How to Care for Seedlings

By: Soft Secrets, December 12, 2012

Growing from seed is great: there are a vast range of seed banks to buy from and, unlike growing from clones, you get to choose the exact variety you want to grow – rather than relying upon whatever cuttings are going around at the time. Learning about germination over the winter will help to prepare you for springtime sowing.

Growing from seed is great: there are a vast range of seed banks to buy from and, unlike growing from clones, you get to choose the exact variety you want to grow – rather than relying upon whatever cuttings are going around at the time. Learning about germination over the winter will help to prepare you for springtime sowing.

The first ten days after germination can be the most crucial of your plant’s life. Just like a newborn baby, your girls are vulnerable to the elements and are totally dependent on you to give them the best start. Lots of growers (both new and experienced) lose plants at this stage, get disheartened and move away from using seeds altogether. However, taking care of seedlings does not have to be difficult. Just follow a few simple rules and you will raise healthy seedlings, time after time.

Two freshly ‘popped; beans, germinated using the paper tissue method

Pre-Germination Tips

Some of the problems associated with bringing up seedlings can stem from the fact that not all of your seeds will germinate at the same time. For example, keeping the vents on a propagator closed while you wait for all your seeds to show can lead to the germinated seedlings rotting or ‘damping off’.

To avoid these problems, you may choose to germinate or ‘pop’ your seeds before you plant them in their growing medium. This way you can be sure that you have selected the healthiest seeds, and will not be waiting around for the weaker ones to germinate.

There are a couple of tried and tested pre-germination methods:

  1. Cup of Water: Take a cup of mineral water and leave it for a few hours to bring it up to room temperature. Put your seeds into the water and break the surface tension with a (clean) finger so that the seeds sink. Place the cup in a dark place that stays at a constant temperature, preferably between 66° to 75° F.  Within 24 to 48 hours the seeds will have cracked and the tap roots will show. The seeds can be left in the water until the tap root protrudes a few millimeters, and can then be planted out.
  2. Paper Tissue Method: Sandwich the seeds between pieces of damp tissue or paper towels and place them in an airtight container, zip-close bag or between two dinner plates, the top, upturned plate acting as a lid. Place in a warm, dark environment – an airing cupboard or on top of a fridge or DVD player – where warm air is constantly vented out. The seeds should germinate within 48 hours and can then be planted.

Ensure that you plant the seeds a few millimeters under the surface of your chosen growing medium with the tap root pointing down. Within a couple of days the seedlings will break through and you won’t be left waiting around for any runts.

Choose the Correct Environment

The first set of ‘true’ leaves beginning to show

Without a doubt, the absolute best environment for a young seedling is a propagator. Seedlings need consistency in order to grow healthily; that means consistent temperature, humidity and air flow. A propagator provides this consistent environment. Any changes to these environmental factors need to be done as gradually as possible, to prevent shock, and it is easy to do this with a propagator.

In its simplest form, a propagator can be made from any material that allows light to reach the seedling and maintains a constant environment by trapping heat and humidity inside it. A clear plastic bag, set over the top of a pot and attached with an elastic band, forms a cheap-yet-effective propagator!

Your local hydro shop will stock inexpensive plastic propagators that comprise of a seed tray and a clear plastic lid or humidity dome. The lids often have adjustable vents that allow you to control the airflow and humidity levels inside the propagator. When seeds first germinate, you need to maintain humidity of around eighty percent – this is done by keeping the humidity vents closed, which stops airflow and prevents moisture from escaping.

Once all seedlings are showing, gradually open the vents a little each day. This will increase the airflow and decrease the humidity (a process known as ‘hardening off’), and gets the seedlings ready to be moved into the main room. It also prevents damping off. After ten days, the lid should be fully removed and your seedlings will be ready for transplanting.

The ideal root zone temperature for seedlings to develop is between 66° and 72° F. Keeping temperatures uniform across all seedlings will ensure that they develop at the same rate and are ready to transplant at the same time. This can be achieved by placing your propagator onto a heat mat or, if you are germinating lots of seedlings, investing in a heated propagator.

Use the Correct Light

A healthy little sprout in the dirt

Once your seeds have germinated and have broken through the surface of the growing medium, they will begin to photosynthesize and must have light for a minimum of eighteen hours per day.

Although it is certainly possible to start Cannabis plants on the windowsill using natural sunlight, this method has its problems – the main one being that the sun is not as consistent as a grow lamp. A hot, sunny day is difficult to plan for and you could return home to a windowsill full of wilted plants. Seedlings are vulnerable and can wilt within hours if the conditions are wrong. Direct sunlight can fry them!

If natural light levels are poor, the seedlings will stretch for light, leaving you with long, spindly plants that only develop small yields. Remember, if you are growing indoors, you need to maximize the available headroom under your lights. You need to keep plants short and squat until they are ready for flowering; otherwise, you are wasting space on long stems, rather than long buds! Why spend good money on seeds and then risk losing all of your plants on the windowsill? It makes sense to invest in some indoor lighting.

When plants are very small, excessive heat and light can stunt their growth or even kill them. For this reason it is not practical to start them under an HID lamp; you will certainly be wasting money if you do, as you will need to place the lamp a good distance away from the seedlings (so heat and light are not used efficiently and are, therefore, squandered).

Fluorescent lighting is less intense and gives off less heat, so is much more suitable for very young plants. The propagation lighting available from your local grow shop, such as T5 propagation strips or CFL ‘eco-lights’, will have an output in the blue-white spectrum; this encourages plants to develop roots and grow outwards rather than upwards, and will see your plants through the propagation phase and into the early vegetation stage of growth.

These fluorescent lamps are cheaper to purchase and operate than HID lighting and, because they give off much less heat, they can be placed closer to your seedlings – so you waste very little light. A single, 24-watt T5 strip light will not cost very much from your local grow shop. This would cover ten to fifteen seedlings in a small propagator. Bargain!

Feed at the Right Times

Before planting your seed, your growing medium should already be moist, but not completely saturated. Peat or cocos plugs should be soaked in water until they are fully expanded and then allowed to drain overnight. If you are using rockwool cubes to propagate, soak them in a solution of quarter-strength nutrient that has had its pH adjusted to 5.5, and allow them to drain overnight before using. As discussed, the main objective when propagating your seedlings is to quickly establish a healthy root zone. To do this, it is good to understand the effects of watering the root zone.

Invest in a propagator. Your girls will love you for it!

Roots grow in response to depletion zones (i.e., outward to search for water and food). When a root has absorbed all of the available water and minerals in one area of growing medium, it grows outward to find more. This is how the plant fills the growing medium with roots. Therefore, it is essential to allow the growing medium to dry out before re-watering. This allows the roots to use up the majority of the food and water present.

When water and food is always available, the roots do not need to search out for them and the root zone will be underdeveloped. Obviously, it is very important not to over-water seedlings; however it is a balancing act, as under-watering will cause the roots to die back – this also limits development.

It is worth remembering that seedlings are tiny, and are unlikely to need any additional food or water for the first three to five days after germination. If in doubt, you can purchase a soil moisture meter to double check.

The first feed can be given to your seedlings once the first real or ‘true’ leaves appear: these are the second set that develops after germination. Do not feed stronger than an EC level of 1.2, including background EC. Always stay on the cautious side with your feed, as it is easy to give additional food if your plants need it, but very difficult to correct over-feeding with very young plants.

Learn to read your plants. As a general rule, if the lower leaves start to yellow, they are hungry. If the edges of the leaves are brown or curling, they are over-fed.

Transplant with Care

If you have started your seeds in a propagation medium such as rockwool cubes, peat or cocos pellets, then within ten days of germination they should be ready to transplant on towards the next stage. Even seeds started in a small three-inch pot of soil or cocos will probably be ready to move up a pot size within two weeks of germination. The seedlings will still be vulnerable at this stage, so the main goal is to minimize transplant shock.

As leaf sets develop, the plant exits the germination phase (© Shutterstock)

For best results – and to minimize shock – transplant into the same growing medium that you started in: for example, seeds germinated in soil should be transplanted to a soil pot, cocos to a cocos pot. This will speed up the time the seedling takes to root after transplanting.

The exception to this rule is rockwool, which provides an inert, sterile starting block that can be transplanted to any medium. Each block is completely uniform to the next, so each seedling will grow consistently and will be ready to transplant at the same time.

Contrary to popular belief, when transplanting into a new medium, it is a good idea to not water on the day of transplanting. It is likely that the seedlings will have suffered some root damage when they were transplanted; watering immediately can introduce pathogens into the damaged roots. It is best to wait until the next day and then water with a dose of plant stress reliever, such as SuperThrive. This will also help to prevent damping off.

It is also worth mentioning that you can bury a plant up to the first node (or branch) when transplanting. This allows you to shorten the height of individual plants and ensures an even canopy. This technique can be done at every stage of potting-up.

Timing is key for successful transplanting – you want the roots of the seedling to have appeared on the outside of the propagation medium. Transplant too early and you can stunt top growth as you wait for the roots to fill out the medium. Transplant too late and the seedling may become root-bound in its cube, become dehydrated or begin to develop deficiencies. If your seedlings begin to yellow then they are in need of food, and need to be transplanted up and given additional nutrients.

Once seedlings have been transplanted into their new pots or cubes, they can be put back into the propagator for a couple of days before hardening off and going into the main grow room.

Label Up!

Labeling your seeds when you sow them is really a must. When growing more than one strain at a time, one thing that catches out even the most experienced of growers is forgetting which plant is which! No matter how good your memory is, after a couple of joints, that stoned visit to your grow room will inevitably lead to the seedlings getting mixed up.

Different strains may need different levels of feed, so it is well-worth remembering which is which.  Use plastic stake labels rather than wooden ones, as they are easy to clean and reusable. In some instances, damp wood can harbor the larvae of certain grow room pests.

Now, get to germinating!

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