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breeding pollination remove powdery mildew on cannabis seeds


In honour of April 20, the International Cannabis Holiday here’s your guide to growing Cannabis plants for your own use this summer.

Ontario law allows each residence to grow up to four cannabis plants without a special license. If you’d like to grow more–and stay on the right side of the law–you’ll need a prescription from your doctor, and a grow license from Health Canada.

Modern cannabis is a hybrid of indica, sativa and ruderalis species. Some strains are high in THC, which has higher psychoactive elements, some in CBD—medicinal, used to counteract pain. Expert breeders have been crossing and back-crossing to improve plants’ genetics: their potency, flavour, aroma, height, vigour, yield, and resistance to disease. It’s fair to say that cannabis is stronger now than it was in the 60’s and 70’s—thanks to crosses and superior cultivation. Average THC in cannabis was 1% in the 70’s; grew to 8.5% in 2008 and it’s likely even higher today.

Cannabis is tough, tolerant and easy to grow–the nickname weed might give you a hint in that regard–and you can grow it outside during the summer, or under lights indoors. If you can successfully grow tomatoes or peppers in your vegetable garden, you can grow cannabis. The plants are tolerant of most situations, but they demand full sun–as much as you can provide. Ideally your garden will also be sheltered from the wind since cannabis branches tend to be brittle and they can snap. The plants will get very large and will absolutely require staking and support, since the branches get very heavy when they are in bud.


Cannabis grows easily from seed and thousands of strains are available for purchase online, with differing quantities of THC or CBD, depending on your preference. The average price is around $10-$20 per seed. Sowing cannabis is straightforward: simply press them into damp seed mix, cover lightly and keep the mix moist. Most seeds germinate in 2-5 days and once the seedlings have at least one pair of true leaves they can be potted on individually.

Cannabis is a dioecious annual plant–which means both male and female plants are required for pollination. It is important to buy only feminized seed.The highest concentration of cannabinoids is found in the female flowers. Most seed retailers only sell female seeds, but there is still always a small chance of a male plant germinating. If a male plant is found, the plant must be culled to prevent pollination. Some are hermaphrodites and will display intersex traits; they should also be removed. There are several reasons for this: 1)if a female plant is pollinated, energy goes into seed production, not cannabinoids, which lowers THC/CBD; 2) male plants won’t produce the large resin-filled flowers growers value; 3) if a male plant is allowed to pollinate the females, the resulting flower buds will be full of seeds and of poor quality.

There are two basic stages to your cannabis plant’s life:

  • Vegetative Stage
  • Flowering Stage.

Vegetative Stage

This stage is between two to eight weeks depending on cultivar, and your goal is to get the plant as large as possible before it flowers in order to increase the yield. During this stage, the plant is fed and watered and each plant has its branches heavily staked, to prevent the weight of the buds snapping off the branches. The lower and inner leaves are trimmed to allow air circulation, and the plant is pruned into open shape to let the sun into interior.

Cannabis loves heat and needs FULL sun. That means 6 to 8 hours direct sunlight through the middle of the day!)

It’s best grown in rich, organic soil, so it’ll be perfectly happy growing in your vegetable garden, if you have the space. Cannabis plants are vigorous growers and respond well to sunlight and nutrients; some plants can get up to 10’ tall and wide—depending on the hybrid.

A general all-purpose fertilizer like seaweed, is ideal to use, but many growers don’t bother to fertilize at all if the plant is growing in good organic soil. As the plants grow, monitor them for pests and disease–though there are very few that will attack cannabis plants grown outdoors. You will need to watch in case your plants turn out to be males or hermaphrodites; you won’t know until they begin to flower, but you must destroy them or you’ll ruin the rest of your crop.

One serious concern is to monitor for mould and powdery mildew, especially if there is a lot of precipitation late in the growing season when your plants are in flower. It’s a good idea to tent the plants with clear plastic to prevent moisture from getting to the flowers. Also, be sure to water only from the bottom to keep foliage dry.

Flowering Stage

Cannabis grown outside will go into flower when the hours of daylight and darkness are even. Getting to bloom stage is completely dependent on the strain of cannabis that you chose to grow. When the light levels are optimal, the plant will switch over from growth of leaves, to flower production, and the length of time the flowers take to mature varies, depending on the plant’s genetics. For example: auto-flowering strains will begin to bloom at 30 days, and sativas flower in 10 -14 weeks. Feed and water your plant while it’s in flower, and remove the larger lowest leaves to direct more nutrients to bud formation.

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Each flower is covered with translucent resin glands, concentrated on the buds. The goal of the grower is grow the largest colas or flower buds–not much different from growing the largest tomato. As cannabis buds develop, they become sticky with resin, which contains the trichomes that hold the medicinal elements. You should look closely at the flower buds daily–a small magnifying glass will help. You will know the flower is ready by visual clues: size, smell, trichomes, density of bud—and especially colour. The resin coating the pistils will become milky or amber in colour, rather than clear. When the resin is amber, the bud is mature and all the trichomes, flavonoids and cannabinoids are at maximum development. If harvest is delayed they will begin to lose quality, so don’t wait too long.


When your buds are mature, cut the branches and remove the large fan leaves then hang the branches upside down to dry. You can leave the smallest trichome leaves around the flowers and trim them off once the buds are dry.

Hang them for 1 -2 weeks, out of light and make sure there is enough air movement in your drying room. When the branches snap and break instead of bending, trim off the buds and cure them.


Curing is not critical but doing it improves the storage time of your cannabis, as well as its quality and potency. Place the trimmed buds into sealed glass jars kept in a cool dark place. Heat and light will quickly degrade the essential oils containing the precious terpenes, cannabinoids and flavonoids. For 2 weeks, open the jars daily to “burp them” releasing the moist air and replacing it with fresh air. Then you can store the buds indefinitely in the jars, in a cool dark place.

Indoor Grow

If you prefer to grow indoors, you will need to give your plants as much artificial light as possible. Cannabis will not grow as a houseplant, or on a sunny windowsill. You will need to provide artificial light–either from LEDs or a HID (High Intensity Discharge), like High Pressure Sodium or Metal Halide. What type of lights you use is a matter of personal preference and budget. LEDs are costly to set up, but not to run over time. HID lights are less costly to buy initially, but electricity costs can get high. They also get very hot and need adequate ventilation, and carry a risk of fire or burns. In addition to lights, most domestic growers use a 4’x4’ grow tent and use fans to ensure good air circulation and reflectors to maximize light. Setting up an indoor grow can be costly, but it can also provide you with 4 or 5 harvests a year, which may pay for itself quickly, depending on your cannabis needs. An indoor plant, grown with skill under lights, will produce around 10 ounces/plant of cured cannabis.

When you grow cannabis indoors, you are able to control the light, humidity and temperature. Most indoor growers have the lights on for 18 hours/day during the vegetative stage and when they are ready to bring them into flower they switch the timer to 12 hours/day of light and 12 of darkness.

Any plant grown indoors will rely on you entirely for nutrients and water. Typically they are grown in a sterile potting mix, so they’ll starve if you don’t feed them.

Bees and Cannabis

You may see ‘Cannabis Honey’ for sale. The CBD or THC will have been added to the honey by the producer–not by the bees.

Cannabis is wind pollinated, not insect pollinated–that means the plants have not evolved to not be attractive to bees or pollinators. They don’t have nectar and their flowers aren’t showy and, since male plants are rogued out, there is no pollen on offer either. Having said that, hemp–a relative of Cannabis–is very attractive to many pollinators and hemp pollen provides a source of proteins, fats and minerals that bees need to raise their young. Hemp farmers grow both male and female plants, since they don’t have the same concerns as those who grow cannabis for medicinal or recreational use.

Breeding pollination remove powdery mildew on cannabis seeds

Humans make use of the possibilities of nature

The goal of plant breeding is to generate plants with improved characteristics. The basis of classical plant breeding is the selection of plants with desired features and their targeted crossing with each other. In plant crossing, the characteristics of plants – both good and bad – are recombined. For this reason, repeated crosses with subsequent new rounds of selection are necessary in order to bring together the advantageous characteristics and, ideally, to exclude the negative ones. The diversity of features within a plant species is of critical importance for reaching the diverse breeding goals.

The likelihood of reaching the desired breeding goal increases with the genetic diversity that can be chosen from. Plants with the desired constellation of characteristics are propagated and, after different tests, reach the market as a new variety.

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Where do our cultivated plants come from?

A story spanning thousands of years

At the end of the stone age, humans cleared the forests that were typical for the landscape of Central Europe and selected particular plants for cultivation in these areas. In this way, the natural species composition changed, and farmland and meadows were formed.

For further cultivation, humans chose those plants among the cultivated plant varieties that possessed the most favorable properties with respect to their needs. In this way, individual plants with, for example, longer ears or larger fruits were chosen for further cultivation. This led not only to an increase in the number of productive plants but also to an increase in the amount of their genetic material in the stock. As a result, the genetic composition within the cultivated varieties was altered.

Many of our cultivated plants were already formed from wild varieties by human intervention in this way thousands of years ago. The grain varieties that we know today were formed from wild grasses. Our main varieties of grain, wheat, barley, and rye, but also maize, potatoes, and tomatoes were brought to Europe from other regions of the world.

Why do we need plant breeding in the first place?

The aims of plants are not those of humans

The properties that are advantageous to plants in nature are those that improve their capacity to adapt to the environment and increase their competitive power (Ask the Plum). Properties that ensure the survival of the plant, may, however, interfere with or even completely prevent human use: for example, the early shedding of seeds or the production of bitter or poisonous substances for protection against enemies.

The example of wheat makes this clear: At the beginning of the cultivation of wheat, humans chose plants for cultivation whose seeds remained on the ears for as long as possible and did not fall out prematurely on the field or get lost during transport. In this way, humans obtained higher yields, but at the same time limited the fertility of the plant. That’s why wheat must be threshed so that the grain (the seeds) are released.

Almost none of our modern-day agricultural crops can survive outside of cultivated fields, as they have high demands on the soil as well as sizable nutritional demands, and what is more they are less competitive with respect to wild plants.

What are the objectives of breeding?

The aims of humans are not those of plants

For every type of cultivated plant there are specific breeding aims. These breeding aims are related to:

  • Yield
  • Yield stability (e.g., stability, resistance against pests and disease, higher tolerance of climatic influences)
  • Improvement in quality (Composition with regards to healthiness, taste, or processing characteristics)
  • Adaptation of plants to production processes (e.g., even ripening, uniform neck length)
  • Better utilization of resources (nutrients, water, etc.)

What are plant characteristics based on?

The genes of the parents determine the characteristics of the children

The basis for the characteristics of plants is the information that is saved in the form of genes in the nuclei of plants on DNA (Ask the Grape, Part 1). The expression of characteristics may be determined by one single gene or by many genes together.

Plants can contain from approximately 30,000 (thale cress) up to more than 60,000 genes (wheat). At fertilization, the genes from mother and father are recombined, resulting in progeny with a new composition of characteristics (Ask the Grape, Part 1). The greater the diversity within a given species, the more possibilities there are for combination. The task of the breeder is to select the best candidates for further breeding from this diversity. This is particularly difficult for characteristics that are not immediately apparent, such as taste or resistance to specific diseases.

How do plants actually reproduce?

Of blossoms and clones, bees, and wind

Typical self-pollinator are wheat, barley, oat, rice, peas and beans.

Reproduction in plants takes place either sexually via pollination and fertilization or asexually via vegetative reproduction.

In sexual reproduction, pollen and egg cells are formed in the blossoms of flowers. A distinction is made between self-pollination, in which the pollen of one blossom reaches the stigma of the same blossom, and cross-pollination, in which the pollen from the blossom of one plant is transferred to the stigma of another plant.

The type of pollination has a decisive influence on the composition of characteristics in the progeny and also on their diversity.

As seeds and pollen come from one and the same plant in cross-pollinators, the progeny is mostly identical, among themselves, as well as compared to the parental plant. The hereditary material in these plants can only be altered through mutation or cross-pollination.

Typical cross-pollinator are rye, lucerne, sunflower, rape, cannabis, carrots, sugar beets and corn.

In cross-pollination, the pollen and egg cell originate from different plants. The pollen can be transported by insects or by the wind to the recipient plants. The progeny from such a cross are composed of a large number of genetically different plants.

In addition to sexual reproduction, plants also have the ability to engage in asexual reproduction. In this process, so-called vegetative reproduction gives rise to plants that possess exactly the same properties as the original plant. Such plants are termed offsets or clones. Examples of plants that engage in this type of reproduction include potatoes and strawberries. Depending on the type of reproduction and pollination, different breeding methods have been developed.

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Which breeding methods are there?

Powdery mildew resistance of barley: Cross breeding of the ethiopian landrace (left) made the european elite cultivar (right) resistant against powdery mildew (as of ca. 1930).

Different paths lead to the same goal

Worldwide, about one third of harvests are lost due to plant diseases, pests, and weeds. Furthermore, future challenges will be enormous: the world’s population is constantly growing, while at the same time cultivation area is decreasing, and climatic conditions are changing. To ensure that in the future yields are of sufficient size and quality as well as being environmentally friendly, we need efficient and innovative plant breeding.

In the last century, the classical methods of plant breeding, based on selection and crossing, were supplemented with new practices. Techniques that facilitate the detection of plants that are suitable for further breeding, or techniques that enable the addition of individual traits have made plant breeding more effective.

The foundations for these techniques were laid by fundamental research on plants.

Classical methods

Selective breeding is the oldest form of breeding. First, mass selection was carried out, which led to the cultivation of improved mixtures of a plant species. Later, the best individual plants were selected from these mixtures (local varieties). In this way, the local varieties were broken down into genetically uniform lines (landraces).

Combination breeding is the crossing of plants with the aim of recombining features. In this type of breeding, different varieties of one cultivated plant may be crossed with each other or wild varieties are crossed into the cultivated plant.

Only the promising progeny are selected from the individual crosses. Self-fertilizing plants must be prevented from self-pollination in order to be able to generate new combinations (artificial crosses), while cross-pollinating plants are specifically crossed with other partners.

Hybrid breeding is an extension of combination breeding. Two genetically different, but homozygous parental plants (inbred lines), are crossed with each other. The progeny of this cross are far superior to their parents in growth and yield. This phenomenon is called heterosis. The crop of a hybrid variety cannot be used as seed purely for economic reasons, because in the next generation the heterosis effect and with it the high yield is lost through the segregation of characteristics.

Many tests have to be carried out before a complete variety is obtained. From the first cross to the approval of a variety about 12 to 15 years are required.

Next to corn, hybrid breeding is used in sugar beet, sunflower, different vegetables, cereals as wheat and rye and in ornamental plants.

New, supplementary methods

In marker-assisted breeding, molecular techniques like PCR, sequencing or compositional analysis (Ask the Grape, Part 2 – coming soon) are used, in order to investigate the genetic composition of the progeny of crosses and to compare them with the source plants. The creation of such a “genetic fingerprint” allows, already in young plants, determination of those which are suitable for further breeding. The time required for breeding efforts is shortened.

Smart Breeding: After starting a crossbreed, molecular biological methods are used to select progeny with favorable new characteristics. Those are used for continuous breeding, until all undesirable characteristics are removed.

Smart Breeding: After starting a crossbreed, molecular biological methods are used to select progeny with favorable new characteristics. Those are used for continuous breeding, until all undesirable characteristics are removed.

Smart Breeding is a “refinement” of marker-assisted breeding. This method, also known as precision breeding, allows interesting gene variations or wild plants to be used more systematically and more effectively for breeding than was possible in the past.

While mutation breeding alters the genetic material in an undirected way through radiation or chemicals, and, in this way, influences the composition of plant properties only in random and haphazard ways, genetic engineering involves the targeted insertion of one or more genes that give rise to new properties. This insertion can cross species boundaries (transgenic plant) but can also take place within a given plant species (cisgenic plant).

Why do we need gene banks?

Securing the diversity of features

The gene bank Gatersleben stores ca. 145.000 seed samples of crop plants from all over the world. For example, 20.000 different barleys are stored in the gene bank.

As breeding involves the constant selection of plants, it can lead to a narrowing of the gene pool within a plant species. This narrowing is particularly serious, when at the beginning of the use of a plant species by humans, only a few varieties were domesticated and used for further breeding.

When breeders and scientists realized this, gene banks were developed, in which the genetic diversity of plants in the form of seeds is gathered and preserved. Through the use of the new and more effective breeding methods, the use of old and wild varieties stored in the banks will in the future increase and the gene banks will gain in importance.