Other beneficial additions to feed

There are a number of other helpful but optional things we can add to help the health and growth of these cacti. These are not primarily nutrient focused, so note that these would all be in addition to a required nutrient fertilizer.

There are three main application methods. Foliar feeding, soil drench, and organic soil ammendments.

Misting certain products on the columns of these plants can allow them to absorb them through their open pores at night and provide an immediate hit of whatever product you're spraying them with. Some Trichocereus have a waxy outer skin that beads water - adding a small amount of a surfactant such as cocowet or aloe can prevent beading action and allow more even distribution of the spray. However you may see permanent disruptions of glaucous farina or staining when spraying darker or acidic products. Foliar feeding nutrient fertilizer can be a good solution for cuts that look like they need some nutrition but don't yet have roots, or plants that you don't want to wet their soil for whatever reason. Optimal timing of foliar feeding is from about 10:30p-3a. Spraying earlier in the day will do less than nothing, as the mist will evaporate before the window the plants pores are open and the remaining residue may block proper respiration. Some ways to apply a foliar feed are via a pump pressure sprayer, battery powered sprayer wand, or a diaphragm pump or a sump pump, hose, and a hose nozzle capable of producing a fine mist.

This is just a product you mix with water and water into your soil. You can mix into buckets and use a cup or battery sprayer wand to apply, you can pour the liquid into a tub and bottom water, or you can go larger scale and mix in a trash can and apply with a diaphragm pump or a sump pump, hose, and hose nozzle.

This includes a wide range of products such as earthworm castings, bone meal, insect frass, etc that are added to soil for nutrition and other reasons. For more info on mixing soil amendments into your substrate, check creating your own soil recipe.

Kelp products provide plant growth hormones that boost pupping. While this can be very useful if you want pups, feeding too often can result in too many pups which can slow the overall growth of your plant and lead to skinnier growth. Target the application for when you want pups. If you're feeding moderate to strong proper ratio synthetics, you won't need this very often. Kelp is not a significant source of NPKCaMg. Kelp is a popular choice to foliar feed. Alfalfa meal and blended aloe leaves are great sources of other plant growth hormones.

These are applied in a soil drench. They are aimed at providing beneficial microbes to the soil that will do various things including making nutrients more bioavailable, fighting off bad fungus and microbes, boosting the root zone soil's health. While they contain some NPK it's not complete or enough to provide nutrition on its own.

When applied in a soil drench, these will refresh aged soils that have been depleted or have gone hydrophobic, boosting the organic portion of your mix's water and nutrient holding capacities. They also work in symbiosis with kelp products to allow better absorption into the plant during foliar feeds, but they can stain and damage farina.

Applied via foliar feed, this boosts resistance to stressors such as extreme heat and UV by reinforcing cell walls and optimizing nutrient transportation. There are a wide range of qualities of these products. I can vouch for the top shelf monosilicic acid (MSA) products - they do work, but they are expensive. Best not to combine with anything aside from a surfactant, as it can react with some other products.

A family of beneficial fungus called Mycorrhizae bond with roots to create a support network for them, boosting nutrient and water uptake. The myco I have found that teams up the best with Trichocereus is single species Rhizophagus, sold as Mykos and Wallace's Organic Wonder. Single species means less competition and more complete colonization of the roots. You can purchase as a product you add to water and soil drench, or you can purchase as granules that you apply directly to roots during repotting. Trichoderma is a different class of fungi that attack other fungi, and are sometimes used to control hostile fungi, but Trichoderma will kill Mycorrhizae. Feeding heavy concentration synthetic nutrient fertilizers will also kill Mycorrhizae.

This is a product that contains a blend of kelp, humic acid, Mycorrhizae, Trichoderma, beneficial microbes and bacteria, proteins, and even Molasses which feeds these beneficial microbes. It's a highly effective root drench that kick starts a living soil's beneficial microbial ecosystem, but it's not cheap.