2 Week Old Seedling (Problems, Fixes, Tips)

Cannabis is very resilient, but 2-week-old seedlings are very vulnerable to a whole host of things going wrong, which is why growers should be on their toes during this crucial stage.

In this article, I’ll explain what a healthy 2-week-old seedling should look like, what the ideal environment for a seedling is, and also go over some common problems (and solutions) that growers face during this delicate phase.

What should a healthy 2-week-old seedling look like?

Healthy 2-week-old seedlings should have upright stems, be displaying 2-3 sets of ridged ‘true’ leafs, and be roughly 2-3 inches tall (depending on the strain and growing conditions) Your seedling’s leaves should be a vibrant green color with no yellowing, brown spots, or drooping.

The Ideal environment for a 2-week-old seedling

Before we start looking at individual problems, let’s take a look at the ideal growing conditions for cannabis seedlings at the 2-week stage.

If your seedling’s environment is significant;y different to this, you may be able to diagnose the issue yourself.

Pot size

If you’re growing a photoperiod strain, it’s better to grow in a small plastic cup before translating to a larger container (3-gallon, 5-gallon, 6 gallons, etc) By growing your seedling in a smaller container first, you are reducing the risk of overwatering and root rot, as larger volumes of soil will hold moisture for longer. Smaller pots also encourage lots of healthy root growth.

If you are growing an Autoflower, then it’s better to plant your germinated seedling directly into its final container. Autos don’t deal with stress very well, and transplanting them can cause issues with flowering that can lead to seriously reduced yields.

Humidity

The ideal humidity for a 2-week-old seedling is 65% to 85%, which reduces to 45-65% after week 3. A higher humidity helps your seedling establish strong roots by absorbing moisture through the leaves. Purchasing a simple Hygrometer like this will help you keep track of your grow room humidity. If your grow room humidity is below 65%, you will need to purchase a humidifier, and your humidity is above 85%, you will need to purchase a dehumidifier.

Temperature

seedlings like warm and humid conditions. The ideal temperature at soil level should be 72-82°F/22-28°C. Again, a simple Hygrometer should be placed at the soil level to make sure that you are keeping within this range. If your temperature is outwith these ranges, you will need to adjust your grow light height and ventilation. I live in a very cold environment, so I actually have to run a heater in my grow room in winter to maintain these temperatures.

Lighting Distance

The distance that you should keep your lights from your seedling depends on the type of light that your using and its power output. If you are using an LED grow light, then the manufacturer should provide the recommended distance. For most lights (including MH/HPS) this will be somewhere between 24-36 inches above the canopy. If your grow light is too close to your seedlings, they will start to burn, but if they are too far away, they will start to stretch.

Lighting schedule

I find seedlings do best with a lighting schedule that mimics natural outdoor conditions. I like to use a schedule of 18 hours with the lights on and 6 hours with the lights off. However, it’s important to remember that when your lights go off at night, your grow room temperature will drop, so if you live in a cold climate, make sure that your grow room temperature doesn’t drop below 15°C. If it does, buy a portable heater to keep the temperature up, or consider running your grow light 24/7.

Air circulation

Proper air circulation in your seedling’s grow environment is vital. 2-week old seedlings should have a fan blowing a light breeze over them to help strengthen their stem. The seedlings should be gently rustling and no more. Too much wind will damage your seedlings. This is a process called “hardening off” and will make your seedlings more resistant by encouraging their roots to span out and have a stronger foundation. This process is especially important if you plan on growing your plants outside.

Problems With 2 Week Old Seedlings

Let’s take a look at some of the most common problems faced by growers at the seedling stage, how you can fix them, and how you can stop them from happening in the future.

1. 2-week-old Seedling is Yellowing

Yellowing leaves on a 2-week-old seedling could be due to a number of reasons.

Overwatering & underwatering

The most common cause of yellowing seedlings is overwatering. When you overwater your seedlings, you are preventing their roots from getting to the oxygen they need to grow. You are literally drowning them.

Overwatering is very common and even experienced growers (myself included) overwater plants from time to time.

Common symptoms of an overwatered seedling are:

  • Drooping leaves
  • Soil not drying out after 3 days
  • Algae growing on top of soil
  • Yellowing leaves
  • Slow growth
  • Firm leaves

Underwatering is less common but causes the same reaction (drooping and yellowing leaves) as overwater, so be careful not to confuse the two. An underwatered seedling will be in bone-dry soil and is usually caused by the grower not accounting for the seedling requiring more water as its roots start to span out.

How to fix overwatered seedlings

if you think that you have overwatered your seedlings, here is what I recommend that you do, step by step.

1. Stop watering so often (duh)

insert pic of solution

The first and most important thing step is to adjust your watering schedule. When it comes to watering 2-week-old seedlings, less is definitely more. Stop watering your seedling until the soil has completely dried out. I can’t stress this enough, the soil must have completely dried out before you water your seedling. The time it takes for your soil to dry will be different depending on your environment, but in general, most soil should dry out after 2-3 days. To make absolutely sure that your soil has dried out before you next water it, stick your finger a half inch into the soil. If the soil is dry then it’s OK to water again.

2. Go easy on the water

2-week old cannabis seedlings actually require very little water. They have tiny root systems which simply can’t absorb large quantities of water. I use a spray bottle to wet the surface of the soil until the second node appears. I’ll check the seedlings regularly and if the soil has dried out then I’ll give them another quick spray. Once the second node appears, I switch to soaking the cup completely by pouring water evenly around the cup until water starts coming out of the holes in the bottom (called runoff) This is how I’ll water the plant for the rest of its life. If your seedling is planted in a larger container already, then make sure that you are only watering in a small circle around the seedling and not watering the entire container.

3. Check your drainage

If your seedling is in a small plastic party cup (or similar) make sure that you have some holes poked in the bottom or sides. This stops water from pooling at the bottom of the container and reduces the available oxygen for the roots of your seedlings. If you already have some holes in your container, make sure that they are not clogged.

Heat Stress

Another cause of cannabis leaves turning yellow is heat stress. When the temperature of your lights is too much, your plants become stressed and start to turn upwards. The leaves will usually have yellow and brown spots in the areas that are most affected, and might even start to appear bleached.

How to fix:

1. Move your grow light

The temperature at soil level should be 72-82°F/22-28°C. If you don’t already have one, place a simple hygrometer at soil level and ensure that the temperature does not go above 82°F/28°C. If the temperature is too hot, move your light up until it’s within range.

2. Improve your air circulation

Point an oscillating fan at your seedlings so that they are gently rusting in a breeze. This will strengthen their roots and also help decrease the temperature and protect them from grow light ‘hot spots’. Just be careful not be too strong with the fan, as too strong a breeze will damage your seedlings.

2 Week Old Seedling Stunted Growth

If your 2 week old seedling is less than 2 inches tall, then it’s growth is not where it should be. Here are the main reasons why this happens

Environmental Stress – if your seeds are too hot, too cold, too dry, or too wet, they are going to grow slowly due to the stress that they are under. Make sure that your temperatures (72-82°F/22-28°C) and humidity(65% to 85%) are in the ideal ranges, and make sure that your grow light is not too close.

Overwatering & underwatering – an overwatered seedling won’t grow quickly because it cannot access the oxygen it needs from the wet soil. An underwatered seedlings root system will dry up and not be able to absorb the nutiorents required to grow big.

Strain type – some strains simply grow at a slower rate than others. I’ve grown the same strains under the same conditions and had them grow at different rates. This can be caused by anything from tiny genetic differences to how the seeds were stored.

2 Week Old Seedling Looks Strecthed

If your two-week-old seedling looks stretched or ‘leggy’ (like the picture above) then your grow light is too far away from your seedling. Your seedling is trying to find more light (food) and is stretching toward to the light to try and find some

How to fix

Move your light closer to your seedlings. Your grow light should be roughly 24-36 inches above your seedlings. Most grow light manufacturers provide an optimal height for seedlings based on the wattage of the light, so always default to that.

2-week-old seedling FAQ

Here are a couple of answers to some common beginner questions about 2 week old seedlings.

How big should a 2-week-old seedling be?

Depending on the strain, a 2-week-old seedling should be around 2-3 inches and be displaying 2-3 sets of ridged ‘true’ leaves.

How far should a 2-week-old seedling be from a LED grow light?

It depends on your grow light. Most grow lights come with a recommended distance. However, in general, an LED grow light should be 24-36 inches above your seedlings.

Can you tell the sex of a 2-week-old seedling?

2-week old seedlings will not show sexual maturity. Many growers mistake stipules and new leaf growth for male pre-flowers. Your plant will start showing sexual maturity between weeks 4 and 6.

How many hours of light does a seedling need?

For optimal results, seedlings require 18 hours of light and 6 hours of darkness each day. The 6 hours of darkness give your seedlings a small rest period.

When should your transplant a 2-week-old seedling into a larger pot?

You should wait until your seedling has at least 4 sets of true leaves. By this time, your plant should have a fairly well-established root structure.

James Alexander James Alexander
Hey, I'm James! The founder and head writer here at GreenBudGuru.com. I started this site to share my passion and knowledge of all things cannabis. I used to work as a budtender in central Amsterdam, and have over 7 years of growing experience.

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