In order to choose the fertiliser that best suits our needs, or to be able to compare our choice with similar products, it is important for us as growers to know the full range of nutritional elements in a particular fertiliser.For this we consult the product label, where we find information on the proportions of nitrogen, phosphorus and potassium (the NPK or N-P-K).

For this we consult the product label, where we find information on the proportions of nitrogen, phosphorus and potassium (the NPK or N-P-K).
However, sometimes we have discovered that while the label on fertiliser X shows NPK ratios ten times greater than those of fertiliser Y, the amount of each to be added per litre of water is exactly the same. This happens because the NPK proportions that we are comparing sometimes use different systems of measurement.

DIFFERENT WAYS TO express the amount of nutrient

There are many ways of describing the amount of nutrients in liquid fertilisers. The NPK level in a liquid fertiliser can be referred to without taking into account the water in which it is diluted. In other words, the idea is to identify each nutrient proportionally with respect to all the elements in the fertiliser. For example, a fertilizer classified as 26-23-29 has a nitrogen content corresponding to 26% of all the elements in that particular mix. As you can see, this representation of the concentration levels is characterised by very high numbers.

Another option is to express NPK levels in terms of presence per unit of volume. A 3-3-2 liquid fertiliser, for example, is one with 3 grams of nitrogen per 100 ml of fluid. This system is referred to as weight/volume (w/v), a method that calculates only the volume into which the fertiliser substances are dissolved rather than the weight they add to the solution.

A third alternative is based on the amount of NPK present in a liquid fertiliser, a system known as weight/weight (w/w). We know that a litre of water weighs 1 kilogram, and after we mix in the liquid fertilizer components, the resulting weight is that of the water plus the weight of fertilising elements and other products, including humic acid, buffer materials etc. The result: a litre of liquid fertiliser will always weigh more than 1 kilogram. The number of grams of dissolved solids per litre of water is what we call density. A density of 1 applies to water in which nothing has been dissolved (distilled water, for example). The more solids we dissolve, the greater the density. For example, a 2-2-1 label on a litre of fluid fertiliser weighing 1.2 kilograms indicates that in every 100 grams of liquid there are 2 grams of nitrogen. Multiplied by the density, the result is the concentration expressed in terms of w/v (as explained in the previous paragraph). This explains why we cannot jump to conclusions about which fertiliser is more concentrated, even when labels on two products present equal NPK ratios, as concentration is determined by density. The first conclusion we can reach is that the ratio numbers expressed as w/v are larger than those expressed as w/w.

In order to supply sufficient nutrition to plants using two fertilisers marked with w/w NPK ratios (the expression of their concentration), the amount in millilitres to be added from each one can be determined in the following ways:

- If the density of the product is known, all we have to do is multiply this figure by the given w/w proportions and we will have the ratio expressed in w/v. This also
tells us how many grams of nutrients there are per millilitre.

I want to use a 2-2-1 fertiliser with a density of 1.2 g/ml to reach a level of 100 mg/l of nitrogen in the solution that I will use to water my plants. To obtain that, I multiply the ratio by the density: 2g/100g x 1.2 g/ml = 0.024 g/ml = 24 mg/ml. This leads us to the w/v concentration, that is, we now know that our litre bottle of fertiliser contains 24 grams of nitrogen. If I want the nutrient solution for my plants to contain 100 mg, I need to obtain this amount of nitrogen (100 mg) from the bottle of fertilizer concentrate. Knowing that a litre of concentrate contains 24g nitrogen, we can rely on a general rule to determine how many millilitres I should add to a litre of water. Still using the same example, if one millilitre of nutrient contains 24 mg (0.024 g) of nitrogen, 100 mg will be obtained in 100/24 = 4.1 ml. To end up with the product I want to use on my plants, a liquid fertiliser with 100 mg of nitrogen, I should dissolve 4.1 ml of fertilizer concentrate in a litre of water. The NPK ratio in this example shows us that we will also be adding 100 mg of phosphate and half that much (50 mg) potassium.

- If the density of the liquid fertiliser product is unknown, we have several options. A densimeter can be used to determine density, or we can weigh a litre of the product. If we still cannot determine the density, there is another possibility on the label of the concentrate, where, in general, manufacturers provide indications for the amount of fertiliser concentrate recommended per litre.

As you will have seen by now, these methods merely serve to illustrate, and they lack precision, some more than others. The only way to obtain more accurate and reliable information on the total quantity of nutrients we are adding to the water for our plants is to measure the electrical conductivity, or EC. It is important to point out that organic manure or soil additives contain organic nutrients or trace elements, vital to our calculations, but which escape detection by the EC meter. In general, this means that if you also use soil additives in the care of your plants, the concentrate’s EC should be slightly lower than that of mineral soil additives or fertilisers.

CONCENTRATION DEPENDS ON DENSITY

With all of the above information in mind, we can draw the following conclusions: the w/w ratio represents lower amounts than those of the w/v ratio. For this reason, if we are going to compare two fertilisers, the first thing we have to do is to take note of the measuring system used for representing the nutrients. But even so, the w/w ratio does not provide exact information on the concentration, as this depends on density. In order to determine which fertiliser is more concentrated, following the manufacturer’s instructions on the required dose helps to give us an idea, if density and w/v are unknown. The best indication is given by dissolving equal amounts of both concentrates in a litre of water and measuring the mixes to find the highest level of electrical conductivity.

.
.
.
.
Reproduced with the kind permission from Canna-UK

The most reliable method for measuring the nutrient levels in Coco is using the 1:1.5 extraction method. EC and pH of the root environment can be determined by using this method. The pH and EC of the drain water generally deviates from the actual root situation, as Coco is able to retain and release elements.

1. Take a sample of Coco from the slabs or pots (photo 1). This can be done with a soil core sampler or a trowel.
   To get a representative sample the Coco must be collected from as many places as possible.
2. Put the sample in a bowl and determine whether it contains the right amount of moisture. The Coco has the right amount of moisture if moisture drains between your fingers when you squeeze it (photo 2). Add de-mineralised water if necessary and mix with the Coco.
3. Take a 250 ml measuring jug and fill it with 150 ml of de-mineralised water. Add Coco to the 250 ml mark (photo 3). Fully mix and allow the slurry to settle for at least two hours.
4. Mix again and measure the pH.
5. Filter this material and measure the EC.

It is advisable to perform a 1:1.5 analysis after 3 to 4 weeks. The target values for EC are between 1.1 and 1.3, for the pH, between 5.3 and 6.2. Very high EC values increase the risk of burning symptoms. To limit the risk of burning symptoms, the Coco can be rinsed with acidified water (pH 5.8: acidify with CANNA pH-GROW)

.

.

.

.

.

.

.

.

Reproduced with kind permission from Canna-UK

This predatory mite feeds only on spider mites. It should be the first choice for biological control of spider mites if conditions are suitable. Phytoseiulus is effective if released in sufficient numbers at the first sign of the pest, and if temperatures reach 20°C for at least a few hours each day. Optimum temperatures for control of spider mites are 15-25°C, when the predator breeds faster than its prey. However, P. persimilis is less effective in the hot, dry conditions (above 30°C and below 60% relative humidity) that favour its spider mite prey. The adult predators are slightly larger than the Two-spotted spider mite (Red Spider Mite)  and are orange-red and shiny. They have longer legs than spider mites and are very active, running around the leaves searching for prey. P. persimilis will eat both mobile stages of the Two-spotted spider mite (Red Spider Mite) and their eggs. Younger predators are smaller and paler than the adults. The eggs are pale pink, oval and about twice the size of those of the Two-spotted spider mite (Red Spider Mite). These can easily be seen with a hand lens when monitoring, on leaves with spider mite damage, and are a good sign that the predators are establishing. As the predators do not have wings they cannot fly, but they will move readily from plant to plant if these are touching. The predators are supplied in bottles with a bran or vermiculite carrier that is sprinkled on the plants. Products with larger numbers of predators in smaller amounts of carrier leave less carrier on the plants, deliver more accurate numbers of predators and allow more effective use of high doses in spider mite ‘hotspots’.

Now known as the Two-spotted spider mite (Tetranychus urticae)
Although serious problems are uncommon on herb crops, the damage caused by their feeding can make fresh cut and potted herbs unmarketable.

Identification

All stages of two-spotted spider mite  are usually found on leaf undersides. The young mites and summer adults are up to 0.5 mm long, light green in colour, with two darker lateral marks on their backs. In September or October, in response to shortening day length and cooler temperatures, and also earlier in the year in heavy infestations when plants are senescing, adult females turn a brick-red colour. The brick-red females that appear in the autumn find a sheltered place in the structure of the glasshouse or tunnel, or in plant debris, to hibernate. Over-wintered adults become active again in the spring, in response to increasing temperature and daylength. They move onto host plants , where they feed and lay small, clear, round eggs on leaf undersides. The eggs hatch into 6-legged larval mites, that feed on the leaves and develop through two 8-legged nymphal stages into adults.

Symptoms

Spider mites feed by extracting cell contents using their needle-like mouthparts. This damage causes fine yellow speckling to be visible on the leaves, which later develops into yellow or necrotic patches, making the plants unmarketable (Fig.3). In severe attacks, leaves or plants can senesce and the mites can produce extensive webbing.

Sources of spider mite infestation and favourable conditions

The source of the pest is usually overwintered females that hibernate in the glasshouse or tunnel structure and migrate onto susceptible plants in the spring. The pest can also be brought in on infested plant material. Spider mites have no wings so they cannot fly. However, they can walk from plant to plant, or along glasshouse, tunnel structures or inside grow tents. They can also spin fine threads of silk which allow them to be carried on air currents. Spider mites can also be spread on people or clothing. Hot, dry conditions favour the pest and allow it to breed rapidly. Many generations per season can occur, and on nurseries growing all-year-round herbs with heat and light during the winter, the pest can continue to breed throughout the year.

How to avoid spider mites and other infestation

• Check all incoming plant material for damage symptoms, particularly highly susceptible herbs.
• Use a thorough clean-up procedure at the end of each crop. Dispose of unwanted and heavily-infested plants and plant debris promptly and carefully, and clean bench, tent or floor coverings.
• Avoid moving people or equipment from infested plants to ‘clean’ plants on the nursery, and wash hands after handling infested plants.
• Maintain good ventilation
• Misting infested plants with water, if practical, can reduce spider mite population growth during hot, dry weather.

Before starting to grow indoors you really do need to think about what you want and above all about what’s possible.

How to start

Before starting to grow indoors you really do need to think about what you want and above all about what’s possible. Things you need to think about include how much to invest in plant materials and cultivation equipment such as plant food, lamps and ventilation.

Do you want to grow indoors or outdoors? Which plant/variety do you want to use and what kind of yields/crop do you have in mind? What stock material are you going to use? How much space do you have available for the crop? How many plants per square metre? Which growing medium are you going to use?

So there are quite a few points you need to watch and they’re all interconnected. Give it a bit of thought so that whatever you choose will be more realistic and there’s a better chance you won’t find yourself stuck with unpleasant surprises.

Seeds

You generally buy seeds if you decide you want to select a mother plant that you will then take cuttings off yourself. You need to make sure you choose healthy seeds.

Some seeds you can buy are what you call hybrid seeds. Hybrids are a cross between a number of varieties of the same crop . If these hybrids then get cross-bred again, you often get plants you can’t get a decent crop out of.

There are a number of ways of getting seeds to germinate, but you’re best off doing that indoors because that’s where the environment is better protected. A seed needs to absorb water before it can germinate. Then biological processes get to work inside the seed and it comes, as it were, to life.

One way of doing this is to put the seed in a glass of mineral water (If seeds are large enough). When a root tip starts to sprout put the seed on a piece of damp kitchen paper. How long it takes before the seed starts to sprout varies per variety and depends on the age of the seed.

Always make sure that the seeds are well ventilated. This helps prevent fungus. After a day the seeds are ready to be placed in their growing medium. Place them 2,5 times the seed height under the surface (e.g. If seed is 2mm place 5mm under the surface). Make sure the humidity is sufficiently high, but remember too that the area around the seeds mustn’t be too damp. So go easy on the watering.

When the first real leaves appear on your plants you can start giving some fertiliser. The fertiliser concentration mustn’t be too high: don’t go beyond an EC level of 1.2, depending on the hardness or EC of the water. Keep the temperature between 20°C and 25°C. Ideal humidity at this stage is between 60% and 70%.

As well as fertiliser, the light spectrum given out by your grow lamps also has a considerable influence on the way your plants grow. The blue part of the spectrum is what gets the plants to grow widthways rather than lengthways. This allows you to get robust plants before they start to flower. We call it pregrowing if you start growing plants in one area before moving them into another to flower. Again, this encourages robust plants that pick up strength faster and that can be readied for flowering straight away. Other advantages include less wastage and more frequent harvesting. You normally use fluorescent lighting in the pregrowing stage. This light is easy and inexpensive and a further advantage is that the lamps can be set close to the plants so you don’t need much room or any expensive arrangements like vents to draw off the air.

The reflectors for your lighting get dirty as time goes by. Clean them regularly. Research shows that light yields drop by 20% pretty quickly!

Cuttings

Buying cuttings instead of seeds has a number of advantages. First of all the plants have already grown a bit, which means that they’re not just stronger but you can harvest them earlier. You’ll also know more about your plant, because genetically it’s identical to the mother plant from which the cutting has been taken.

If you have a good mother plant of your own you can take cuttings yourself. Take cuttings from young, vigorous parts of the plant. Cut a piece off that’s between 5 cm and 15 cm long just above an axillary bud where the stem is between 2 mm and 5 mm thick.

The cutting shouldn’t have too much leaf because otherwise it’ll dry out too quickly – it can’t absorb water easily without roots. Remove any excessively large leaves so that the cutting looks like a small plant.

articles-growingdummies_text_2Cut the stalk diagonally. Try to maximise the area of the cut. If you’re not transferring the cutting straightaway to the growing medium it’s a good idea to put it in a glass of water. It won’t dehydrate but you’ll also ensure that air bubbles don’t get sucked up the stalk which will block the passage of the sap. Dip the end of the cutting in rooting powder/liquid and make sure to get rid off any excess. Ensure that the growing medium is nice and damp. Place the growing medium in a closed off area, a seed box say, and start giving it some water as a fine spray. Make sure you don’t keep humidity constantly too high.

After a week or two the first little roots start appearing. The cuttings have now turned into little plants and are ready to be transferred to another medium with more space for growth.

Sexing plants

Some plants have different male and female plants, like the hops you need for brewing your own beer . If you’ve grown a healthy plant from seed but you’re not sure whether it’s male or female, you can take a cutting to find out. Place the cutting apart and force it to flower by reducing the hours of light from 18 to 12 each day. See if it will start to flower!

Growth

When your plant has thrown out enough roots it starts to grow. A plant grows because the cells in the growth areas divide and because the cells that have already been formed, swell up with water. The plant is now using a lot of water and nutrients, above all nitrogen. In order to make the best use of these nutrients and the water the plant requires a lot of light.

Although the plant continues to grow when it comes into bloom, many growers get their plants to go through a pregrowing phase first. The longer this period lasts, the longer it takes before any harvesting. But on the other hand the plant has so much more time to develop branches, this increases its resistance to disease and defects, and also it can provide a bigger crop later. Allowing your plants a one week pregrowing phase will make them strong and robust.

Flowering

Even before there’s anything visible on the outside of the plant, at a certain point a switch starts to take effect within the plant. This is the switch that marks the start of the flowering phase; the first cells are formed that later make up the flowers. In annual plants this switch is activated by the days growing shorter. If you’re growing indoors you can decide yourself when the switch will happen by reducing the hours of light to 12. Light that is more to the red end of the spectrum, such as light from sodium lamps, influences this switch and stimulates longitudinal growth and root development. These lamps need to be suspended at a greater distance from the plants because they give out more heat. Many growers use combinations of lamps. During this period you need to make sure the plant remains undisturbed when in the dark period because this will extend the flowering period.

It is a good idea to keep the humidity (around the heads) at below 60% to prevent fungi such as Botrytis taking hold in the fruits or flowers. But it’s best to keep it above 50% to avoid spider mite.

Now that the plant has moved into the flowering phase (which lasts for at least 2 months), the plant’s nutritional requirements change. Its need for nitrogen (N), which was the primary nutrient during the growing phase, comes down but its need for potassium (K) and phosphorus (P) rises markedly. Stop giving fertiliser between 1 and 2 weeks before the harvest, as the plant’s ripening process nears completion.

It’s important that the young flowers do not get fertilised so that no seeds get formed. Plants have a tendency to put all their energy into the seeds, so they can procreate of course.

Remove flowers in the shade because these are virtually worthless, they just siphon off energy from the main crop. But never remove any leaves that are shaded. These generate the energy the heads need for their development.

When your crop is ready for harvest depends on the crop grown. Often crops are harvested too early. Affecting yield, taste and flavours!

.

.

.

Reproduced with kind permission from Canna-UK