Cannabis Seedling Conditions and Care

Cannabis Seedling Conditions and Care:

Flower may get all of the glory, but good growers know that the money is made in the veg room.

Whether you are growing from seed, or from a rooted clone, the steps you take during the early growth stages will set you up for success.

Your plant’s root and shoot structure can be shaped for less work during veg, and higher yields at harvest time.
Beneficial microbes can be introduced to form a relationship with your plants and protect them from disease.
Seedling care will prepare your plants for more aggressive grow environments during the veg and flower stages.

Seedlings vs Clones

Cannabis is easy to clone and there are advantages to growing genetically identical plants.
Canopy management is simper when your plants all have the same growth habit, and flower consistency is important for buyers.
There are also drawbacks to growing from clone that outweigh the benefits for many growers.
Clones that have been shared often carry pests and diseases that are hard to eliminate once they are established in your crop.
Live plants are difficult to ship, and most garden centers don’t carry much of a selection in the weed section.
A wide variety of feminized seeds are available to be mailed anywhere in the world, and they are usually disease free when you get them.

The best practice for growers at any scale is to start from seed and pheno hunt.

When you find a special plant, you can keep a healthy mother and clone her forever. The genetics that you choose to grow will have a big impact your success.

Not all strains are suitable for all growing conditions, so do some research before purchase. Seeds should be sourced from a reputable breeder who can provide information about the strains that will work best in your conditions.

Check out the outdoor grow guide for more info on genetic selection.

Rooting Clones

Clones like humidity over 80%, 24-hour photoperiods, and low light conditions to form new roots.

Plastic domes can be used to create a humid environment for your cuttings. High humidity and no airflow create ideal conditions for disease, and clone domes should vented and removed periodically to allow for air exchange.

**Biofungicides** are beneficial microbes that help prevent disease without the use of chemical pesticides.
Peat pucks or root cubes can be inoculated with products containing *Bacillus* or *Trichoderma* prior to seating clones.
These microbes will form a lifelong relationship with your plant to help prevent Damping-off and other diseases.
When clones have started to root, the relative humidity should be gradually reduced to 70%-75%, which is optimal for the early growth stage.
Once clones are acclimated to vegetative growing conditions, they can be transplanted and cared for like seedlings during juvenile growth.

Seedling Growth Conditions

Young plants need to be nurtured to achieve their full potential. Ideal growth conditions for seedlings include 65%-75% relative humidity and temperatures of 70-80 F (22-27C).

You can use an inexpensive digital sensor to log temp and humidity (there is an app for that). If you really want to know how your plant is feeling, use a laser thermometer to take the leaf surface temperature.

Fresh air is required for photosynthesis and smooth airflow through your plants will help to prevent disease. If you are growing in a tent, and your only climate control is an inline fan, a variable speed control will help you manage the climate.

Most indoor climates run too dry for seedlings, and a small humidifier can be a worthwhile investment. Misting seedlings can help with humidity, but liquid water on your plants provides an entry for disease and should be avoided.

For outdoor growers, a small greenhouse will give you a big head start on the season. If you are in a sunny location, all you need is an extraction fan to promote plant health. Light intensity is 30%-50% lower in greenhouses, and plants will usually benefit from supplemental lighting. If power is limited, a small string of incandescent lights will keep your clones from flowering prematurely during the short days of spring.

Seedling Germination

You can help your plants get a healthy start before they germinate by soaking seeds in a .5 to 1% hydrogen peroxide solution.
This will kill pathogens on the outside of the seed, provide oxygen to the embryo, and soften the seed coat for faster germination.
Seeds can be planted directly in large pots, or in the ground, but growing in small pots for a few weeks has several advantages:
Small root balls are easier to water correctly.
Many plants can be grown in a limited footprint.
Plants in small pots are easy to prune and train.

If you are growing a lot of plants, it is easier to sow seeds in small plugs or peat pucks and transplant them to pots when they are well rooted.

Seeds do not need high relative humidity to germinate, so it is best to avoid the plastic domes. Autoflower seeds are not tolerate of root interruption, and should be direct sown in their final location, or transplanted as soon as they are well rooted in a plug.

Seedling Soil Mix

Seedling mixes are made from natural fibers, like peat moss and coco coir, that allow for rapid air and water exchange in the root zone.

Aeration is improved by adding perlite, pumice, or rice hulls to create an environment where roots and microbes will thrive.

Conventional growers will often start seedlings in a sterile mix.
Organic soils contain probiotics that help to feed your plants and protect them from disease.
Compost and worm castings provide available nutrients, and billions of beneficial microbes ready to go to work for your plants.
Fertile organic soils usually contain indigenous mycorrhizae. These fungi are highly beneficial for water and nutrient uptake by roots.
In addition to compost, a variety of soil amendments are used to build fertile potting mixes. These inputs provide essential macro and micronutrients to feed the soil microbes that feed your plants.
Living soil doesn’t ship well, and the best potting soils are usually made from ingredients sourced in your area.

You can also make your own organic mix by following my not-secret-anymore living soil recipe.

A fertile organic seedling mix will support root health and rapid growth. Conventional growers can also benefit from the power of probiotics by using bottled inoculants.

Root Pests

If you start with a suppressive living soil, and pay attention to irrigation, you will probably never have an issue with fungal root diseases.

Insect pests are a different story. Soils provide habitat for many insects at various life stages. Some of these are detritivores that consume organic matter, but others are herbivores that can emerge from your soil to feed on your plants.

Many pests can be killed while they are still in the soil by watering in predatory nematodes at transplant. These microscopic worms will move through your soil consuming fungus gnat and thrip larvae. Predatory nematodes are inexpensive and happy to chill for a few weeks in the fridge, making them a practical biocontrol for small scale growers to use.

If they survive the nematodes, fungus gnats will usually hatch and swarm on the soil surface a week or so after transplant. These pests feed on roots and can spread disease between plants. Swarming gnats can be knocked down with bioinsecticides containing BTI. This naturally occurring soil bacteria is safe for use in organic gardening.

Seedling Growth
When a seed germinates, it first sends a tap root down into the soil.
Once the root is anchored, the stem unfurls, and a pair of simple rounded leaves opens.
These seed leaves are followed by the first true leaf set. The first true leaves are single bladed, serrated, and look like cannabis leaves. As your plant grows, new leaves will continue to form along its stem.
The intersection of each leaf stem with the main branch is a growth node. As the plant develops, small growth shoots will start to form at each node.
Each new shoot is fueled by the leaf that is growing with and will continue to grow and develop a new branch with leaves and flowering sites.
The speed of plant growth will vary based on many factors. Healthy seedlings will often form a couple of nodes per week.

Seedlings need some time to develop before they are sexually mature and ready to flower. Nodes will develop in pairs along the stalk, then begin to alternate as the seedling moves to vegetative growth.

As your plant matures, pre flowers will form at each node allowing identification of male and female plants. Plants will respond to good growing conditions by building leaves of increasing complexity.

After 4 to 6 nodes of growth, plants should be producing small 5 bladed leaf sets that will grow to become large fan leaves as the plant develops.

First Transplant

The seedling stage often begins and ends with a transplant. Clones or seedlings usually spend about two weeks in plugs before they are well rooted and ready to go.

The soil that you are planting into should be moist and fluffy. Properly hydrated soil should clump together, but not leak water when squeezed. Mycorrhizal inoculants can be applied directly to roots at transplant. Living soils usually contain indigenous mycorrhizae and may or may not benefit from inoculation.

Plugs are pressed gently into the soil at the center of each pot, and loose soil added until the plug is covered.
Following transplant, pots are watered so that soil completely fills any air pockets around the root plug.
Adding liquid kelp to your irrigation water will help your plant quickly root into the new medium.
In addition to micronutrients, kelp contains natural plant hormones including cytokinins that help reduce stress and benefit root development.

The best kelp products are cold pressed rather than heat treated to preserve these qualities.

Once plugs have been transplanted, and thoroughly watered in, it is best to let the soil dry out as much as possible before the first irrigation. This dry back will motivate roots to expand through the soil seeking water.

Irrigation Water

Water quality is important. Tap water often contains chlorine or chloramine. These chemicals kill microbial life. Chlorine will off gas if water is left out overnight, but chloramine is more persistent. Rainwater or well water are usually good sources for irrigation water, and don’t need to be PH adjusted in organic growing systems.

Water reservoirs should be shielded from light, and an air stone can be added to keep algae and other organisms from growing. In hydroponic systems, water purity and PH are important, and many growers use reverse osmosis filters to clean their water. Fertilizers are mixed with water and fed to the plant. About 20% of the water should drain through the medium at each irrigation to avoid salt build up.

In organic systems, PH doesn’t matter, and excessive watering will leach nutrients from your soil, so you want to aim for perfect every time.

Bottom Watering

Bottom watering is a great way to provide perfect hydration for your cannabis seedlings. Water temperature affects the amount of oxygen it can hold, and irrigation water should be kept at 60-70 F (16-21C).

The soil in your pots operates like a set of lungs. When you irrigate fully, stagnant air is pushed out of the soil. As water leaves the soil and moves into the plant fresh air is pulled into the soil. This allows the roots to access plenty of oxygen and benefits microbial growth.

Your plants will need to be in a saucer or tray, and it will take a bit of practice to learn how much water to put in each tray. The volume of water provided should be the amount the soil can absorb in an hour or two.

Pick up each plant every day, and you will become accustomed to the weight of the pots and will know then they are dry enough to water again. If your plant gets droopy, you have waited too long. Plants that share a tray should be of similar size and placed on a flat surface, so they get watered evenly.

Light for seedlings

Cannabis plants love light, and light intensity should be slowly increased during the seedling stage. Lights are usually set for an 18-hour photoperiod and light intensity should max out at about 60% of flowering light levels.

Small plants don’t require lots of real estate.
Two feet of vertical height is plenty of room to install florescent light fixtures and grow your seedlings on wire shelves for a few weeks.
A single 2’x4’x6’ wire shelf can be used to grow 50 or 60 plants for the 2–3-week duration of the seedling stage.

Light fixtures can be attached directly to the underside of each shelf to supply bottom heat to the seedlings on the shelf above. Plants can be grown in nursery flats, and raised closer to the lights when they are small.

Light quality is also important for plant structure. Lights with a blue shifted spectrum promote compact growth. For fluorescent tubes, 4500k spectrum is recommended. Halide lights, or broad-spectrum LEDs work equally well.

Pruning Seedlings

Plants did not evolve in grow rooms and will benefit from being pruned. Some branches are never going to make it to the sweet spot at the top of the canopy. Branches with no future should be removed early to focus your plants energy on the upper colas.

Pruning scissors need to be kept sharp and clean to avoid spreading disease between plants. The best way to sterilize scissors is to mix 15% household bleach with 85% clean water to soak your tools.

Cannabis plants can be trained to grow multiple top flowers. This benefits growers by lowering the final height of the plant and promoting airflow between the colas.

Topping involves removing the growth tip of your plant, resulting in faster development of lower branches.

Topping is an effective training technique but result in a temporary slowing of plant development. Low-stress training (LST) techniques can be efficiently applied to small plants without slowing growth.

Low Stress Training

LST is a great way to shape your plant. Once a seedling has a well-established root system, and 4-6 nodes of growth, low stress training can begin.

Plants are bent over by hand, and a clothespin can be used to clip an upper fan leaf to the pot.
When the top of the plant is at a similar height to lower branches, hormone changes will cause lower shoots to develop more rapidly.
Your plant will quickly recover and turn its leaves up to face the light. This simple step will significantly change the structure of your plant within a few days. Shoots which are not in the best position are pruned so growth is focused on the keepers.
Plants can be bent multiple times using plant ties or training clips to produce many top colas, depending on your needs. You can grow a lot of plants with a few tops each, and flower them when they’re small, or train for more tops and fill your canopy with fewer plants.
If you are growing in a sea of green, you may not want to train at all.

Feeding Seedlings

Plants that are growing in small pots will benefit from a feed or two during the seedling stage.

The best organic fertilizers provide many benefits in addition to nutrients. Amino acids, peptides, and plant growth factors are directly absorbed by plants, saving them the energy of making these compounds.

Living soils will benefit from living fertilizers, so be sure to get a hydrolysate, and not an emulsion. The difference is that hydrolysate is made by fermentation which increases microbial activity. Emulsions are usually heat treated to increase shelf life, killing many of the beneficial beasties that protect our babies.

I like to feed with a balanced 3-1-2 fish hydrolysate during the seedling stage. This is an amazing probiotic. You would probably benefit by drinking some, but you won’t want to once you smell it. The smell of death will quickly dissipate after you feed your plants.

Fertilizer labels are the best source of information for mixing rates. For seedlings, it is usually a good idea to feed at half strength on the first watering after plants are well rooted.

Spraying Plants

Your plants might be precious to you, but for an herbivore they are lunch.

The best practice is to avoid introducing pests to your garden but assume that they will show up at some point. Most sprays that are safe for use in organic growing need to contact the pest to be effective. Spray coverage is easier to achieve with small plants that have been recently pruned.

Spinosad is an organic approved bio insecticide that is effective against many insect pests. This product is made from a soil bacterium that is safe for us but dangerous for bees.
Insecticidal soap sprays will kill most insects on contact. These products are widely available and approved for use in organic agriculture.
Wettable Sulfur is an effective fungicide for use during the veg stage. Sulfur will not stay suspended in water, so you need to shake the sprayer as you are using it.

Sulfur treatments and horticultural oils should never be used together.

Pump sprayers work well for delivery of a fine mist. Plants should not be sprayed under direct light, and good airflow helps plants dry off quickly after spraying.

Pesticide labels contain important information and should be read and followed. Just because something is natural and organic doesn’t mean it’s safe for you. Any excess pesticide should be discarded, and sprayers cleaned after each use.

A strong focus on pest management during the seedling and vegetative stage will reduce pest issues later. I usually spray plants once or twice a week during veg and early flower.

Transplant Timing

You will know when to transplant by observing your plants growth.
Root development is obvious when using root pruning pots, as white roots will be exiting the pot everywhere.
Basic plant structure should be established, with 4-6 tops at similar height ideal for most growing systems.

Plants are not fond of being moved between different environments. If you are moving plants to a different location, it is best to let them acclimate to new conditions for a day or two before transplant.

For outdoor growers, transplant timing can sometimes be dictated by mother nature. If clones are planted outdoors too early, they may start to flower prematurely and ruin your crop. A great way to keep your plants happy if transplant gets delayed is to pot them up into a larger pot for a couple of weeks.

Grow lights do not contain much UV, and seedlings that have been growing under lights should be hardened off before being planted in direct sunshine. Plants can be placed in a mostly shady area for a day or two or covered with a crop cover to allow them to acclimate to outdoor conditions.

Transplant to Veg

Taking care in how you transplant will help to limit shock. Plants should be allowed to dry out a bit, then top watered a day or so before transplant. When the soil is damp on top and dry on the bottom, the root ball will slide easily out of its pot.

It is best to transplant your seedlings into soil they are familiar with. Plants that are going into outdoor beds will benefit from a bit of potting soil around the root ball at transplant. Roots will quickly establish in this familiar media before expanding into the beds.

When your seedling has been transplanted, the new soil level should just cover the surface of the root ball. Water in your new plant generously to make sure there are no air pockets between the root ball and the new soil.

Once your transplant has been properly set, there should be plenty of water available in the soil to sustain the plant for at least a few days. It is best to delay the first watering to allow the soil to dry as much as possible, without the plant getting droopy, to encourage root expansion.

Your plants will be so happy in their new home! It is normal for a plant to focus on root development following transplant, and you may not see much growth for a few days. Once the roots have grown into the new soil, your plant will reward you with explosive growth.

You have one opportunity to get the seedling stage right. Cannabis plants are resilient and can recover from a stressful start, but the best crops maintain growth momentum from germination to harvest.

Amazing Weed Starts with a Vigorous Seedling