Amsterdam Seed Center

Grow info

In this article we'll try to provide you with the basic info to produce the most successful harvest from your precious cannabis plants.

Germination of your cannabis seeds:


Germination of cannabis seeds in a glass of water

You can germinate your seeds directly in soil. Place your seed at a depth of 5mm to 1cm in specialist seed/seedling soil that is moist (but not soaking wet). It needs to be a balanced soil, with a pH of around 6 and without high levels of nutrients. You can buy this specialist soil at any regular garden center as the same soil is used for growing all varieties of seeds. It’s a good idea to create your own micro-climate with a plastic covering (see below). This can be removed after the seeds begin to shoot and appear above the soil after approximately 3 to 7 days.

If you're growing with a hydroponic system you can also put the seeds directly in soaked rockwool cubes or mapito. Use water with a pH level of 5.5 to soak them, arriving at a pH of around 6 in the block. At this point, the seedlings are able to transport all nutrients that are required for them to grow. Be very careful at this stage as the plants can easily burn and dry out. That’s why you should keep the baby plants moist and not give them too much fertilizer.

You can also germinate cannabis seeds in between wet tissue or cotton wool, which you keep moist and in the dark, at room temperature. After a couple of days they will have sprouted and will be ready to be transplanted into little pots with soil, preferably special soil for seeds/seedlings.

However the best way to germinate your cannabis seeds, in the opinion of Amsterdam Seed Center, is to germinate them in a glass of water. You can use tap water, but if your water is particularly chlorinated, then reach for the Evian! Definitely don’t use warm water and make sure it’s not too cold either. After about 24 hours the seeds will sink to the bottom - as they take up some water - and the next day the first signs of germination should appear. Once your seed has a root ‘tail’ of about 1.125cm or ½ inch, the germinated seeds are ready to pot. As with the technique for directly potting without pre-germination, place your cannabis seeds in moist yet airy soil at a depth of 5mm to 1cm.

Seedlinq under cokebottle as propagator

A neat trick to create a mini propagator (mini glasshouse) is to cut a plastic Coke bottle in half and place it over the seedling. When the little plant has become too big to fit the bottle it's ready to grow on its own and, if desired, can be transplanted to a bigger pot. The temperature should be around 20 to 24 degrees Celsius (70 F).

For even more info about germinating cannabis seeds CLICK HERE and have a look at our "Popping beans" article.


Cultivation of cannabis outdoors

Once the cannabis plants are big enough, 15-20 cm (6-8 inches), they can be planted outdoors in rich soil, either in the ground or in large pots. In the south of Europe, or other warm and sunny regions, this can be as early as March (or September in southern latitudes), while in colder countries like Holland one should wait until the beginning of May. Outdoors, the development of your marijuana plants is determined by the amount of sunshine, rain and wind they are exposed to. It’s your task to help nature by providing sufficient water and nutrients and if possible to protect them from heavy showers, especially towards the end of flowering. Outdoors, some cannabis plants can grow over 3 meters tall! When the hours of light per day drop under 15 hours, the cannabis plants will start to bloom. The plant and yield can become very impressive with some luck and favorable weather during the last couple of months. If conditions are right, they will produce a lot of buds - anything up to a kilo per cannabis plant.

Cannabis cultivation in green houses and polytunnels

The quality of cannabis plants grown in greenhouses will be better than cannabis plants grown outside. They can grow like indoor cannabis plants, having the big advantage of sunlight - nothing is stronger than sunlight - yet being protected from rain and cold. Here, the marijuana plants can be well controlled and if you artificially shorten the light cycle to 12 hours, by covering the plants or the whole greenhouse, you can even harvest in the middle of summer.  With some good organization in the greenhouse, it is even possible to fit in two harvests in a year.

Cannabis indoor growing

Indoor grow at Amsterdam Seed Center

Home growing has become very popular, which is not surprising when you consider you can supply yourself with top quality product that is also economical. One of the problems with buying cannabis from different sources is you have no idea where it has come from and who has grown it. The bud you smoke may be contaminated with high levels of pesticides, left-over nutrients due to insufficient flushing, or fungi like bud-rot / mold or mildew. By growing your own cannabis and being in control of your crop, you know where your plants have come from and, if you treat them right and give them what they need, the rewards are huge! 

The quality of indoor cannabis plants is often very high. Under high pressure sodium (HPS) lamps, or using LED lights, it is possible for almost everyone who has a little space available to grow their own. Indoor growing is a little more complicated because you have to control the whole environment, but your effort will be rewarded once you have the conditions right. Then it is as easy as anything, and you can repeat the winning formula time after time! Make sure the temperature does not exceed 30 °C (86 °F) or get cooler than 18°C (68 F). In perfect conditions the difference in temperature between lights on and off should be no more than 10 degrees C. The room should be well ventilated and constantly refreshed with air. To create this refreshing of the air you need an extractor fan and the air should be extracted through a carbon filter to keep that fantastic fragrance of cannabis inside your grow room and not shared with your neighbors. Enclosed humidity should be around 80% during the growing period, but needs to be lower than 50% at the end of the flowering period to prevent mold.

Before you start, we advise you to read a book on growing, check out articles on the internet (many of the seed companies we stock have excellent on-line guides to help answer your questions) or get yourself informed by other growers who have someexperience. Although growing indoors isn’t difficult, having some knowledge of the basic techniques is definitely a big advantage.


Marijuana plants can best absorb all necessary nutrients at a pH value of 5.5 - 6, making sure all nutrients are transported within the plant. This way the whole of the cannabis plant thrives, which results in maximum growth and leads to more quantity of top-quality weed. During different stages of their life, cannabis plants require different types of nutrients, as well as different levels to achieve an optimum yield . Many nutrient companies have a schedule for the optimum dosages to use with their products. You can also use biological stimulators, such as rooting and flowering stimulators, that activate the organic bacterial life (or micro-organisms), and therefore make the plant stronger and healthier. Some of these stimulators can make quite a difference.

Regular seeds (non-feminised)                                                                             

To have flowers (buds) you'll need to grow female plants. Male plants will only develop pollen in order to pollinate the female flowers and produce seeds in order to 'survive'. When the female plants are not being harvested - like in wild nature - they die and the seeds they've produced drop to the ground where they hibernate until next spring, when they will grow into a  new plant. This process is part of nature’s life cycle. Therefore, when growing plants to consume the flowers, you don’t want seeds in your buds. Apart from making the plants less potent, smoking or vaporizing seeds is no good for you and may very well even give you a nasty headache! To prevent the plants making seeds, you have to remove the male plants by “sexing’’ them. The males are of no use other than to reproduce or breed with.

The female plants are the ones to keep, as they produce the wonderful tasting and highly appreciated effects on the body and mind with their beautiful flowers, or BUDS to use their more common name! Cannabis male and female plants are alike at the vegetative stage and sex shows only when the flowers start to appear. From that moment on, cannabis plants become distinguishable and the male and female look quite different. In the pre-flowering stage, one can sex the plants by looking for the males to throw away. You should look at the main stem, at every internode, to find the flowers. Most likely you will find them in the upper part of the plant. Another good tip is to check the internodes for the development of tiny ‘balls’ (yes really!) as this is the easiest way of identifying male plants.

Feminized seeds are harvested from female plants that were pollinated by 'reversed' female plants. These plants are genetically modified to produce female seeds and female seeds only.

Last but not least, AutoFlowering cannabis plants. Sometime in the 1940s, the so called Ruderalis plant was discovered in the south of Siberia. It's a hardier variety that grows naturally in the northern Himalayas and parts of Russia, characterized by a more sparse, "weedy" growth. Since the 1990s various breeders have been crossing the Ruderalis with strong cannabis varieties, to create an automatically flowering cannabis plant that produces great weed in a relatively short period. Fast froward to 2016  and the now named Auto Flowering variety is especially popular amongst outdoor growers in colder climates like The Netherlands, Germany, Belgium, North parts of France, United Kingdom, etc. As well as in colder climates, autoflower plants are also very convenient for growers living close to the equator, where plants tend to flower almost straight from seed due to the short days in this part of the world.

The Harvest

Manicuring your cannacrops...

You should only harvest when the flowers are ripe – not before, but also not long after they are ready! Yes, it is something of a balancing act and you will need patience and vigilance… and a magnifying glass is very useful too! It is time to harvest when the resin glands are swollen to their maximum size, which you can best see with your magnifying glass. The trichomes, or crystals, should be a 50/50 mix of milky/cloudy and amber. Another, although less accurate, way is to watch if the buds are still getting fatter with new growth. When this process of daily production has stopped and most of the little stigmas (hairs) on the flowers have turned from white to brown-orange, it is time to harvest the plants. First take off the big fan leaves, then hang the marijuana plants upside down in a cool, dry and dark place to dry out. About 14 days later, you can trim off the last few leaves so that only the buds remain. Now you are ready to experience your own home grown, quality super buds! There are in fact two ways to harvest your precious weed. Dry trim or wet trim. Have a look at the differences in our article "The harvest and beyond".

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