How do we get Trichocereus cacti to the flowering stage?
Some thoughts here today on getting cactus to flower and a call for more advice and experience to that end.
I’m all about breeding trichocereus cacti to desired ends. In my apple breeding it currently takes about 7 years average to get a seedling to flower and produce fruit. That means 14 years for two generations. Do the math on a human life time. Yeah, it sucks. If there is any way to speed up the flowering of cactus, I’m all about finding it. Being 58, I kind of think now in terms of how many plant generations I have left to do breeding work. Of course the work and long term results are valuable whether I see the results or not, but I’d prefer to see the results ;) I’ve been told of a few possible ways to get cactus to flower.
small pots, with low fertility or imbalanced fertilization
One approach is growing in small pots. I’ve seen cactus growing in very small pots and not very tall that are flowering. Of course that does not say anything about how old they are. I don’t care if I can get a 20” cactus to flower if it takes too many years to get that 20 inches. Stress is an important factor in flowering in some plants and circumstances. Damage and disease in trees often induces flowering for instance. Of course natural selection would favor an organism reproducing before it dies of stress- one last hurra to spread its genetics. Reproduction in plants requires a lot of resources, but evolution favors spreading of genes, not just conservation and individual survival. The rationale for growing cactus in small pots would be to stress them, inducing flowering.
Growing a large plant in a small pot, possibly combined with inadequate nutrition or very skewed macronutrient ratios ought to be pretty stressful to the cactus. I grew out a scopulicola very fast, over 20 inches of fat growth a year for a couple of years, in a clay pot about 14” x 10” filled with pretty poor soil containing mostly inorganic grit, but a fair amount of charcoal. That was done by daily watering and peeing in the pot a lot since it was in a convenient location. It flowered in a couple of years, though it was already pretty old and stunted before I started pushing it to grow. I’m thinking my approach to this angle will be as follows.
*Grow out the plant quickly, with plenty of fertilizer and water, in small pots. If anything, lean toward high nitrogen ferts, which produces quick vegetative growth.
*Once it is pretty tall and the roots have filled out the pot, cut off fertilizer or more likely, just shift to high phosphorus fertilizers and water less frequently.
This approach assumes that the induction of flowering has nothing to do with slow stunted growth, or the age of the base plant, but rather with stress during a short period of time. That is just an assumption for the sake of the experiment. I just want to get them to run out of room for roots as fast as possible, then induce flowering by cutting off or shifting resources. The pots I’m using mostly are a common size which are about 9 inches diameter and maybe 12 to 14 inches tall. I would prefer shorter and slightly wider pots for stability, but I’m just using what I can scrounge up. I want to see the pot filled with roots and a good amount of top growth. Growing tops quickly should also mean growing roots quickly. More columns would mean more potential flowers. In a greenhouse environment I get some growth even through the winter, so the season is very long in a greenhouse here. That long season is only useful if they are getting the resources they need to grow fast though. If I were on the grid, I might consider adding some artificial light over a block of them at night to extend growing time.
grafting onto flowering stock
A possible method I’ve had recommended to me by Eliot from Cactus Jones is grafting onto already flowering stock. I’m fairly new to this game, so I have a minimal amount of flowering stock. What I do have has all been grafted over now to varieties that I want to use in breeding, like my seedlings King Tubby, Espiritu Cabra and Verity, some classics like landfill and a few other things I’ve picked up that seem promising. I should get good growth from those this year and ideally, I’d see flowering next year. Fingers crossed. The 2.5 foot long flowering cuttings I took from those were also grafted even before rooting.
Working with new seedlings, as I often am, might be a little different than working with clones that were taken from plants that have already flowered at some point. With many plants, certainly with apples, the new seedlings seem to be on their own schedule when it comes to flowering. Expedients like grafting onto an already flowering plant don’t seem to work well to induce sexual maturity. Typically, you have to grow them a lot before the sexual maturity switch flips and they start flowering. It is said that they need a certain number of buds on the plant before they will shift. There is a sophisticated method for doing this, where plants are grown under light 23 hours a day, at 70 something degrees in a high CO2 environment to get them to flowering stage in 1 or 2 years instead of 6 or 7. Something very similar might be useful for cactus, especially combined with growing out in small pots as described above. I just don’t know if cactus are the same as apples. I think they are likely different and that the benefit of fast growing might be more along the lines of filling out the pot quickly to get a big plant that is stressed by underpotting. My version of this will be to just grow out as quickly as possible in small pots. I’m even thinking of taking some cactus out of the large pots they are in and putting them into smaller pots! An advantage with cactus is that I’m not after the fruit and flowers themselves but just flowering from a select few seedlings the traits of which have already been observed. That is a huge advantage over fruit breeding, wherein the entire seedling lot is brought to flowering/fruiting.
light manipulation
Another idea I had was to try using light manipulation of some kind to trick or stress the plants. My main thought was to again trick the plant into thinking that something is wrong and that it needs to reproduce immediately.
It could also be that the formation of flower buds is day length dependent. That may be why flower buds develop at a certain time of the year. If that were effective, it might look like switching back and forth between limited light hours to simulate winter and then springtime day lengths to induce flower buds. Using light deprevation to induce flowering in cannabis is very common. Large greenhouses are completely covered with light proof plastic every day for a period of time. I think this is done several times a year to induce flowering in the same plants. It is kind of gross when you consider the amount of extra plastic used. In the case of cactus, this is a one time thing for small numbers of plants. We can produce thousands of seeds in one flowering, so only a small foot print of control would be necessary. That light control could be acheived in many different ways from one cactus, to a small room worth. Imagine for instance a 4 x 4 or 5 x 5 room that has both lights and light dep, to induce flowering is small numbers of potted cacti. Remember that all of this is for the sake of breeding generations of cacti more quickly. I can take a seedling to a large size quite fast already, but flowering does not seem to happen quickly in my experience so far. It may be possible to both grow promising seedlings and cuttings out fast and also make them think they are many years old, all in one year.
It might work to simply take large cardboard boxes and just put them over cacti for a day or two at a time, or maybe longer periods. If over heating were not a problem, maybe black plastic garbage bags over the plants would work on small spined varieties. Or maybe just randomly play with the light in a chaotic fashion, combining depravation with periods of exposure. Using certain colors of the light spectrum at different times might be useful too. My intuition is that any kind of chaos along these lines might induce early flowering in a plant. Remember, I’m not trying to grow nice plants, just induce flowering. Once the plant is flowering, it will probably continue if things are not changed drastically. My friend Will Tomlinson, who recommended the cactus in small pots method, says he thinks there is an opposite effect too though- essentially, that when repotting and shifting to abundant resources, they can go into high vegetative growth and pause flowering again. In the case of the tall scopulicola in the 14 inch pot I mentioned, the swelling roots cracked that pot apart. I have to repot it, but I’m going to put it in a smallish pot with crappy soil so that it will hopefully still induce flowering in the King Tubby and other grafts that I put on it. I have some PC grafted over as well. As long as they are not breaking out of the pots or tipping over constantly, I will not do anything different with them. If it ain’t broke…
Those are my current thoughts and plans. Any experience, observations etc. on inducing flowering would be appreciated.