Lollipopping and Pruning: What Happens Below Ground?

Cannabis growers usually judge pruning by what happens above the substrate. Topping produces more side branches, lollipopping removes shaded lower growth, and both techniques can change the distribution of flowers through the canopy. Removing shoots and leaves also changes the relationship between the canopy and the root system, although those effects are less visible.

Leaves supply much of the carbon used for root growth and maintenance, while roots supply the water and mineral nutrients required by the canopy. Plants continuously adjust investment between these two systems as their environment and architecture change. Heavy pruning can therefore affect more than the branches that were removed.

What do growers mean by lollipopping?

In Cannabis cultivation, lollipopping usually means removing branches, shoots and leaves from the lower part of the plant, leaving most productive growth in the better-lit upper canopy. Published Cannabis experiments describe a comparable treatment as removal of branches and leaves from the lower third of the plant.

The objective is usually to reduce poorly illuminated growth, improve canopy access and concentrate production in positions receiving more useful light. Topping is different: the main shoot apex is removed to suppress apical dominance and stimulate lateral branches. Both techniques modify above-ground architecture, but the amount of photosynthetic tissue removed can differ considerably.

Cannabis studies show that architecture can be changed successfully

Danziger and Bernstein compared several architecture treatments in drug-type Cannabis, including pruning and removal of lower branches and leaves. Removing lower growth improved chemical uniformity because the remaining flowers were concentrated in better-lit parts of the canopy. In a later density experiment, this lollipopping-type treatment again improved uniformity under dense growing conditions.

It did not, however, create a general increase in cannabinoid production per square metre. In the density study, total cannabinoid yield was not significantly changed by the architecture treatments.

More severe branch removal could have much larger consequences. In an earlier experiment, removing nearly all primary branches reduced inflorescence yield dramatically because active meristems and photosynthetic leaf area had been removed. Moderate pruning produced a very different response and could improve architecture and yield. The effect therefore depends heavily on what tissue is removed and how much of the plant remains productive.

The roots are supported by the canopy

Photosynthesis supplies carbohydrates not only to flowers and new leaves but also to roots. Growing root tips, root hairs, nutrient transport, respiration and interactions with microorganisms all require energy.

When a large amount of photosynthetic tissue is removed, carbon supply changes immediately. The plant can compensate by increasing photosynthesis in remaining leaves, using stored carbohydrate or allocating more resources toward rebuilding shoots. Those adjustments can reduce the carbon available for root growth.

This relationship has been studied directly in several other crops. After removal of mature leaves from young oak, root growth fell sharply and sugar concentrations in actively growing root tips declined. In wheat, defoliation caused visible root elongation to stop temporarily while the shoot canopy recovered. These responses reflect changes in below-ground allocation as well as the loss of leaves above ground.

A practical horticultural expression for the same process

In professional horticulture I was taught that the amount of plant above and below ground is related. After a crop is cut back hard, growers may describe it in Dutch as going “van de wortel af”, roughly meaning that the canopy has been reduced to a point where the existing root system is no longer maintained or used at its previous capacity.

That expression should not be interpreted literally as a fixed percentage of roots dying whenever the same percentage of shoots is removed. Plant responses are more flexible than that. When shoot demand and photosynthetic capacity suddenly decline, investment in roots can decline as the plant moves toward a new shoot–root balance.

Plants tend to rebuild a functional balance

Root-to-shoot ratio is not a fixed number, but plants commonly adjust allocation after one side of the system is disturbed. If roots are damaged, more resources may be directed below ground. If shoots are removed, the opposite response can occur while the canopy is rebuilt.

In winter wheat, defoliation stopped downward root penetration for approximately 20 days. Once canopy growth recovered, root elongation resumed at a similar rate to untreated plants, but the delay left the defoliated crop with a lower root density and shallower effective exploration of parts of the soil profile later in development.

Experiments in other species show similar changes in allocation. Defoliated citrus plants directed less carbon to fine roots, while severe shoot pruning in tree studies has reduced root carbohydrate reserves, respiration and root vitality. These responses are not identical between species, but they show how shoot pruning can influence root performance without physical damage to the roots.

Root loss and reduced root activity are not the same thing

Growers sometimes describe the effect simply as “roots die after pruning”. That can happen, particularly among fine roots under severe or prolonged reductions in carbon supply, but it is not a universal response.

In the wheat study, root growth paused without evidence that the existing root system simply died. In a large poplar defoliation experiment, nitrogen uptake fell strongly even though root production and root mortality were not significantly altered. Other tree studies have reported increased fine-root mortality after severe shoot disturbance.

Shoot removal can reduce carbon supply and shoot demand, after which root growth and metabolic activity may decline. Nutrient and water uptake can fall, and under sufficiently strong or prolonged imbalance, some roots may be lost. The intensity, timing, species and recovery rate determine how far this sequence progresses.

Water uptake changes for two reasons

After heavy pruning, water consumption often falls quickly. Fewer leaves means less transpiring surface, so the plant demands less water. Root capacity can also change.

In the 2024 wheat experiment, reduced root density following defoliation was associated with lower water and nitrogen uptake, particularly from deeper soil layers. The researchers were careful to distinguish reduced plant demand from reduced root uptake capacity because both processes occur together.

This distinction is relevant to container-grown Cannabis. After substantial pruning or lollipopping, a pot may remain wet longer simply because the smaller canopy is transpiring less. Continuing the same irrigation frequency immediately after removing a large amount of canopy can therefore produce a wetter root environment than before.

A home grower does not need a substrate sensor to observe this. Changes in pot weight, daily water use and the time required for the substrate to dry provide useful information about how the plant has responded.

Nutrient demand also changes

Removing actively growing shoots reduces nutrient demand, while reduced root activity can temporarily affect uptake capacity. Defoliation research in grasses shows that newly acquired nitrogen is preferentially redirected toward regrowing leaves while allocation to roots declines. Other experiments have shown that nitrogen and phosphorus already stored in roots can contribute to shoot recovery after defoliation.

A fixed feeding schedule may therefore be less informative immediately after major canopy work, when the balance between leaf area, growth and uptake has changed. That does not mean fertilizer should automatically be reduced after every pruning event. Moderate topping may have little effect on total canopy capacity once lateral growth develops. The useful observation is whether water use, growth and root-zone EC change after the intervention.

Lollipopping may be less disruptive than heavy defoliation

Lollipopping often removes shaded lower shoots that already contribute relatively little to whole-plant photosynthesis. Removing those tissues may therefore have a smaller effect on carbon supply than stripping large quantities of healthy, well-lit fan leaves from the active canopy.

Cannabis research supports part of this reasoning. Lower flowers in dense plants can receive much less light and show markedly different cannabinoid concentrations from upper flowers. Removing lower branches can improve product uniformity without necessarily reducing yield per area under the tested conditions.

That does not mean every branch below a chosen height is expendable. Lower shoots still carry leaves, and their contribution depends on canopy density and light distribution. A small indoor plant with good side lighting is different from a tall, densely packed crop where the lowest branches remain chronically shaded. The amount of productive tissue removed matters more than whether the technique carries the label “lollipopping”.

Topping produces a different type of disturbance

Topping removes relatively little biomass but eliminates the dominant apical meristem. The immediate change is therefore strongly hormonal as well as structural.

Reduced apical auxin influence allows lateral shoots to become more active, changing the distribution of sinks through the plant. Cannabis experiments repeatedly show shorter plants and increased lateral branching following topping. Depending on genotype and growing conditions, this can improve inflorescence distribution and sometimes biomass.

Because relatively little photosynthetic area may be removed during a simple early topping treatment, its below-ground effect is unlikely to resemble severe defoliation. Direct Cannabis measurements of root biomass or root activity after topping are still lacking, so claims that topping either stimulates or kills Cannabis roots would currently go beyond the evidence.

Timing changes the cost of pruning

A young vegetative plant has time to rebuild both canopy and root allocation after pruning. The same intervention late in flowering leaves much less time for recovery.

Developmental stage also changes where the plant is directing resources. During vegetative growth, new leaves, stems and roots are major sinks. During flowering, reproductive growth becomes increasingly important. Removing substantial productive tissue at those stages can therefore have different consequences even if the amount removed is similar.

Cannabis architecture studies show that the response to pruning depends on treatment timing, cultivar and plant size. Broader plant research shows the same dependence for root responses after defoliation. Removing the lower third of a plant describes a technique, but does not establish that it is optimal for every crop.

What this means in a home grow

Pruning should solve a defined canopy problem. Removing a weak, permanently shaded lower shoot is different from removing a large fraction of productive leaf area simply because the plant can survive it.

After a substantial intervention, changes in water use are especially useful to watch. If the container suddenly stays wet much longer, irrigation should follow the changed plant demand rather than the previous schedule. Stable new shoot growth and increasing water use indicate that canopy demand is recovering.

Large pruning events are also better separated from serious root-zone stress, severe drought or excessive EC. Shoot recovery requires carbon, water and nutrients, while the root system may temporarily be receiving less carbon from above. For a short-cycle crop such as Cannabis, repeated cycles of heavy removal and recovery also consume a meaningful fraction of the available production time.

Above and below ground remain connected

The practical rule I learned in horticulture, that hard pruning can cause a plant to go “off the root”, is useful as long as it is not interpreted as a literal one-to-one loss of root mass. Research in other species supports the broader mechanism: shoot removal alters carbon allocation, root growth can slow or stop temporarily, root nutrient and water uptake can decline, and severe or persistent reductions in carbon supply can contribute to fine-root loss.

Cannabis studies have so far concentrated mainly on canopy architecture, flowers and cannabinoid yield rather than root responses. They show that pruning and lollipopping can be useful management techniques, but their success depends on how much productive tissue is removed and what the grower is trying to achieve. Judging a pruning treatment therefore also means considering how the root system adjusts to the changed canopy.

References

Danziger, N. & Bernstein, N. (2021). Shape Matters: Plant Architecture Affects Chemical Uniformity in Large-Size Medical Cannabis Plants. Plants, 10, 1834. DOI: 10.3390/plants10091834.

Danziger, N. & Bernstein, N. (2022). Too Dense or Not Too Dense: Higher Planting Density Reduces Cannabinoid Uniformity but Increases Yield/Area in Drug-Type Medical Cannabis. Frontiers in Plant Science, 13, 713481. DOI: 10.3389/fpls.2022.713481.

Crispim Massuela, D. et al. (2022). Impact of Harvest Time and Pruning Technique on Total CBD Concentration and Yield of Medicinal Cannabis. Plants, 11, 140. DOI: 10.3390/plants11010140.

Han, E., Kirkegaard, J.A. & Thorup-Kristensen, K. (2024). Temporary growth cessation of wheat roots following defoliation. Plant and Soil, 502, 315–331. DOI: 10.1007/s11104-024-06547-4.

Dong, T., Duan, B., Korpelainen, H., Niinemets, Ü. & Li, C. (2019). Asymmetric pruning reveals how organ connectivity alters the functional balance between leaves and roots of Chinese fir. Journal of Experimental Botany, 70(6), 1941–1953. DOI: 10.1093/jxb/erz013.

Li, S. et al. (2024). Response of carbon fixation, allocation, and growth to source–sink manipulation by defoliation in vegetative citrus trees. Physiologia Plantarum, 176, e14304. DOI: 10.1111/ppl.14304.

Kosola, K.R., Dickmann, D.I., Paul, E.A. & Parry, D. (2001). Repeated insect defoliation effects on growth, nitrogen acquisition, carbohydrates, and root demography of poplars. Oecologia, 129, 65–74. DOI: 10.1007/s004420100694.