How To Take Care Of Seedlings


Growing from seed is great; there is a vast range of seed banks to buy from and – unlike growing from clones- you get to pick whatever variety you want to grow rather than relying on whatever cuttings are going around at the time.

The first 10 days after germination can be the most crucial of your plants life. Just like a new born 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. But taking care of seedlings doesn’t have to be difficult. Just follow a few simple rules and you’ll raise healthy seedlings, time after time. 

Pre-Germination Tips 

Two freshly ‘popped’ beans. Germinated using the tissue paper method

Some of the problems associated with bringing on 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 into their growing medium. This way you can be sure that you have selected the healthiest seeds and won’t 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 in 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 19-24°C.  Within 24-48 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 millimetres 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, ziplock bag or between two upturned dinner plates. 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 millimetres 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 

First set of true leaves beginning to show

Without 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’s 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 sat over the top of a pot and attached with an elastic band, forms a cheap but effect 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 80%, this is done by keeping the humidity vents closed, which stops airflow and prevents moisture from escaping. 

A healthy little sprout in the dirt

Once all seedlings are showing, gradually open the vents a little each day, this will increase the airflow and decrease the humidity, this process is called hardening off and gets the seedlings ready to be moved into the main room. It also prevents ‘damping off’. After 10 days the lid should be fully removed and your seedlings will be ready for transplanting up. 

The ideal root zone temperature for seedlings to develop is between 19 - 22°C. 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’re bringing on lots of seedlings, invest in a heated propagator. 

Use The Correct Light 

Once your seeds have germinated and have broken through the surface of the growing medium, they will begin to photosynthesise and must have light for a minimum of 18 hours per day. 

Although it is certainly possible to start Cannabis plants on the windowsill using natural sunlight, this method carries 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 window sill 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’re growing indoors, you need to maximise 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 a HID lamp, you’ll certainly be wasting money if you do as you’ll need to place the lamp a good distance away from the seedlings (so you’ll be wasting heat and light). 

Fluorescent lighting is less intense and gives off less heat, so is much more suitable. 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, 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. 

In the UK a single 24 watt T5 strip light will cost as little as £20 from your local hydro shop. This would cover 10-15 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 coco plugs should be soaked in water until they are fully expanded and then allowed to drain overnight. If you are using rock wool cubes to propagate, soak them in a solution of quarter strength nutrient solution that has been pH’d 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. 

Roots grow in response to depletion zones, i.e. outwards 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 outwards 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 don’t 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 and this too limits development. 

It’s worth remembering that seedlings are tiny and are unlikely to need any additional food or water for the first 3 to 5 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 leaves appear; these are the second set that develops after germination. Don’t feed stronger than an EC level of 1.2, including background EC. Always stay on the cautious side with your feed, it’s easy to give additional food if your plants need it, but it’s 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 overfed. 

Transplant With Care 

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

If you’ve started your seeds in a propagation medium like rock wool cubes, peat or coco pellets then within 10 days of germination they should be ready to transplant onto the next stage. Even seeds started in a small 3 inch pot of soil of coco will probably be ready to move up a pot within two weeks of germination. The seedlings will still be vulnerable at this stage, so the main goal is to minimise transplant shock.  

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

The exception to this rule is rock wool, which provides an inert, sterile starting block which 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’s a good idea not to water on the day of transplanting. It’s 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 water in with a dose of plant stress reliever, like SuperThrive. 

This will also help to prevent root rot or ‘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 feed. 

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! 

Labelling 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’s well worth remembering which is which.  Use plastic stake labels rather than wooden ones, they are easy to wipe and, in some instances, damp wood can harbour the larvae of certain grow room pests. 

Now get germinating!!

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