/6 light cycle: The 18/6 light cycle (18 hours of light, 6 hours of darkness) is ideal for the vegetative stage and should be continued from the cloning stage.

Reduce humidity: As your plants transition to vegetative growth, gradually reduce humidity from the clone range (70-80%) to the vegetative range (50-70%). This encourages stronger root development and prepares the plants for the lower humidity they'll experience during flowering.

Increase airflow: Stronger plants can handle more airflow, which helps strengthen stems and prevent pest and disease issues. Gradually increase fan speed over the transition period.

Different setups offer different benefits for clone development. Understanding the basics helps you choose what works best for your space and budget.

• LED lights: These are a popular choice for many home growers. Modern LED grow lights are energy-efficient, run cool, and can be fine-tuned for specific spectrums. For clones, focus on fixtures that emphasize blue light, since this spectrum supports tighter node spacing and strong early growth.
  
  
• Fluorescent lights: Tried and true. Fluorescent lights, especially T5s, offer low light intensity that’s perfect for young, sensitive plants. They’re great for the earliest stages when cuttings are just starting to root. Easy on the plant, easy on your power bill.
  
  
• Blue wavelength focus: Whether you’re using LED or fluorescent, targeting the blue wavelength of the light spectrum can improve a clone’s growth rate and structural strength. This kind of direct light encourages compact, bushy development, exactly what you want in a young plant getting ready for vegetative growth.
  
  

The bottom line is: keep the light intensity manageable, choose fixtures that emphasize blue light, and remember: your setup doesn’t need to be high-powered, it needs to be dialed-in for this specific phase.

• Keep it gentle at first - low light intensity helps clones settle in without stress. Give them time and they’ll grow faster when they’re ready.
  
  
• Use the right spectrum. Blue light is the good stuff for early growth, helping your clones stay compact and strong before they stretch out to flower.
  
  
• Whether you're using soil or another medium, consistent lighting helps stabilize the process and sets your clone up to produce just like your other plants.
  
  
• Don’t rush it. Clones might take a couple of weeks to fully bounce back after a transplant. So adjust the light gradually and watch how they respond.
  
  
• Most of all: trust the plant, trust the process, and enjoy the ride.

Experiment with light levels to find what works best for your clones—providing more light can boost growth, but balance is key to avoid yellowing leaves or stunted development. Proper hours of light paired with sufficient darkness will help clones develop strong root growth and enter the vegetative stage ready for healthy growth and eventual flowering.

Even with a well-planned setup, you may encounter lighting-related issues. Here are some common problems and how to diagnose and resolve them:

Learning to read your plants is one of the most valuable skills you can develop as a grower. Here's what to look for:

Healthy Clones: Vibrant green leaves with a slight shine, strong stems that stand upright, compact growth with tight internodal spacing (small gaps between nodes), and new growth emerging from the top. The leaves should be flat and reaching toward the light without curling or drooping.

Light-Stressed Clones: Yellow or brown leaves, especially at the top of the plant where light intensity is highest. Crispy or brittle leaf edges that crumble when touched. Bleached or white patches on leaves directly under the light source. Stunted growth with little to no new development. The plant may appear to be "frozen" in place.

Stretching Clones: Tall, spindly growth with weak stems that may need support. Large gaps between nodes (internodal spacing of more than 2-3 inches). Pale green leaves that lack the vibrant color of healthy plants. The plant is reaching upward desperately searching for more light.

Heat-Stressed Clones: Leaves curling upward at the edges (tacoing). Dry, crispy leaf tips. Wilting despite adequate water. Rapid yellowing that starts at the top of the plant.

If you identify a lighting-related issue, follow these steps to correct it systematically:

• Step 1: Identify the problem. Use the information in this guide to diagnose the issue. Take photos to track progress and compare plant appearance over time.
• Step 2: Make one adjustment at a time. Don't make multiple changes at once, as this will make it difficult to determine which change was effective. For example, if you suspect light burns, move the lights further away but don't also change the light schedule or intensity at the same time.
• Step 3: Document your changes. Write down what adjustment you made, when you made it, and what the conditions were before the change. This will help you learn what works in your specific environment.
• Step 4: Monitor your plants. Observe your clones closely for 24-48 hours to see how they respond to the adjustment. Look for signs of improvement such as new growth, improved leaf color, or stronger stems.
• Step 5: Be patient. It may take several days for your clones to fully recover from a lighting-related issue. Don't make additional changes too quickly. Give each adjustment time to take effect.
• Step 6: Fine-tune as needed. Once you see improvement, you may need to make small additional adjustments to dial in the perfect settings for your environment.

Light intensity for cannabis clones should always be lower than that of mature plants—not to hold them back, but to prevent light stress and fuel steady progress.

Proper light intensity gives your clones just enough energy to grow without stunting root development. It’s the foundation for a healthy root system, which is key to optimal clone development.

Healthy roots boost nutrient and water uptake, supporting vigorous vegetative growth and setting the stage for a truly thriving clone.

Stay consistent. Tailor light exposure to the clone’s stage, and don’t rely on natural light alone if it’s not cutting it. The right start makes all the difference.