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Root Comparison: Seedlings vs Clones


March 10, 2020
Category: Hemp

There’s an ongoing debate about which is superior: hemp clones or hemp seedlings. You’ll hear arguments that go something like this: clones are more uniform in the field, more true to type, and 100% female, but seeds are more easily stored, free from pests from the beginning, and–this is the big one–produce a taproot.

We decided to put that last one to the test. How would seedlings and clones compare in a side-by-side root test?


Botany 101

First, let’s define our terms so we’re all on the same page. The following definitions are all taken from this article from Washington State University:

Roots have three primary functions: 1) to anchor plants to the ground so they can endure strong winds and flooding rains; 2) to absorb water and dissolved minerals from the soil to feed plant leaves and fruit; and 3) to store reserves for the plant, an especially important asset for winter survival in perennials.

There are two basic types of root systems: fibrous and taproots.

Fibrous root systems have a mass of similarly-sized roots which tend to concentrate in the top foot or so of soil. A significant number of lateral or sinker roots may grow downward from these roots to provide an effective absorption system and act like a tripod to secure the stem/trunk and foliage.

Taproots consist of one or more main roots with smaller side roots. Taproots grow straight down, rather than spreading along the surface. These roots can become woody, providing strong anchors for the plants and trees that have them. Taproots are also an important adaptation for searching for water.

Both fibrous and taproot systems have long root hairs which occur in great numbers just behind the tip of the growing roots. These root hairs vastly increase the surface area available for absorption of water and nutrients. They are extremely delicate and easily damaged.”

hemp break at stem
High winds can cause severe damage to hemp crops in the field when heavy colas overstress the plant structure causing breakage–typically at the stem and not the roots–like the clones pictured above.

One of these is supposed to have a taproot and the other a fibrous root system.
Can you tell which is which?

Industrial hemp is in a rather interesting category of plant: like tomatoes, a seed will form a taproot, but a clone will form a fibrous root system. The argument from some is that the taproot system is superior to the fibrous root system, so we decided to put our clones to the test in side-by-side trials against hemp seed from the same genetics (in this case, BaOx) to see what we could learn.


Hemp Root Test Parameters for Phase One

The first test we decided to perform is a six-week indoor grow: seedlings and clones were transplanted into gallon pots on the same day using a loose soil potting mix. (We plan to repeat this type of test in the field later this summer, so please don’t write me hate mail about using potting mix). We decided to test the following parameters at the end of this six-week grow:

  • Root length
  • Diameter
  • Weight
  • Number of roots from the main stem
  • Stem thickness
  • Appearance of root spiraling
Clones grown pot tight for 6 weeks
We transplanted the hemp seedlings and the hemp clones on the same day and grew them both pot-tight for six weeks.

It’s important to understand that this test is one-dimensional on purpose. We are currently doing other tests on Ellepots vs. loose soil production, and later this summer we’ll be doing further tests in the field. This first test is just that–phase one of a series–but the results are fascinating, so we wanted to go ahead and share them with you.


Preliminary Root Growth Observations

Hemp Seedling vs Hemp Clone 1
Can you tell which of these is the seedling and which is the clone?

The first thing we noticed is that there’s no visible difference in the direction of the root growth between hemp seedlings or clones. I’ve heard it argued that the taproot won’t spiral–it will grow straight down while fibrous roots spiral. In the above image, both root systems have maximized the space available to them and begun to spiral. I’ve long hypothesized that if seedlings or clones either one are left in the plug tray too long, the roots will inevitably spiral and produce unhealthy root systems. Root direction, then, is heavily influenced by available space and available nutrients. (To satisfy your curiosity regarding the photo above, the seedling is on the left and the clone is on the right.)

Takeaways:

  • Always transplant your starters on time–and don’t buy overgrown seedlings or clones.
  • In irrigation, make sure to water deeply at slower intervals instead of watering shallow and often. This will promote deeper root penetration.

Digging Deeper

The next step was to try to soften the soil and loosen as much as possible without disturbing the structure of the root system. (Plainly stated, we dunked them in a bucket and gently hosed them down.)

Seedling vs clone root ball close up
Note the structure of the root growth (L seedling, R clone)

Key Observations:

  • At this point there appears to be a main root present on the seedling.
  • The root volume on the hemp clone is so great, we can’t really see the root structure just yet.
  • There does seem to be some spiraling on the clone close to the surface, but it’s difficult to tell because the root density has completely filled the pot.

Hemp Roots Exposed

Hemp seedling vs hemp clone 3
With all of the dirt washed away, we can get a better look at root structures.

With the roots clear of dirt, we began to get a better picture. Both seedlings and clones had bright white roots and appeared to be healthy. While the visual contrast seemed to tell a story all its own, we wanted countable data to compare, so we took measurements of everything we could think of.

The root systems of the hemp seedlings had an average of 16 roots extending from the stem. Only four or five of these seem to be primary roots at this stage of growth. Seedlings 2 and 4 had some visible spiraling at the very base of the stem.

Hemp seedling root systems
Root structures of the hemp seedlings

The root systems of the hemp clones had an average of 37 roots extending from the stem, with five to eight larger roots each. Clone 1 had some early spiraling of two roots. While clones 3 and 4 have a downward growth pattern, they seem to have a slight rotation as well.

Hemp clone root systems
Root structures of the hemp clones

Seedling vs Clone Root Density

When we measured root length, the seedlings averaged 17 inches in length, with the longest root measuring 18.25 inches. The clones averaged 15.68 inches long, with the longest root measuring 19 inches.

The average root diameter for seedlings was 112 microns, and the average for clones was 74.75 microns. The average stem thickness for seedlings was 325.5 microns, and for clones 411 microns.

Max Root LengthMax Root DiameterStem Thickness
at Soil Level
Seedling 116.25″110 μm 346 μm
Seedling 218.25″120 μm 378 μm
Seedling 315.75″93 μm 265 μm
Seedling 417.75″125 μm 313 μm
Clone 115.50″72 μm 395 μm
Clone 214.50″72 μm 386 μm
Clone 319.00″80 μm 470 μm
Clone 413.75″75 μm 393 μm

Now is a good point to remember the three purposes of roots listed above: to anchor plants, to absorb water, and to store reserves for the plant.

For an accurate assessment of anchorage, we’re going to have to do more tests in the field this summer. The questions will be:

  1. How deep do the different root systems penetrate?
  2. What kind of force would it take to uproot each type of plant?

When it comes to water absorption and nutrient retention, the fibrous root system appears to have much more surface area, and therefore more potential for greater plant health.

As it stands now, based on general appearance, clone fibrous root systems give the plant sufficiently stable anchorage, but with the added benefit of increased water absorption from the soil, and a larger area for nutrient retention between waterings than their seedling counterparts.


Day 2: Dry Hemp Root Tests

Hemp roots drying
We dried the roots overnight so we could weigh them and compare

After taking our initial measurements, we dried the roots overnight then weighed them to get an idea of overall root density. The average dry weight for seedlings was 2.5 g, and the average dry weight for clones was 5 g.

Next we trimmed off all the excess fibrous roots and tried to get an idea of how many of those roots connected directly to the main stem as an indicator of the support structure.

Cutting away excess root mass
We cut away smaller roots so we could get a better look at where roots connected to stems.
Dry WeightNumber of Roots from Main Stem
Seedling 12 g21
Seedling 24 g18
Seedling 31 g8
Seedling 43 g18
Clone 16 g36
Clone 24 g46
Clone 35 g36
Clone 45 g32
Hemp root seedling vs clone pared down
With all of the excess stripped away, we got a fascinating close-up look at the structures where roots connect to stems.

Conclusion

There’s no doubt that the root structures between hemp plants grown from seeds and cuttings are different, but this preliminary test is just not conclusive enough to say that a seedling’s root system is superior over that of clones. It’s a test that warrants further tests. As a clone producer, though, I’ve been impressed by the quality of our root systems, and I am confident in their ability to provide stable anchorage, to absorb large amounts of water, and to retain ample nutrients: in short, to support healthy plants.


More testing is underway on spiraling and different media types. We’re currently testing loose fill production vs Ellepot production at two week intervals of growth. We’ll update you on that test in the coming weeks, but here is a sneak peek: