Best practises in cannabis cultivation are not universally defined and are therefore usually a function of experience or crossover from the cultivation of other plants. One area that lacks clarity and is causing problems in commercial facilities around Europe is the absence of proper practices for mother plant selection and maintenance.

Like many other areas of cannabis cultivation, best practices are often hard to define due to the many variations possible, unique approaches refined by individuals over years, and information hoarding. #

Mother Plant Selection 

On paper, it is extremely simple – however, the patience, time, and work required to successfully pick out a rare high-performing plant or unique chemovar is less straightforward than it may seem. The basic idea is to grow out a number of seeds, using cuttings (clones) from a number of selected individuals (seeds) to gauge the productivity of the mother (often called the ‘cut’).

Here is the first point of contention – “how many seeds are needed for a successful phenohunt?”

Unfortunately, there is no correct answer, as the stability and uniformity of a seed lot will undoubtedly play a part in this, as will the growing environment with indoor, outdoor and greenhouse all having slightly different requirements. It is also highly dependent on how rare a phenotype is required from the hunt, and the number of traits being targeted; fewer traits = easier to find, more traits = harder to find. 

Let’s start with the easy part of the scale – the upper-bound limit.

If time and resources were limitless, up to 100 seeds should be enough to find a handful of unique phenotypes, however, these might not have all the traits in one plant as desired, therefore it is not unheard of to go upward of this number and some breeders and nurseries will go all the way to 1000+ seeds. These numbers are done usually when the facility is only growing one cultivar and looking to match/replace or improve upon the current crop – in a greenhouse situation for example, if a grower wants the perfect plant and is seeking a specific cannabinoid ratio and highest cannabinoid concentration, whilst harvesting the optimal yield and maintaining physiology that requires as little hands-on management as possible. Let’s say they also require the plant to carry some tolerance to pathogen(s), then that type of rare phenotype may be in the 0.1% – 0.5% of a feminised seed lot. This means 1000 seeds should be planted, however, many growers going to this length will not use feminised seeds, and therefore start with 2000+ regular seeds. 

For some, this number of seeds for phenohunting can be considered excessive and requires a lot of space for the growing-out, as well as meticulous planning and tracking of performance. On the other side of the scale, seed packs of 10-20 will be enough to satisfy some phenohunters. This is often the case for smaller-scale indoor grows with hands-on plant training used to improve consistency and yields. Here, there is often less of a pathogen problem as they are usually closed-looped setups. The chance of finding a usable phenotype with fewer target traits to consider can be closer to 10%.  Of course, genetic uniformity is obviously a huge variable, and often the quality of the seeds varies from pack to pack. From the clandestine origins, a lot of the breeding for high THC, for example, has been carried out indoors and therefore less genetic traits are sought compared to those on a large scale growing outdoors or in a greenhouse. This makes it easier to find a suitable phenotype with high THC for indoors compared to, say, a greenhouse which requires additional traits along with the high THC.  

To put this into context when screening for viable mutant lines in a research capacity, it is not unusual to rack up thousands of lines in search of those one or two elusive rare gems.

This type of screening generally scales with the size of the organism for obvious reasons – space!

Therefore, when doing a bacterial transformation for example, and depending on the efficiency of the protocol, it is not difficult to spread out 10 petri dishes, each with thousands of colonies. Even with the model plant Arabidopsis thaliana, when, for example, creating a double mutant, it is not unheard of to screen hundreds of plants. Luckily, in most of these research examples, there are selection markers such as antibiotic resistance which are also conferred with the gene of interest/mutation to make it easier to find. With this in mind, the difficulty of selecting a handful of unique or impressive phenotypes is compounded by the lack of set standards to measure the plants’ output and the variation in growth rates from cultivar to cultivar. It is important to have a well-defined scoring system before beginning and to make sure consistency is built into the scoring system, as this makes it much easier to compare and eliminate underperforming plants. 

Let us assume the cut is selected, and now comes the job of readying the plant for production.

Depending on the grow plan, the testing space, and the number of workers, it is a good idea to test the mother plant’s production and recovery capabilities during the first flowering test. This will help ready the mother plant to bush out and create more lateral branching, test its speed of recovery, and give the grower a sense of how many clones can be taken in a defined time. The size of pot, pruning techniques, and environmental conditions will all play a role in influencing the plant’s ability to produce cuttings. Variety to variety and even cut to cut, differences are expected and mother plants will differ in what they can produce; this not a rule but more of a guideline – most mother plants fall into the range of 15-30 cuts per month. This is a wide range and it is possible to go under and over this range through mismanagement and optimisation respectively – however, as stated above, the variables on the input side also make a big difference, and 30 cuts per month isn’t achievable from a mother plant in a 300ml pot under low light with poor ventilation (for an extreme example of mismanagement). 

By the end of the first test flowering, the quality of flower produced and the recovery rate/production level of the mother is also understood. It is advisable to repeat this 2 or 3 times to prove consistency, and show that the first flowering test wasn’t an outlier or anomaly.  What is important to gauge here is the low-end output of the mother plant, and using that number to make plans for the filling of the production floor. It is better to have a healthy mother plant with extra options in terms of what branches to take for cuttings, rather than have a plant struggling to keep up with the rate in which cuttings are taken. Because it cannot be overstated, the environmental optimisation of mother plants should not be overlooked – they are easy to maintain, but this does not warrant complacency. The health of the mothers is reflected in the cuttings, and if a problem is undetected in the mothering room, it may be well into production before it becomes really obvious.  

 Assuming conditions are optimised and mother plants are healthy and happy, how long can this last? This is where the story fragments as there are a few schools of thought on this area, with a fair amount of overlap and options to suit different set ups: 

The Grandmother – One Mother to Rule Them All 

Keeping the same plant to mother your cultivation efforts is not unheard of. In fact, some growers maintain mothers for years, usually by sophisticated methods, to maximise longevity. This involves keeping the plant fairly small, and using its clones to generate more short-term mothers of the same line.  These ‘work-horse’ mothers are to fill the production floor leaving the ‘grandmother’ plant to fully recover and thrive for the next generation of mother plants. Maintaining mothers this way enables growers to stick with the true cut from which they found their favourite phenotype, whilst setting up a regeneration system to minimise the grandmother’s stress.  

Mother-to-Mothers 

Like the grandmother method, mother-to-mothers involves replacing the original mother plant with its first generation of clones, producing as many mothers as is needed to fill the shop floor. In this method, the original mother is not maintained to spawn the next generation of mothers. Instead, these new mother plants are maintained for several cycles, or as long as they stay healthy, however, this system usually needs a replenishment from the seed stock every year or so. Again, space, growth plan and personnel all influence which way is best for any given site. If a fresh phenohunt every year cannot be integrated into the grow plan (due to space, for example), it is worth reconsidering the source of replenishment and considering a different system. It is possible to take more clones from the cloned mothers and so on. 

The Dynasty – Mother to Clone to Mother to Clone 

Using a mother to create a clone which will become the new mother, and for that next generation of clones to become the next new mother, ad infinitum is common practice in commercial facilities in Europe and is, for this author, one of the worst ways to operate. It is common for this cycle to run down the generations with some facilities going mother to clone as much as 12-20+ times/generations, with some of these growers reporting no loss of vigour, potency or yield. This is the exception to the rule, and most suffer a drop in vigour around generation 4-7 – easy to miss as it can be gradual and, without scoring, may be harder to notice.

Continued cloning from clones will increase the rate at which the vigour can drop, and if exercising appropriate caution this should not be done long term, as any problems in previous generations will be inherited and the entire mother stock is at risk in this system. It can be done, usually by the most elite growers, otherwise any more than 3 or 4 generations often results in some type of phenotypic drift. This phenomenon, often mistakenly called genetic drift, is observed when this dynasty method is employed and with each generation, the build-up of pathogens, somatic mutations and natural senescence influences the phenotype usually resulting in drop of yield, lower cannabinoid production or a general drop in vigour. It can also be explained as a form of stress priming, where early exposure to a stress stimulus puts the plant on high alert for stress responses.

Although this can be utilised to condition the plant for various stresses when done in a deliberate fashion, the type of stress priming associated with sequential cloning is not the type that has a positive impact on the overall health of the plants/system. It is therefore recommended that this method be carried out for no more than 3 generations before replenishing the mother stock in order to keep the vigour high and the build-up of stresses low. On top of this, if a dynasty system is used, it is imperative to optimise everything and keep the mothers clear of all stresses. It is usually only the most experienced growers who can successfully accomplish this generation after generation, due to the complexity of the method. 

Outsourcing 

As each facility has a unique budget and system to maintain, working out a general cost analysis of outsourcing germplasm vs maintaining mothers internally seems a little counterproductive. Assuming proper due diligence is done on the supplier, the advantages to outsourcing clone supply generally include a 20-25% increase in flowering space (no longer required for internal nursery), shifting the reasonability of selecting, maintaining, and generating plantlets to a source that specialises in this area, and allowing all staff to focus on later life stages. 

Disadvantages include less control over phenohunting, a potential increase in adjustment time for arriving plants, recurring cost, and various potential pitfalls with delivery/shipping. 

Mother Maintenance Tips and Tricks 

Although nitrogen is important for new growth and a crucial part of a feed regime, between 10-20% less nitrogen should be given to mothers vs the same cultivar in vegetation for production. Too much nitrogen will cause stretching and reduce the strength of the branches which will form the stem of the new cutting.  

Defoliate regularly and make sure airflow is well managed. Newer growth is generally the best target to take cuts from as reversing shoot tissue into producing root tissue is easier in younger branches due to the higher level of meristem cells in fresh tissue. Although as is often the case, cultivar variation is the key here. Some cultivars will be excellent no matter where on the mother the cuttings come from, while others may be less so.  

Natural/organic feeding is a good way to keep mother plants healthy for longer. Organic or growing with the use of probiotics increases competition for detrimental pathogens and if done right will provide a strong basis for longevity.  

Sterility Matters 

Keeping good sanitary practices is crucial to minimising pathogen introduction. Cutting the mother plant creates an open wound and provides an easy entry point for pathogens. Use clean blades every cut, or at least every plant, with sterilising in between if needed. Simple ways to keep blades clean include steaming, alcohol (70% ethanol for example), chlorinated water wash, or using disposable blades.  

Keep the mother room extremely clean with a regular disinfectant such as fogging, as well as regular cleaning. 

Conclusion 

Making a good choice at the start of the process can save a lot of headaches later. Either obtain clones from a well-vetted source or make sure the mother room and growth plan are well organised. Always have backup options, especially if there have been problems in the past. If you cannot take regular cut clones cleanly, or there is a lack of in-house experience in this area, it would be advisable to consider outsourcing this stage of the grow.