Cannabis seedling selection: why is it a bad idea

Some growers, those with more seedlings than space to grow them all, will attempt to select the best cannabis seedlings for onward growth. It’s a tricky challenge - trying to guess future differences in final yield, potency and terpene loading simply from a quick visual comparison of seedlings. Many growers assume the fastest growing or biggest seedling will become the highest-yielding or most potent adult plant. The problem, as experienced breeders are well aware, is that a seedling tells you very little about the adult plant it will eventually become.

Why growers try to select seedlings

Many growers will germinate a couple of extra cannabis seeds at the start of a grow to ensure they have enough plants to fill their grow area. Then, understandably, they find it hard to discard the surplus seedlings.

These observations seem superficially sensible. A vigorous seedling might look like a future champ. Unfortunately, the factors used above are poor predictors of the final result.

Why seedlings don't predict adult performance

Most of the traits that actually matter, like the quantity/type of cannabinoids, only appear later in the plant’s life.

None of these can be reliably assessed during the seedling stage. Early size or speed of growth often reflects nothing more than minor differences in germination timing, initial seedling growth rates or slight environmental micro-differences in the seedling tray. They rarely correlate with superior genetics once the plant reaches maturity.

Small differences between seedlings are perfectly normal

Slight differences in cannabis seed germination time, variable first-leaf size, temporary slower growth or different shades of green are completely normal. Healthy seedlings tend not to develop at exactly the same pace.

When should you start evaluating cannabis plants?

A thorough professional evaluation happens across the full cannabis life cycle:

This process takes months, not days. One advantage of the professional breeder over the home grower is the extra space they have to catalogue and clone each individual plant.

How professional breeders select exceptional plants

Professional breeders and geneticists evaluate plants over an entire lifecycle, often across multiple generations with different environments, before making selections. The professional breeder also tends to label each seedling and take at least one cutting before bloom. This allows the elite phenotypes to be kept for onward work. Lab analysis (cannabinoids and terpenes) is always used to identify the most potent and tastiest lines as well as allowing rapid identification of poor-quality lines to be immediately discarded.

Professionals look for stability, uniformity, yield, flower quality, resin production, terpene profile, THC levels, cannabinoid profile, disease resistance, stress tolerance and consistency. Only after repeated testing do they decide which genetics deserve to be kept and further refined.

Professional spectra fingerprinting of cannabis seeds and seedlings

One emerging new tool at the disposal of the cannabis seed professional is the use of advanced spectral fingerprinting, also known as hyperspectral seed imaging.

This promising new tech uses imaging to capture the molecular/chemical “signature” inside the seed. Combined with machine learning/AI, it allows the analysis of physical and chemical properties of seeds and correlates those signatures with observed traits after grow-outs.

Initial results are encouraging and allow increasingly accurate predictions to be made about the future of a seed or seedling. This ‘seed phenotyping’ technology has already been used to separate male/female seeds from a batch of regular seeds! The potential is exciting and scanning can also be used in the seedling stage.

Although the technology is relatively new it is already used in watermelon, sugar beet, tomato and some other agricultural crops. If spectral fingerprinting fully delivers with highly accurate predictive analysis, it will be another tool for cannabis seed professionals like Dutch Passion to use when creating superior autoflower seed and feminised seed varieties.

When should you discard a seedling?

Patience is one of the most valuable growing skills

Great cannabis plants often reveal their strengths and genetic superiority gradually. Giving every healthy seedling a fair chance significantly increases the likelihood of discovering exceptional genetics.

Plants that look average at two weeks can still become outstanding keepers by harvest. Rushing selection based on early appearance is one of the easiest ways to throw away potential winners.

If you bought quality cannabis seeds from a trusted source, then stay patient and have faith in the genetics.

FAQ - best cannabis seedlings