A batch of clones in rockwool

A lot of people have trouble with clones in rockwool until they have done a few batches. Here's a photoessay on a batch of clones as they are done around here.

One of the biggest problems with rockwool cubes is that they can hold a LOT of water. If cubes are too wet, rooting will be slow or stem rot may set in. Think damp, never wet or saturated. A dry 40mm cube weighs 5g. A properly "damp" cube weighs 25-30g. Heavier than that is too wet. Remove water from overwet cubes by shaking excess out into a bucket with a snap of the wrist. A salad spinner is great for draining cubes after pre-soaking, without giving yourself 'tennis elbow.' Rockwool cubes must never be squeezed- removes airspaces.

Since I grow SoG style, I cut very tall clones. Taller clones become taller plants faster- important in SoG as no vegging time is given to clones before they are flowered. As soon as they have a good set of roots, they go in to the flowering area.

My clones are too tall to fit in a humidome, but humidomes usually keep things TOO humid anyway, especially when using rockwool cubes on a heatmat.

Clones do best in a controlled environment, so I built a clonebox with 3x twin 18W fluoros (on 24/7), a fixed-temp (30C) heat mat and a thermostatically controlled exhaust fan. The ballasts on the fluoro lights put a fair amount of heat into the box air. When the temp comes up to 26.5C, the fan kicks on.

So, here we go!

First, sterilise all plant contact surfaces (trays, inside of clonebox) with a 10% bleach in warm water solution. 1-2 drops of dishwashing soap helps make the cleaning solution "wetter," assuring every little nook and cranny is germ-free. Rinse and allow to dry. Don't forget to wash your hands thoroughly with the same solution- use a fingernail brush.


These mother plants are about 6 weeks old. They've donated about 3 sets of cuttings and will be replaced with one of their 'kids' soon.

Note that these are only two of my mothers. I keep 8-10 mothers to support donation of 30 cuttings every 15 days. Mothers are vegged under a 400 HPS (soon to be a metal halide).


Rockwool cubes are first rinsed well under running tap water then pre-soaked in a bucket of pH5.0 water for 24 hours. All the pre-soak water is removed with a salad spinner.

Immediately before plugging in cuttings, cubes are each given about 25ml of a clone watering solution made from:

* 10L tapwater
* 30ml H2O2 (50% horticutural grade)
* 5ml each Canna Vega "A" and "B" nutrient, should yield a (weak) 400ppm solution
* pH corrected to 5.3-5.8 (correct pH after adding everything else)

The nutrient is not entirely necessary- a plant without roots can't assimilate nutrients, only water- but nutes in the clone watering solution assures nutes are available to the plant as soon as it has formed root nodes. This gets nutes to the plant a day or two before you actually see the roots out of the bottoms of the cubes. Well developed mothers in good condition will have a couple of weeks worth of nutes stored in the leaves- and so will the clones you take from them.


A well developed mother plant about 4 weeks old. Has donated about two passes of cuttings.


Sterilise the scalpel blade by dipping in methylated spirit (aka denatured alcohol) before and between making cuts


I cut BIG clones. Stem length is about 9".

Cut the biggest diameter stems you can get for clones. This is how they look when just cut off the mother. Make the stem cut at an angle, about 45 degrees.


Cut off all the branching until you have something like this.


Split the end of the stem. Disrupted cells on the stem more easily become root nodes.


Gently scrape the last 25mm (1") of the stem in a few places with the back of the scalpel blade.


Dip the stem in rooting powder. Gently knock off any excess; only a dusting is needed.

Powders work better than gels because they form a paste which stays put through several waterings.

Gels can support pathogen growth in between batches. If you use gels, put a few ml in a small container and dip stems into that gel- not in the main container. Discard any excess. Even opening the gel container will admit a few pathogens. Once opened, keep gels in the refrigerator.


Plug the stem into the cube, using care not to poke through the bottom of the cube.

It is important that the rockwool fits tightly around the stem. Some cubes are not very dense in some parts of the cube. Test the density of the rockwool by touch and plug the stem in the densest part of the material. Some cubes collapse when you try to plug a stem in them. Discard cubes like this. The air gap between the stem and cube will prevent proper rooting.

Clone #1 done!


Big clones work better in Sea of Green. There's no veg time given to clones in SoG before flowering. Bigger clones make bigger budstalks. As you see, these are about 9" tall.


Now, let's prune back the mothers.

Some stems are too small to make cuttings with on this pass. We'll take cuttings from these stems when they have developed more in about 2 weeks.

Snip off the growing tip to force growth to divide. Leave the leaves and the following nodes- these sites will develop into cloneable branches on the next pass of cuts in 2 weeks.


Mother plant pruning detail. Growing tips gone but the next nodes down are not disturbed.


Mother plant pruned and ready to go back in & veg for 2 weeks until the next batch of cuttings is needed. "Before" pic repeated here for comparison.


A freshly done batch of clones in the clonebox.


Roots pop on day 6-7.


Roots on day 8.


21/30 strikes on day 10.


And here we are on day 10. No yellow leaves! Yellowing leaves are a sign of excessively high air temp or overwatering. Cubes in the left-hand tray have not set root just yet. I only need 20-21 clones per flowering batch. Extras become mother plants- or compost!



Thick stemmed cuttings outperform thinner ones. The stack on the left all have stems about 4mm or less. The stack on the right all are over 5.5mm.


By Day 12, the roots are well developed enough that this lot can go in to flower.

The clonebox conditions and getting the watering right are EVERYTHING. Quick rooting with the plants in best shape is dependent upon several things; I consider a heatmat to be an essential. Thermostatic control of air temp makes striking time reliably 6-7 days, every time.

Now- send in the clones!

 

Thanks much willydog & rollinfatty.

I wanted to post the info that I was needing badly some years ago.

Took me a while to get it right when first working with rockwool cubes. Like everyone, I overwatered my first few batches and made them really slow (like 3 weeks...).

I think I have it down pat now, but as soon as I say that, clone-eating fucteria from the planet Gorgonzola will invade earth and teach me a thing or two.

 

One thing I should mention is that the watering interval for different growers will invariably be different depending upon their particular clonebox conditions.

It has been a little cool here recently, so I just added a small fan to my clonebox to circulate warm air coming off the fluoro ballasts. The fan is a cheapo 100mm desktop fan, fixed in place above the fluoros, blowing air upward, away from the plants. However, the air still bounces off the interior top of the clonebox and makes its way down to the clones.

This fan has sped up the evaporation rate from the cubes dramatically. I checked them yesterday morning to find that 4 clones had wilted. Thankfully, they didn't totally collapse and were recoverable.

I normally water clones 1x day by dipping only the bottom 1/3 of the cube into the clone watering solution for 2-3 seconds. I've taken to dunking the whole cube now.

Without the thermostatic exhaust fan control (set to 26.5C), the 30C fixed-temp heatmat and now the circ fan which have combined to make for a high evaporation rate in the clonebox, dunking the cubes fully would quickly cause overwatering symptoms.

When setting up a new clonebox, one should wet some cubes, weigh them and run them (without any clones in them) in the clonebox for a few days until you get a good feel for how fast cubes will dry out in your particular conditions. Ideally, you're looking to have about 1/4-1/3 of the water weight remaining after 24 hours. If things dry out too fast but temps are still right, you may have to water more lightly but twice a day.

Keep in mind that once clones have developed a bunch of roots, they will suck up much more water than before they had set root. Check them at least a couple times a day.

If you must 'idle' rooted clones until you have space available for them, you may wish to shut off the heat mat and turn the air thermostat down a few degrees to slow them down a little. Clones work best when 'fresh,' though, and should be planted into growing media after several taproots are showing but before roots are overdeveloped.

 

thanks, waddo.

Watering is where I stuffed it up early on.

Glad this seems useful.

 

You'll note a significant deviation from standard cloning advice in my method.

While many old grow guides recommend taking tiny cuttings with few leaves or even cutting leaf blades in half, misting often and whatnot, high humidity isn't necessary if the cutting is able to pick up sufficient water via the stem. High humidity can more often than not induce fungal probs like powdery mildew on leaves.

If the rooting medium has been kept too wet, there's a possibility that stem rot may set in, blocking water uptake and causing wilt. This is often mistaken for wilt caused by low humidity. New growers often unfortunately compound an overwatering condition with an overhumid condition... and it all comes to tears.

If the rooting medium is properly just damp and slightly warmed, rooting is quick and reliable- without misting or humidomes.

 

I couldn't tell you! They're plain ol' 18W, 24"(?) common fluoros. My light meter laughs at them.

Clones need not be pounded with light. You just need to convince them it is daytime for 18-24 hours a day. Too much light isn't a good thing when a plant either has no or an underdeveloped root system.

I do run clones under 24hr light, but they are working pretty hard keeping up water intake in their first 24 hours after cutting, so I usually turn the lights off for their first 6 hours in the box.

 

From your description, you're probably right. Whatever the medium, it must be damp and slightly warm, but never saturated or wet.

A sterile medium like rockwool, sterile plant contact surfaces (esp your hands & tools!) and sterile watering solutions put you miles ahead.

Thanks for the compliment.

Cloning isn't hard. Getting the conditions right is the tricky part. If you build a clonebox which presents consistent conditions, you'll get consistent results.

The little battery operated thermostat I added to the clonebox a while ago has made worlds of difference. Wasn't really needed in the last place the box lived but it's a bit cooler in its new location, which made for inconsistent rooting speed. The tstat keeps it bang on ideal temp at all times; you can set your watch by the rooting speed these days. Day 6, I'll see the first taproots poking out, every time.

 

All sounds great That's a lot of CFL just for cuttings, tho.

This is the thermostat I'm using:



Got it here, don't know where you can get it outside Australia. Runs on 2x AAA batts, don't know how long they last but it's been running on a single pair of Duracells for about 2 mos now.

The thermostat only controls my clonebox exhaust fan. The heatmat has its own internal thermostat and runs at a fixed 30C surface temp- it is plugged in 24/7/365 and has been for several years. This heatmat is moulded in silicone rubber- and is much more durable than any other I have ever found. Wasn't cheap.

Glad my notes are of some use to you.

My clonebox varies from about 30-60%RH, never any wilt, certainly nothing induced by low humidity. Would invite any cloner to try a clonebox instead of a humidome. If you can keep the air temps fairly consistent and the watering right, cloning will be quick & reliable.

 

It's been cool here recently (ambient around the clonebox is 10-13C @ 70-80%RH), so I needed to work out a way to warm up the clonebox a little. I added a cheapo 150mm desktop circ fan to the clonebox as shown.



Points upward, away from the plants.



Fixed to the wall by running screws straight through the fan's plastic base. It's SO much fun to drive drywall screws through a brand new piece of electrical equipment.

Moves the air around enough to circulate a little heat from the fluoro ballasts, enough to trigger the thermostat often, holding temps +/- 0.5C from the 26C setpoint according to the peak-mem thermo-hygrometer.

 

Dunno, maybe the 125W CFL might be better used for vegging.

I think I paid $AUD40.00 for the tstat. If you live o'seas from Aus, you might pay $5-10 to ship it.

Sorry, did you mean 60-64F @ 5% RH?

Too cool. My clonebox thermostat is set for 26C (78.8F).

Agreed. The cuttings came off a mature mother plant which was quite accustomed to good air motion and ability to transpire water due to reasonable RH (bout 50-60% in my mother area). A humidome would slow or stop transpiration, not necessary if the water can come up the stem. Encouraging water transpiration through the plant would reasonably encourage the formation of roots, too.

 

74-78 @ 60-65% is fine