Cultivation questions growers ask us most

We combed through hundreds of Office Hours Live episodes, pulled out the questions that come up again and again, and put the answers here for easy reference.

Looking for more in-depth answers? Listen to full Office Hours Live episodes here.

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What is crop steering?

Crop steering involves controlling plant growth through irrigation and environmental parameters. It uses strategic adjustments to watering frequency, nutrient concentrations, and environmental conditions to guide plant development towards desired traits.

How do you determine field capacity?

Field capacity can be determined by fully saturating the media, allowing it to drain, then measuring the water content. For most coco, field capacity is typically between 45-65% volumetric water content.

What EC levels do you recommend for LED grows?

For LED grows, EC levels are typically higher than HPS, often in the 3.5-4.0 range for feed EC. Root zone EC baselines under LEDs may reach 8-11 or higher due to increased light intensity allowing plants to use more nutrients.

How do you handle pH drift in coco?

Monitor runoff pH closely and adjust input pH as needed. Aim for runoff pH between 5.6-6.0 in coco. If pH drifts too low, raise input pH. Ensure adequate EC and frequent fertigation to help stabilize pH.

What causes tip burn on cannabis plants?

Tip burn is often caused by nutrient imbalances or pH issues rather than simply high EC. Check runoff pH first - it should be 5.6-5.9 for coco. Ensure adequate but not excessive EC. Consider tissue analysis to identify specific deficiencies or toxicities.

How do you determine proper dry back percentages?

Aim for 15-25% dry back between irrigations for most situations. Use sensors or weight measurements to track water loss. Adjust based on plant size, media volume, and growth stage.

What's the best way to root clones into final pots?

Use small, frequent irrigations to encourage downward root growth. Wait for 15-20% total dry back before fully saturating. Avoid overwatering early on. Consider using smaller media like rockwool cubes first, then transplanting to final pots once rooted.

How do you transition from stretch to bulking?

Wait until vertical growth slows significantly, usually 3-5 weeks into flower depending on strain. Gradually increase irrigation frequency and volume. Maintain EC levels. Adjust environmental parameters like VPD.

What VPD levels do you recommend for different growth stages?

Veg: 0.8-1.0 kPa

Early flower: 1.0-1.2 kPa

Mid-late flower: 1.2-1.4 kPa

Late flower/ripening: Up to 1.6 kPa to prevent mold

How do you deal with stretchy strains?

Use more aggressive generative steering early in flower. Maintain higher EC. Consider adjusting environmental factors like temperature differential. Group similar strains together. Be patient in transitioning to bulking.

What's the ideal pot size for crop steering?

1-2 gallon pots work well for most indoor grows. Larger pots make steering more difficult. Consider plant size, irrigation capacity, and growth duration. Smaller pots allow more precise control but require more frequent watering.

How do you determine proper CO2 levels?

General rule is light intensity (PPFD) + 200-300 ppm. So 1000 PPFD = 1200-1300 ppm CO2. Adjust based on plant response. Ensure other factors like VPD are dialed in.

How do you transition from veg to flower?

Gradually increase light intensity. Adjust nutrient ratios. Begin generative irrigation strategy. Adjust environmental parameters like temperature and humidity. Be patient, allow plants to acclimate.

How do you determine proper light intensity through growth stages?

Start clones at 150-200 PPFD. Gradually increase through veg up to 500-600 PPFD. Early flower 700-900 PPFD. Mid-late flower 900-1200 PPFD depending on strain and other factors.

How do you determine proper irrigation frequency?

Base it on plant size, media volume, environmental conditions, and growth stage. Use sensors or weight measurements to track water loss. Adjust to hit target dry back percentages. More frequent for veg steering, less frequent for gen steering. See also https://irrigation-calculator.aroya.io/

What causes purple coloration in cannabis plants?

Purple coloration can be genetic or environmental. Cold temperatures often trigger purpling, especially with a significant day/night temperature differential. Some LED spectrums may also encourage anthocyanin production. It's important to determine if purpling is a desirable trait or a sign of stress for your particular strain.

How do you handle runoff in crop steering?

Runoff is important for resetting the ionic balance in the root zone. Aim to get some runoff at least every 3 days, even when stacking EC. When steering generatively, you typically want less runoff to allow EC to build up. For vegetative steering, more frequent irrigation with runoff helps maintain stable EC. Always measure runoff pH and EC to guide your irrigation strategy.

What's the difference between P1, P2, and P3 irrigations?

P1 refers to the first phase of irrigation, typically in the morning, bringing the media to field capacity. P2 are subsequent irrigations during the day, used primarily in vegetative steering. P3 are night irrigations, which are generally avoided unless dealing with very large plants in small pots. The timing and volume of these irrigations are adjusted based on steering goals.

How do you clean and maintain your irrigation system?

Regular cleaning is crucial to prevent biofilm buildup and ensure even distribution of nutrients. Use of products like hypochlorous acid in your irrigation water can help keep lines clean. Between crops, consider more aggressive cleaning with appropriate sanitizers. Regularly check and clean filters, and consider using a chlorine dioxide fogger for thorough sanitization of the grow room.

How do you adjust your cultivation strategy for greenhouse growing versus indoor?

Greenhouse cultivation requires more adaptation to natural light cycles and outdoor temperatures. You may need to adjust CO2 levels, light supplementation, and irrigation strategies based on seasonal changes. In summer, managing heat and humidity becomes more challenging. In winter, you may need to increase supplemental lighting and adjust feeding schedules. Always monitor DLI (Daily Light Integral) and adjust your crop steering accordingly.

How do you determine the ideal EC (electrical conductivity) for cannabis plants?

The ideal EC depends on factors like growth stage, lighting, and genetics. Generally, for HPS lighting, a feed EC of 3.0-3.5 is common. For LED lighting, 3.5-4.0 EC is often used. However, it's important to monitor plant response and adjust accordingly.

What's the best way to manage VPD (vapor pressure deficit) throughout the flowering cycle?

VPD management typically involves starting lower (0.6-0.9 kPa) in early flower, increasing to 1.2-1.4 kPa during bulking, and then 1.4-1.6 kPa for ripening. This helps optimize transpiration and reduce the risk of mold.

How often should you water cannabis plants?

Watering frequency depends on many factors, including media type, plant size, and environmental conditions. In general, most commercial growers aim to water at least once daily, with multiple smaller waterings often preferred over fewer large waterings.

What's the ideal pH range for cannabis in different growing media?

For most soilless media like coco or rockwool, aim for a pH between 5.5-6.2. The exact range may vary slightly depending on the specific medium and nutrient uptake needs of the plant.

How do you prevent nutrient lockout in cannabis plants?

To prevent nutrient lockout, maintain proper pH levels, avoid over-fertilization, ensure adequate runoff to prevent salt buildup, and regularly monitor EC levels in both feed and runoff.

What are the benefits of using LED lights versus HPS for cannabis cultivation?

LED lights often provide more even light distribution, better energy efficiency, and less heat output. They also allow for more precise spectrum control. However, they may require different feeding and environmental management strategies compared to HPS.

How do you properly dry and cure cannabis?

Proper drying involves maintaining around 60% humidity and 60°F temperature for about 10-14 days. Curing then involves storing buds in airtight containers, opening them periodically to "burp" and allow gas exchange, typically for 2-8 weeks.

What's the best way to prevent and manage pests in a cannabis grow?

Implement strict sanitation protocols, use preventative measures like beneficial insects, maintain optimal environmental conditions, regularly inspect plants, and have an integrated pest management (IPM) plan in place.

What's the importance of CO2 supplementation in cannabis cultivation?

CO2 supplementation can significantly increase growth rates and yields, especially under high light intensities. Typically, aim for CO2 levels around 1200-1500 ppm, adjusting based on light levels (about ppfd + 250 ppm).

How do you manage humidity in a cannabis grow room?

Use dehumidifiers and proper ventilation to maintain appropriate humidity levels. Aim for 50-70% during vegetative growth, gradually lowering to 40-50% in late flowering to prevent mold issues.

What's the best nutrient regimen for cannabis plants?

A balanced NPK ratio with proper micronutrients is crucial. Many growers use a base nutrient line supplemented with additives like CalMag. Adjust ratios based on growth stage, with higher N in veg and higher PK in flower.

What's the best way to clone cannabis plants?

Take cuttings from healthy mother plants, use a rooting hormone, and maintain high humidity until roots develop. Proper sanitation and environmental control are crucial for successful cloning.

How do you manage stretch in cannabis plants during early flowering?

Control stretch through environmental factors like temperature differential (slightly cooler nights), light intensity, and irrigation strategy. Some strains may require more aggressive management than others.

What's the importance of proper air circulation in a cannabis grow room?

Good air circulation helps prevent mold, regulates temperature and humidity, strengthens plant stems, and ensures even CO2 distribution. Use oscillating fans and ensure proper HVAC design.

How do you properly feed cannabis plants in hydroponic systems?

In hydroponic systems, maintain stable pH and EC levels, ensure proper oxygenation of the nutrient solution, and regularly replace or top off the solution. Monitor plant response closely and adjust as needed.

What's the best way to manage a mother plant for consistent clones?

Keep mother plants in vegetative state under 18+ hours of light, maintain proper nutrition and pruning, and replace mothers periodically (every 6-12 months) to ensure vigor and genetic stability.

How do you prevent and manage hermaphroditism in cannabis plants?

Regularly provide adequate runoff during normal irrigations. If salt buildup occurs, increase runoff volume temporarily or perform a dedicated flush with pH-balanced water or a flushing solution. Monitor EC levels to ensure salts are being removed effectively.

What's the difference between phenotype, genotype, and chemotype?

These terms are crucial for understanding plant genetics and how different expressions of a strain can occur.

• Genotype: The genetic makeup of a plant, inherited from its parents. It determines the potential traits a plant can express.
• Phenotype: The observable characteristics of a plant, resulting from the interaction between its genotype and the environment. Different phenotypes can arise from the same genotype due to variations in growing conditions.
• Chemotype: Refers specifically to the chemical profile of a plant, particularly its cannabinoid and terpene content. Chemotype can also be influenced by both genetics and environmental factors.

How do I choose the right size drip emitters for my irrigation system?

The ideal emitter size depends on your pot size and desired irrigation strategy.

• Flow Rate: Aim for a flow rate of approximately 1 gallon per hour per plant. This can be achieved with multiple smaller emitters (like 0.29 gph or 0.5 gph) or a single larger emitter (like 1.0 gph).
• Redundancy: Using two emitters per plant provides redundancy in case one fails.
• Pot Size: For 1- or 2-gallon pots, 0.29 or 0.5 gph emitters are generally suitable. For larger pots, you may need larger emitters to achieve adequate flow.

How do I calculate the volume of water my plants will use so I can plan my irrigation system accordingly?

Estimating water usage helps you choose appropriate plumbing and equipment for your setup.

• Measure Dry Back: Track the weight difference between a fully saturated pot and a pot at the end of its dry back cycle. One gram of weight difference equals one milliliter of water used.
• Daily Usage: Divide the total water used by the number of days in the dry back cycle to get your daily usage per plant.
• System Capacity: Choose a system that can deliver the required volume of water to all your plants within your desired irrigation window.

How do I calculate the appropriate dehumidifier capacity for my grow room?

To determine the dehumidifier capacity, you need to consider the size of your grow room, the number of plants, and the desired humidity level.

1. Calculate the volume of your grow room: Multiply the length, width, and height of the room in meters.
2. Determine the desired humidity level: During flowering, aim for a relative humidity of around 40-60%.
3. Estimate the amount of water vapor produced by your plants: This will vary depending on the size and number of plants.
4. Consult a dehumidifier sizing chart: Many manufacturers provide charts that relate room size and humidity level to the recommended dehumidifier capacity.

It's generally better to overestimate your dehumidifier needs and then reduce the duty cycle if necessary.

What are the benefits of using two drippers per plant in a hydroponic system?

Using two drippers per plant offers several advantages:

• Redundancy: If one dripper becomes clogged or malfunctions, the other dripper can continue to provide water and nutrients to the plant, reducing the risk of crop loss.
• Even Distribution: Two drippers can help ensure more even distribution of water and nutrients throughout the root zone, especially in larger containers.
• Increased Flow Rate: Two drippers can provide a higher flow rate, which can be beneficial for larger plants with higher water demands.

I’m having trouble maintaining humidity levels during the drying and curing process. What are some tips?

Invest in a dehumidifier with adequate capacity for your drying room size. You can calculate the required dehumidification capacity by determining the total amount of water in the air (absolute humidity) and comparing it to your desired humidity level. Consider using a humidity monitor in your curing jars to ensure optimal conditions (around 60-65% RH). Regularly “burp” the jars to release excess moisture and allow for fresh air exchange.

What is the purpose of P2 (second watering) in an irrigation strategy?

P2 waterings are used to maintain a desired water content level in the substrate, especially during vegetative growth. While P1 waterings bring the substrate to field capacity, P2s prevent the substrate from drying out too quickly, ensuring consistent moisture availability for the plant. In some cases, P2s might be needed during bulking or ripening if environmental conditions or plant size necessitate additional irrigation.

How can I prevent larfy or airy buds and promote dense, high-quality flower production?

Several factors contribute to bud density and quality, including genetics, environment, and cultivation practices.

Choose strains known for producing dense buds. Ensure optimal lighting, temperature, and humidity levels throughout the flowering stage. Employ crop steering techniques like generative irrigation and proper dry-back to encourage tight internodal spacing and robust bud development. Avoid excessive defoliation, especially during flowering, as it can stress the plant and hinder bud growth.

What are the essential considerations for curing cannabis flower and how do I achieve a smooth, flavorful, and potent end product?

Proper curing is crucial for developing the desired aroma, flavor, and potency of cannabis flower.

After drying, trim and jar your buds at the appropriate moisture level (58-65% RH). Store jars in a cool, dark environment with consistent temperature and humidity. "Burp" jars regularly (once or twice daily) to release excess moisture and exchange air. Aim for a minimum cure time of three weeks, but longer cures (4-8 weeks) often yield superior quality.

Monitor humidity levels within the jars using hygrometers and adjust burping frequency accordingly. Consistent monitoring and adjustments are key to preventing mold growth while ensuring a slow and even cure.

What are the benefits of using substrate sensors in cannabis cultivation?

Substrate sensors provide real-time data on the growing medium's moisture content, EC, and temperature. This information allows growers to make informed decisions about irrigation, nutrient management, and environmental control, optimizing plant health and yield.

How can I effectively hand-water cannabis plants in coco coir?

Hand-watering coco requires careful attention to dry back and water volume.

• Monitor Dry Back: Assess the weight of the pot or use a finger test to determine when the coco is sufficiently dry.
• Apply Water Evenly: Use a gentle watering can or hand wand to saturate the coco evenly, avoiding runoff until the roots are established.
• Adjust Frequency: Water more frequently during early stages and less frequently as plants mature.
• Monitor EC and pH: Check runoff regularly to ensure proper nutrient levels and pH balance.

How long after harvest can powdery mildew spread from dried and packaged cannabis?

Spores may still be present: Even in dried and packaged cannabis, powdery mildew spores might exist.

Focus on prevention and cleanliness: Maintaining healthy plants, optimizing environmental conditions, and practicing strict sanitation protocols are crucial to minimize the risk of spreading powdery mildew.

What is leaf tissue analysis and how can it be useful?

Provides advanced analytics on nutrient composition: Leaf tissue analysis offers insights into the actual nutrient uptake and utilization by the plants.

Useful for strain optimization and troubleshooting: Can help understand the specific nutrient requirements of different strains and identify potential deficiencies or excesses.

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