Root Comparison Part 2: Evaluating the Quality of Hemp Clone Root Structures

April 11, 2020
Category: Hemp

In part one of our root comparison study, we compared the root development of seedlings vs. clones to test the assertion that seedling root systems are superior to hemp clone root systems. If you haven’t read that post, be sure to check it out!

Hemp Clone Root Comparison seedlings vs clones

In this second phase of testing, we wanted to compare the effects of loose-fill soil vs. Ellepot production on the development of hemp clone roots, especially as it relates to root spiraling. Loose-fill production has been in use for centuries (including in our own greenhouse) and is in no way bad. However, our experience with Ellepots in ornamental production told us that they could be vastly superior with hemp clones as well, so we put them to a head-to-head test.

After showing you the results of this trial, we’ll share some tips on how to evaluate the health of your roots when they arrive so you can be sure you received quality starter plants.

The Parameters

We planted identical Wife clones in the same kind of soil on the same day: half were loose-fill and half were Ellepots.

Observations include the direction of root growth, the thickness of primary root structures, and the depth of growth of thicker roots.

The Baseline

Normal production time for rooting a clone is 18-28 days, depending on the length of day, sunlight, heat, etc. We chose to use 24-day clones (winter production) as our control for the experiment.

Hemp starter plants in Ellepots
Ellepot plugs at 24 days
Hemp starter plants in loose fill
Loose-fill plugs at 24 days

All of these hemp clone starters have been grown for the correct amount of time and are ready to be transplanted.

The Ellepot starter plugs show white roots that are well-formed with a vertical growth pattern.

The loose-fill starter plugs also have a healthy white color, but because they’ve filled the space they’ve begun to grow in various directions, indicating that there would be future problems if they were left in this size container.

24-Day Root Development: A Closer Look

We selected a sampling of each category and washed the soil off as delicately as possible in order to maintain the developing hemp clone root structures. We wanted a closer look at what was happening beneath the soil.

Ellepot vs loosefill hemp clone root comparison plug
Left: Ellepot, Right: Loose-fill
hemp clone root comparison plug wash
We washed the roots clean to get a closer look at growth patterns.
Ellepot vs loosefill hemp clone root comparison exposed
The Ellepot (left) has consistent downward growth patterns with air pruning of roots.
The loose-fill plug (right) shows some spiraling of roots near the surface.

The Ellepot hemp clone roots show a more consistent growth direction, thicker roots in general, and a healthier overall appearance.

The loose-fill hemp clone roots show some spiraling tendencies near the surface with an overall thinner root structure.

The Science of Air Pruning

The air pruning of roots is not new science. It happens naturally when roots are exposed to dry air. The roots are burned off, causing the plant to continually produce new, healthy roots. This is hugely important to propagators because it increases our ability to deliver high-quality starter plants to hemp farmers.

When roots are not exposed to the air, they grow around the container in a circular pattern and could spiral, kink, and eventually become strangled. Spiraling root systems will negatively affect a plant’s natural ability to anchor itself to the ground or achieve maximum nutrient uptake.

60-Day Root Development: First Impressions

A side note here: sixty days is way too long for your clones to be sitting on a table. Suppliers don’t do customers any favors by selling them old, stressed plants. Ideally, you’d want a clone whose roots are still developing rapidly rather than a one whose roots are already competing with each other for space to grow.

However, we let these hemp clones continue to grow in order to see how our Ellepot production would compare to loose-fill regarding the shelf life of viable material.

Ellepot vs loosefill hemp clone root comparison overgrown
60-day roots: Ellepots (left) vs. loose-fill (right)

You can really see the air pruning on display here. The Ellepots have continued to develop thick vertical roots and look to be far superior to their loose-fill counterparts.

Ellepot vs loosefill hemp clone root comparison overgrown closeup

The bottom of the loose-fill plugs are thick and starting to get hard, and from a grower’s standpoint that tells me that they are beginning to be root-bound and could present problems in the field if I don’t get them transplanted ASAP.

The tips of the Ellepot roots, however, still appear healthy from the natural air-pruning and look like they’re ready to grow deeper.

60-Day Root Development: A Closer Look

cross section of hemp clone root development
We cut two plugs in half to see what a cross-section of the root structures would look like. Ellepot (left) vs. loose-fill (right)
hemp clone root comparison 60 day
We gently washed two other clones to compare their root structures without soil.
Ellepot (left) vs. loose-fill (right)

The longer the clones sat on the bench, the more obvious the superiority of Ellepot production became. While the loose fill is starting to display some very concerning spiraling, Ellepot root systems continue to look very healthy with continuous vertical growth and thicker primary roots.

Looking at this from decades of growing experience, the contrast is directly tied back to how the roots behave when they run out of space. The loose-fill plugs run out of room when they hit the tray, so they begin growing in circles in search of space. The Ellepot roots stop growing in length when they hit air, but the root continues to develop and thicken in order to compensate, creating a visibly stronger root system.

How to Evaluate Your New Hemp Clone Root Systems

When clones arrive, most people look at height and color to judge the health of their plants. While those things are indeed indicators of plant health, there are two very important additional tests that professional growers do to check their plants. The first is to check for pests (which is a whole other blog post), and the second is to inspect the roots.

When analyzing root development, you have to recognize that there is a spectrum from underdeveloped roots all the way to root-bound systems, and in the middle of that spectrum is a sweet spot. There’s no hard-and-fast scale by which you can determine whether or not a plant is root-bound, but there are indicators that can tell you how far down the spectrum a particular plant has gone.

Root ball comparison on hemp clone root
From underdeveloped to extremely root-bound: a spectrum of growth
  • Underdeveloped Roots
    • Few or no visible roots when the plant is removed from the tray
    • Main stem separates from the roots even when dislodging the plug from the bottom
    • Root ball falls apart or drops dirt
    • Very thin main roots do not allow for adequate nutrient absorption
  • Sweet Spot Roots
    • Bright white, visible roots
    • Roots that don’t break away from the main stem easily
    • Visible soil that indicates that roots still have space to grow
    • Root ball stays together as a plug, but there’s some give when it’s squeezed
  • Pot-Bound Roots
    • Less visible soil (roots have encased the dirt)
    • Spiraling
    • Brown roots that are hard to the touch
    • Bottom edge of the plug encircled by darkened roots
  • Extremely Pot-Bound Roots
    • No soil visible (roots have completely encased the dirt)
    • When you squeeze the root ball, it’s firm and doesn’t give at all
    • Roots are thick and brown
    • Possibly even so much growth that plugs are difficult to remove from the tray.


Whether your supplier uses loose-fill soil, Ellepots, or another soilless media, the value you get is directly tied to root structure. Even if you have good genetics and no pests, an overgrown clone is going to give you trouble. Loose-fill and other soilless media can give you good results, but Ellepots seem to create clear advantages for both suppliers and customers.

Based on this trial, we’re convinced that Ellepots will help us deliver a consistent product to each customer. As a result, we are in the process of converting all future hemp production to Ellepot trays and making our pre-filled Ellepot trays (made on-site) available to customers who wish to root their own plants.

Stay tuned for updates on our field trial root comparison later this summer!

All photos ©Rachel Donahue, North Carolina Farms, 2020