Rooting Hormones v 2.0 - ignore the weak pretender below

[TimN]

What I’ve learned about rooting preparations for plants.

For the past few years I have used some sort of rooting compound when planting bare-root cacti or when rooting cactus cuttings and offsets. It has always been a random process for me -- buy some rooting compound, apply it somehow, and hope for the best, but I kept thinking there HAS to be a better way.

The plants I’m buying lately are more expensive and harder to come by than when I first started collecting and cultivating cacti, so I figured I'd better do some research on this subject.

What I found is that, like many things in life, there are no concrete answers. My objective is to develop a method or set of guidelines for handling bare-root cactus plants or cuttings to maximize survival and vitality.

There is not a lot of cactus-specific information on this topic. Most knowledge is based around the commercial production of food, flower and ornamental plants.

I believe that cacti follow the general schema, and methods used by commercial growers. The biggest conflict I found was that a callus should NOT be allowed to form and if formed it will impede root production. This is counter to the commonly held practice of allowing cacti to callus over before attempting to root. I’m not sure what to do with this information; I think I’ll continue to let wounds callus over before putting them in soil at higher than normal humidity.

First the basics:
When you attempt o grow roots on a plant (with existing roots or otherwise), the natural process is that the plant will transport chemicals called auxins (created in the meristem(s) and/or leaves) to the basal part of the plant. When the concentration of auxins reaches the boundary level appropriate for the plant, the cells re-program themselves to be root cells.

Natural auxin production in plant cuttings is usually not sufficient (generally speaking, not necessarily cacti/succulents) to form good roots. Some cuttings may have delayed rooting, sparse roots or may not form any roots.

Where nature fails, science fills the gap! Auxins were “discovered” in the mid-1930’s and much research was done to determine which compounds and conditions worked best.

The two primary chemicals now used to promote root growth in plants are; IBA – Indole Butyric Acid, and NAA – Napthalene Acetic Acid. IBA is more common in commercial rooting compounds. It has nearly the same effectiveness as NAA, but NAA can actually INHIBIT root formation in too high of concentrations.

These chemicals do more than act on the basal part of the plant. They actually suppress shoot (upper plant) growth. The balancing act is to provide enough chemical to stimulate adequate root growth before the shoot growth becomes dominant again.

Commercially available rooting compounds include IBA, NAA or both. They are generally produced either as dry powder or liquid solutions. Some manufacturers now include additional minerals and chemicals in their compounds that they say support root formation and growth.

One phenomenon that I noticed was that the hydroponic/marijuana industry has spawned a number of amusingly named products which may or may not work. When selecting a rooting compound if you don’t know the concentration of either IBA or NAA you don’t know enough about the product to make a buying decision. Any reputable product will include the specific concentration. Assertions, no matter how earnest, that the product will make your plants feel “groovy” are no substitute for knowing what you're buying.

There are several ways to apply rooting hormone:
• Dry Dip (dip only the basal, or butt end into powder to create a uniform coating)
• Gel (dip only basal end; the coating is thicker than powder and less likely to be disturbed when planting)
• Wet Dip (the basal end or the entire cutting can be dipped in a wet solution; in some cases, the cutting may be soaked for a number of hours.)

Wet Dips may be either water based or water and alcohol-based. Alcohol cuts down on pathogen transmission but can burn some plants. I’ve used alcohol-based wet dips on cacti with no ill effect.
• Spray (sprayed onto the cutting after planting in its rooting media so that it runs down the stem to the basal end and/or is absorbed by the leaves and stems.

Once you select a rooting compound (which usually determines application method) all you have to do is determine the concentration of compound to apply. The concentration of dry powders is determined by the manufacturer and can’t be altered. Wet dips can be mixed to your specific concentration specifications so they are very flexible if you are going to be experimenting with different concentrations.

I like using the wet dip method because the product wets the roots which I then dip in potting mix to get it well adhered to the roots. I tried a gel product recently and it worked fine on rootless or nearly rootless plants, but anything with roots turned into a big blob of gel with roots in it. One person I spoke to said that the best application method for cacti should be dry dip, but I didn’t press for details.

But whether you use dry, wet or gel, too low a concentration of auxins will fail to produce roots and too high a concentration can potentially inhibit root growth. Too high a concentration is more of an issue with NAA, IBA does not have the same issue.

The way most people figure out the appropriate concentration is to consult one of the many tables provided by rooting compound manufacturers, find their plant, and use the recommended concentration. The other way is to experiment, doing carefully controlled tests to determine the optimal concentration. Unfortunately the ONLY cactus I found listed was “Prickly Pear”, and option 2 sounds like no fun!

Did I mention that the appropriate concentration for a given plant is also affected by the time of year, type of cutting, humidity, temperature (soil AND air), rooting media, photoperiod, health/condition of the plant, etc, etc… Randomness is looking more attractive right about now.

Of all those conditions humidity and soil temperature seem to have the most significant impact and are therefore the attributes you should try to manage. This is where I think the treatment of cacti will differ from other plants. The humidity recommendations I saw essentially said to mist the heck out of cuttings. Commercial growers have systems set up to mist plants every few minutes.

I think rooting cacti need more humidity than normal, but not sopping wet 24x7. I place the plants/cuttings in a 1020 tray with a loose fitting humidity dome. I spray with water every day or so and bottom water every 4 days or so. This is a light watering, you want to get the water molecules floating up, tempting the roots from below, urging them to come on down.

I hadn’t really considered/managed temperature before, but my research turned up some interesting info. One caution I saw consistently was to avoid large discrepancies between leaf and soil temperature. Temperature influences the speed at which a plant produces roots. Higher temperature produces faster effect. Recommendations seem to indicate soil temperature between 65-70F. Temperatures above 70F can potentially accelerate fungus and bacterial. High temperature of the ambient air will stimulate the growth of shoots at the expense of roots. The recommendation is to keep the air temperature lower than the soil temperature. Easier said than done, in my opinion!

I’m using bottom heat from seedling mats which is probably the only way you’ll be able to maintain soil temperatures higher than the ambient air temperature. If your ambient temperature is higher than 70F you might not get the results you expect.

One other important attribute you should try to manage is photoperiod, the length of time the plant receives light. Rooting plants are not doing a lot of photosynthesis, so they don’t need bright light, but they should have it for a long period each day. Recommendations range from 14-16 hours of light per day.

One website to start with is:http://rooting-hormones.com. It’s a manufacturer site but it gives some good basic info and there are links from there.

Another tip I saw during my research was to NOT use a metal bowl for wet dips. Unfortunately, I’ve been using a stainless steel bowl exclusively for the past few years. Perhaps that explains some of my previous results. I don’t know why but perhaps someone more chemically savvy might know.

[peterb]

Are auxins toxic and able to be absorbed through the skin? I seem to remember reading some fairly extensive warnings on this.

I've never tried rooting or antifungal compounds. Columnar cacti (broadly speaking) seem to root very well given enough time and globular cacti never seem to root, hardly anyway, especially not the tubercled kind, even with rooting compound.

What's your experience with globular plants Tim?

peterb

[DWDogwood]

Very interesting read. Any updated thoughts or experiences?

[cheesoid]

As far as metal bowls go, all I can think of is maybe something in the rooting mix causes an ion exchange with some metals(like acid in a battery), which could produce undesirable salts, or simply render the rooting chemical useless if it's involved in the reaction.

[amanzed]

One other issue about rooting preparations... I know my powders (RooTone et al) are rather old, and I've read that the hormone (auxin) portion is fairly reactive and degrades quickly after opening, whereas the the fungicide portion is more durable.

So when I use old rooting powder, essentially I'm simply applying a bit of powdered fungicide. That is usually fine -- so many of our cacti and succulents do a pretty good job of generating roots from nodes and pluripotent callus (scar) tissue, without the help of growth factors. So for casual propagation or rooting, it tends to work okay.

But for less willing plants... I'd love to know how to optimize this situation for more touchy (or valuable) subjects, as I gradually build my skills in plant culture and propagation.

[Arjen]

peter, if you've never tried rooting powder how can you know if globular cacti root?
if what you say is true that would mean that, for example, degrafting a lot of grafts would mean certain death.

in my experience they do root, however they take time and care. a little sprayed water now and then helps a lot!

[promethean_spark]

I broke a 2.5cm offset off a Copiapoa hypogea, set it in a small pot with media in a shady area of the GH and it grew roots in about a month - no hormones needed. IME, all faster growing cacti root readily, the only problems are in ones that grow so slowly their metabolism can't produce roots faster than they lose water (due to not having roots). Water loss can be reduced with humidity (though that risks rot) and a larger cutting will have greater reserves to survive long enough for roots to form.

Cacti transpire through their skin at night when moisture losses are minimized, so if you want to spray them and have it do any good, it's probably best to spray the body when it's dark.

[TimN]

I agree, PS!

I've been trimming the roots off of some Astro. myriostigma Onzukas, similar to what Hanazono has described in the past (cutting off the tap root.)

I just stuck them in straight Turface and within 6 weeks they had a nice knot of roots. I transplanted them into normal potting mix at that point.

I think there are appropriate situations to use rooting compound, I just can't tell you what those situations are. From my random experimentation, I can't honestly say using it made any obvious improvement. I don't think I killed any (many) plants with it, though.

[Arjen]

I have the same experience, so far it has made no difference if I use rooting powder

when I spray I never spray the plant body, I spray lightly above the plants just to slightly increase humidity

[jessr]

I have only ever tried rooting powder (RooTone I think) but I know I have killed christmas cactus cuttings with using it and had the ones without powder grow roots. Don't know if it was too much or the christmas cactus just don't like it or what but I have stopped using it.

[iann]

I read an article today that recommended using rooting powder on Fuchsia cuttings. Not that's what I call a waste of good hormones, because those things have roots before you've got them back to the potting shed I've never used rooting powder on cacti. Sometimes they root, sometimes not, so I can't claim 100% success without the hormones although I suspect most of the failures were just dead with or without hormonal help.

Cacti transpire through their skin at night when moisture losses are minimized, so if you want to spray them and have it do any good, it's probably best to spray the body when it's dark.

A tricky decision. Are you spraying expecting the cactus to absorb water through its skin? I suspect that won't get you very far day or night. Are you spraying to encourage roots? Shouldn't make much difference day or night, although it will stay wet for longer at night (which might be bad!). Are you spraying to raise the humidity? More important to do this during the day, because the humidity is already high at night (maybe not in Arizona!). Despite what you might think cacti lose approximately as much water through closed stomata in the heat of the day as they do through open stomata at night, just tens or hundreds of times less than they would lose with open stomata during the day.

[promethean_spark]

I spray the body hoping some water will soak in. I don't know if any actually gets absorbed, but the pores on the plant's skin close for the day so it seems logical that if it is going to soak up some moisture, night would be the best time.

Don't some copiapoas, ect, get more moisture from morning dew on their bodies than through their roots?

I suppose one could weigh an unrooted cutting with an accurate scale and compare it's before/after weight on nights where it's sprayed and nights where it's not to see if it gains weight from the spraying.

[iann]

There is a popular perception that foliar absorption of water, and anything dissolved in it, is pretty much universal. However, research shows that it is the exception rather than the rule, or at least too small to be interesting in most cases. I'm not aware of any research showing it in cacti, but then they have little or no "foliage" There have been limited reports that water can be taken up directly through some cactus spines, but also others that the spines are simply collecting and directing the water. Useful levels of foliar water absorption has been shown in a number of Crassula species and also a small number of Tillandsias. The use of surfactants dramatically increases uptake of liquids through leaf surfaces in many species, but this might be via a different mechanism.

One thing that seems universal is that liquid uptake does not primarily take place through the stomata. The stomata in any case do do not connect into the vascular system for liquids, but into different structures used for exchanging gases.

Dew formation on Copiapoas is generally to the point of runoff. There is also dew formation on the ground itself, and this could be a far greater source of liquid than dew on the plant itself. I've experimented with spraying and frequent light watering as a cultivation technique for Copiapoas and found it a complete failure, although that could be down to my climate. Now I just water them like any other cactus.

In mesembs in the African fogbelt, and also in cultivation where frequent spraying is a common practice, the water still seems to be taken up mostly by the roots. You can spray a rootless Lithops all you want and it just doesn't behave like one with roots that gets the same amount of spray. Lithops may be a bad example, but the fogbelt species Fenestraria has a massive root system that can only be useful for collecting ground condensation.

[TimN]

About the only thing I can remember reading was that by having a more humid environment near the stomata, that some of the escaping water vapor could bounce off local water vapor and back into the stoma. Sounded like wishful thinking to me!

My understanding of the South American fog cactus was that the hair/spines/fibers condensed the mist and directed it to the roots.

I can't imagine a cactus taking water in through a spine/fiber/hair. Mature spines are all dead cells with no structures to transport anything.

[iann]

About the only thing I can remember reading was that by having a more humid environment near the stomata, that some of the escaping water vapor could bounce off local water vapor and back into the stoma. Sounded like wishful thinking to me!

Sounds weird, but effectively that is what happens. In the same way that water evaporates more slowly when the air is humid, because the water molecules "bounce back" from the water molecules already in the air. In practice they don't have to bounce anywhere, there is a continuous exchange of water molecules to and from the surface of any liquid water. The less water there is in the air, the more the balance tips towards water leaving and not coming back. When the air is saturated, relative humidity 100%, then just as much water comes back into liquid as leaves it. In fact this is the definition of 100% relative humidity.

In fact this is crucial to the survival of cacti and many other succulents. Their whole metabolism has been modified so that they only have to open the stomata at night. During the day, temperatures are high and humidity is low so a huge amount of water is evaporated if the stomata are open. At night, temperatures are cooler and the humidity rises, frequently towards 100% even in desert environments, so water evaporation drops to very low levels.