Helping your plant cuttings transition into the next stage of growth is critical and will impact the speed of growth, final yield, and quality. It is essential to manage climate, select a suitable substrate, and irrigate properly after transplant and well into the vegetative growth stage.
Climate conditions have a significant influence on a plant’s development. The environment where cuttings grow will not be the same as after transplant, and so they need to be acclimatized over the course of a few days. Failure to do so may shock the plants, leading to slower development and quality issues that can carry through the rest of its life cycle.
Humidity and temperature must be tweaked. Ideally, lighting intensity should be lower at the time of transplant, especially when switching from LEDs to HPS. When increasing the lighting intensity, do it slowly over a week before reaching the peak intensity for the vegetative grow-out stage. In small indoor rooms, this can be challenging or almost impossible, so consider keeping the cuttings in the veg room on a rack off to the side or under shade cloth.
Special consideration should also be given to the water content of the cutting plugs at the time of transplant. The moisture level should be even across the batch of cuttings, in the mid-to-high range of saturation. Avoid moving the plants if the WC is too low; doing so will stress them.
After completing the climate transition, select a growing media type and size. Some growers will go directly from cuttings into a large amount of media, the same volume that they will use to flower the plant. Transplanting into a large amount of growing media, like a 1-gallon (4 liter) container, might simplify the growing process, but can potentially slow initial plant development. Using a smaller volume of growing media, like a 0.125-gallon to 0.25-gallon (0.5 to 1 liter) pot or block, allows for more frequent irrigation without the risk of overwatering the developing root zone. These little blocks can be easily transplanted onto a Grodan slab and can be placed on top of the pot of coco or soil.
Initial Saturation of the new Substrate
The initial saturation of the growing media sets the stage for the root development of the plant. When hand watering, the flow rate needs to be adjusted based on the substrate being used. For Rockwool, repeated slow and steady applications ensure proper saturation. Depending on the block size, it may take up to six applications to thoroughly saturate the blocks. Applying too much water too fast can create air pockets in the blocks, leading to dry spots.
Flooding a table or using a large reservoir to soak the growing media is an effective way to saturate the blocks. If saturating multiple batches, dilute the solution and adjust the EC and pH when refreshing the tank between each one.
When using hydroponic growing media, it is recommended to add nutrients from the beginning. Ideally, saturate with a nutrient solution between 1.5 to 2.0 EC, with a pH of 5.5. When transplanting cuttings into a new volume of growing media, use the same nutrient solution you were using on the cuttings at a slightly lower concentration. This will help the cuttings root into the growing media.
The weight of the plugs, trays, blocks, or pots should be checked at initial saturation. Recheck the weight 24 hours later and at regular intervals to determine the best time to apply the first irrigation.
After transplant into a new substrate, the first few dry backs are the building blocks to creating a healthy new root system. The pictured chart shows the dry backs of a tomato transplanted into a Grodan small block. A Gosens sensor measures the amount of water in the block over nine days. The numbers shown are specific to tomatoes; these two large dry backs not only help the roots extend into the new growing media, but they also steer the plants toward generative growth.
In this case, it is best only to go this dry using larger blocks (4”+ high). Applying small irrigations frequently during the rooting-in and through the veg phase will help keep the plant active, especially when using a larger block. Using an irrigation system makes this much less time consuming than with hand watering. If watering by hand, apply a small amount of nutrient solution using a watering wand. Try applying these small irrigations several times per day. Once the plants have rooted through, add water based on the weight of the block or by measurements taken from a water content sensor.
The blue line is the rootzone WC
The red line is the rootzone EC
The green line is the rootzone temp
Irrigation for Vegetative Growth
An irrigation system is the only way to get consistent and uniform re-saturation. Flood tables and NFT systems that have shallow trays with a small water stream allow for an automatic irrigation process. They also help maintain uniformity.
Flood heights or drip times can be adjusted to apply the right amount of water to steer the plant. Hand-watering is possible during the grow-out phase but can create inconsistencies between the blocks that will carry through flower. When selecting an irrigation system for veg, make sure it has a high level of control. Flood systems should be able to flood at least halfway up the block. However, they should also be able to apply low floods that will not oversaturate the block, thus allowing for more frequent irrigations to speed up growth. With drip systems, growers should be able to apply small micro pulses that can be as low as 30mL per irrigation.
Each irrigation sends a vegetative signal to the plant. Consider how fast plants grow in aeroponic systems! Since the roots are grown in the air, the dry backs are much faster, allowing for more frequent irrigation that drives growth speed. If the goal is to develop the rootzone, dry backs are essential, especially when rooting into a new substrate volume. If the roots are leaving the block, it is most likely caused by too much water.
If you want the plants to develop and grow faster, implement a vegetative strategy. Small irrigations, typically 3% or less than the volume of growing media will do the trick. In flood systems, irrigate so water touches the bottom of the block. Ensure dry backs between irrigations (of at least 1 or 2%) and dry backs overnight (about 10% to 15%). The exact specifications depend on the environment, plant variety, size, and substrate.
For growers wanting smaller, more compact plants, a generative steer strategy can applied, which uses larger volumes with less frequency. In ebb/flood systems, flooding higher up the block less frequently is recommended. In drip systems, apply irrigation volumes of at least 6% of the substrate size. The timing of the irrigations will dictate the dry back. To steer toward generative growth, wait longer to apply the first irrigation of the day, and stop irrigating several hours before the lights go off. This should result in smaller, more compact plants with a better root system in the blocks.
The chart below shows how to apply a vegetative and generative irrigation strategy to Grodan small blocks (4 x 4x 2.5.). While the maximum wet weight (peak WC) stays the same, the dry weight is almost 100 grams less for the generative steering. The rest time between irrigations is used to steer the plants. The EC’s of the applied irrigation solutions are also adjusted to steer growth. High EC creates a generative steer, and lower EC a more vegetative one. Climate is also used in conjunction with irrigation as a tool to steer the crop.
Plant Spacing And Structure
Finally, the spacing and structure of the plants have a profound effect on uniform development.
Keeping the plants too close throughout the veg growth cycle will inhibit side shoot development and create tall, weak, and lanky branches. Plants must be spaced as soon as the leaves touch to prevent conditions for disease. Giving the plants more space allows the side shoots to receive more light and develop more vigorously.
Plants structured with different numbers of leaves and branches will uptake water at different rates. Excessive leaf removal and early pinching can create water uptake inconsistencies.
Happy plant steering!