Keeping Mothers And Cuttings Uniform Critical In Plant Steering

Written by Doug Jacobs.

Doug Jacobs is a Technical Advisor with Grodan. He provides expert consulting on proven Precision Growing methods to optimize crop production with Grodan Rockwool growing media and proper irrigation, producing the best quality plants using the least amount of inputs. He has experience with indoor, outdoor, and greenhouse hydroponics, vertical farms, aquaculture, and CEA system design, helping to design farms across North America. Doug showcases his passion and expertise as a feature writer in various national industry publications and as a conference speaker at US events.

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They say variety is the spice of life. While that is undoubtedly true for many things, when it comes to growing mother plants and cuttings in a greenhouse or elsewhere indoors, uniformity is critical for quality. The farm design and plant care plan should be developed with consistency in mind. 

Uniformity starts with mother stock and propagation. If you can repeatedly grow identical plants, they can be steered from the start of cultivation for maximum production. All subsequent inputs such as labor, climate, and irrigation can be optimized, delivering the highest quality plants time after time.

The Mother Load

Sourcing mother stock is an essential first step in creating a uniform crop. Whether you are getting rooted cuttings, seeds, or tissue culture plants, be sure they don’t carry any pests or disease and that they will deliver the final product you want. 

A test batch of plants can be created. Watch them grow through an entire lifecycle to determine how well they perform in your facility. At every stage, take detailed notes on the speed of root development, plant height, stem diameter, leaf and stem color, node spacing, and the natural structure of the plant. Also, observe the rootzone WC and EC measurements with climate conditions. These notes will help you determine the optimum spacing, irrigation and climate strategies, and the timing of labor.

Substrate Volume

But before growing the mother plants, select a substrate type, determine how much volume is needed for each plant, and the ideal planting density. Once these details are established, consider the irrigation requirements. Mother plants are typically kept in large amounts of growing media, usually 5 to 25-gallon pots, and are watered infrequently, one to four times per day if they are lucky. 

Having large mother plants in larger volumes of the substrate has some benefits and drawbacks. More substrate helps buffer out the irrigation system, so if your system fails or you don’t have time to hand water frequently, a large root zone can protect the plant. On the flip side, having large mother plants increases the risk of one bad mom spoiling several cuttings, therefore, reducing the yield of an entire crop.  

Use less growing media with a lot of space for root development. Make sure it has good water holding capacity and EC control. These factors allow irrigation to be used as a tool to steer and manage the growth of the mother plants, making them healthier and improving the quality of the cuttings they produce.

Vegetative And Generative Growth

What we are talking about is the balance between vegetative and generative growth. Vegetative is the growth of leaves and stems, while generative is the development of fruits and flowers. Both stages can be used to control how the plant grows throughout its lifecycle. 

If you want your mother plants to grow faster, implement a vegetative irrigation strategy by:

• Maintaining a higher overall WC in the root zone. 
• Having smaller dry backs between irrigations and overnight. 
• Using small shot sizes at a high frequency of watering. 
• Lowering EC at the dripper and in the root zone. 

To slow growth down, reduce stretching, and be more generative, do the following: 

• Decrease the overall WC in the root zone.
• Increase the dry back between each irrigation and overnight by delaying the first watering of the day and stopping before nightfall. 
• Decrease irrigation frequency while increasing the volume of each shot. 
• Increase dripper and rootzone EC with lower substrate temperatures. 

It’s essential to test these strategies while taking regular crop registration of plant height, node spacing, overall plant development, and health. 

Climate Steering

Like irrigation, the climate has a significant impact on how plants grow. Using different types of lights with varying intensities affect how the mother plants perform from propagation through flowering. Climate steering techniques need to be explored and utilized as a tool to manage plant growth. 

When taking cuttings, take note of the environmental conditions and how they affect the success of the crop. Having high light intensity, humidity, and temperatures has an impact on the health and success of the cuttings. Achieve better results by reducing the environmental conditions when taking cuttings.

Propagation: Sea Of Green

Smaller mother plants can grow at a very high density with just enough space so they barely touch. This sea of green helps the cuttings grow nice and straight and new ones to be taken without stressing the mother plant. 

Mother plants are grown to exact specifications with an equal number of leaves. After the mothers are planted, they need four weeks before they have about five fully expanded leaves. Once they are tall enough, pinch the head with a leaf to create a uniform crop structure across all the mothers. Keeping the number of leaves and branches even across all plants is critical for an even growth rate. 

The first cuttings can be taken two weeks after the first pinch. Subsequent flushes of cuttings can be taken weekly. During this process, you may end up with some taller plants that need to be trimmed back between harvests. Not all cuttings are taken in one day. It can take an entire week to take all of the cuttings during a flush to keep the mother plants in balance. 

As you go through each subsequent flush, maintain an equal number of leaves between each mother plant to keep them growing at a uniform rate. The perfect equation depends on what plants are growing. Some experimentation and crop registration will help determine the ideal number of leaves, the growth speed, and how many cuttings can be produced in a specific time frame.  

Between each harvest, look over the plants daily to ensure consistent growth. Remove leaves gradually to keep the plants equal and balanced. Mother plants are typically kept for a total of 26 weeks, which is especially true for cannabis. Keep in mind that the success of cannabis cuttings declines quickly over time. Given the limitations on what can be used for pest and disease control, it is good practice to change the mother plants every three or four months.

Tools And Tricks

To take the most uniform cuttings possible with the least amount of labor, “mum growers” use a special tool to help keep the cuttings the same length. This plastic tool uses a flat surface with a sharp edge that also supports the cutting as it’s being taken. Only new growth head cuttings are taken, and some amount of stem is left above the node to protect it so it can grow another cutting.

It is essential to have a precise visual scale for the size of the cuttings you want. Stem diameter groups cuttings as “Thick”, “Good”, and “Thin”. Cuttings can then be placed in batches together based on their growth rate. In addition to keeping stem length and diameter consistent, each cutting must also have the same number of leaves. 

Irrigation

The timing, frequency, and volumes used to irrigate cuttings have a tremendous impact on how the plants develop. Watering too early is the biggest problem for most growers. Determine the best time for irrigation by using weights of trays and individual plugs in combination with plant observations. Watch how much water is being applied after the first dry backs and work to find the optimum amount for developing the young cuttings. Growers who flood high up the side of the plugs and oversaturate the substrate tend to have problems with root development. Experiment with smaller floods or dips to keep the young root zone healthy. 

Wetting lines are popular in commercial agriculture because they reduce the need for expensive labor and various inconsistencies. At home or in smaller farms, manual watering booms and hand watering can be used. Still, the speed and flow of the water need to be adjusted based on the substrate being used. For Rockwool, repeated slow and steady applications should be made to ensure proper saturation. Applying too much water too fast can lead to dry spots in the media that will carry through the lifecycle of the plant. Inconsistent growth will affect the uniformity of growth. 

Flooding is also an effective, uniform way to saturate the blocks, but in large and multiple batches, take care to dilute the solution and adjust the EC and pH. Nutrients should always be used at the start with Rockwool. Ideally, saturate new plugs or block with a nutrient solution between 1.5 to 2.0 EC, with a pH of 5.5. I recommend using nutrients from the start for cuttings because Rockwool doesn’t provide any to the plant.

Weights of the plugs, trays, or blocks should be checked at initial saturation to ensure it was done correctly. Weights should be rechecked 24 hours later and at regular intervals to determine the best time to apply the first irrigation. After the initial saturation, the best way to maintain uniformity is through climate and irrigation. 

Climate Control

Climate has a significant impact on the development of the cuttings. Low light intensity, for example, slows plant growth and opens the plants up to diseases. High humidity is also another cause of poor growth. To achieve the best cuttings possible, experiment with systems and tools that help maintain humidity between 70-90% while keeping moisture away from the canopy. High heat and humidity levels lead to mold and mildew.  

Growers must be sure that the air and rootzone temperatures are not excessively hot and wet. Once that cuttings have established a root system, work to get the cuttings acclimated to the climate that will be used for growing. In commercial flower farms, use a clear plastic tarp to cover all the cuttings for the first week. Seedling trays are usually stackable for ease of movement and have built-in structure so the tarp can be placed and removed without disturbing the cuttings. Once the cuttings have started to root into the substrate, the tent is removed, and a misting system helps maintain humidity at the optimum range. 

In life, uniformity isn’t always a good thing. But when it comes to cuttings, nothing beats it. 

Happy growing!

Be sure to read part one of the plant steering series, Every Action Matters: The Ins And Outs Of Plant Steering.