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The A-Z Of Propagators

If you love growing plants from seeds or cuttings then a propagator is a must. With so many types of the market we’ve written this A-Z Guide to explain about the different types available and their features.

Aeroponic Propagators have been developed to allow you to grow plants in air. Aeroponics has long been recognised as one of the most productive ways of growing, with cuttings rooting faster, healthier and more successfully than other traditional methods of propagation. The reason aeroponics is so successful is that it allows the rooting zone to be fully oxygenated – an oxygen rich environment results in faster root development. Plus, aeroponics is more economical as it enables you to use less water, less nutrients and less growing medium. Aeroponic propagators are designed to hold your cuttings in place, so that the base of the cutting can be periodically misted with a fine nutrient solution. Typically this is achieved by having a submerged pump in the base section of the propagator which drives nutrient solution into low pressure misters directed at your cuttings. 

Blankets and Mats are an alternative to traditional propagators and allow the gardener greater flexibility, especially if space is limited. Unlike traditional propagators which will take up the same amount of space all year round, Electric Blankets and Warming Mats have been designed so that they can be rolled up and stored away when not in use – so taking up very little space out of season. Whether you buy a blanket or mat the general principle is the same – it’s just that we use the word ‘blanket’ when we are discussing larger sized heating mats. The blanket/mat is a waterproof flexible mat with a heating element inside. Once plugged into mains electric the mat will heat up to provide a base heat to anything placed on top of it – so you can place seed trays or pots directly onto the mat. The heat generated by the mat is designed to encourage rapid, strong growth of plants from seeds or cuttings. Although many plants can be grown without this base heat, a blanket/mat will speed up the germination process and for some plants which require high temperatures to germinate using a blanket/mat of this type will increase germination success. You’ll find a wide range of sizes of blankets/mats available to purchase – select the size to suit your requirements – don’t buy a huge blanket if you only raise a few seeds each year as you will only be wasting heat and electric. However, if you raise a wide variety or a large number of plants from seeds or cuttings then a blanket is more economical than purchasing multiple smaller mats.  

We’re often asked if a normal, household electric blanket would be suitable for use when growing plants from seeds or cuttings. The answer is a definite NO! Your normal, domestic electric blanket has not been designed to be on and working 24/7 and they have not been built to work in potentially wet environments. We only recommend that you use a blanket specially designed for the purpose of raising plants and no other type.

Cables designed to warm growing beds are often used by commercial growers as they need to heat huge propagation areas efficiently and economically. Also available to the domestic gardener in a range of sizes these soil warming cables are ideal if you have some DIY skills, as they enable you to construct large propagation benches at a fraction of the cost of heated blankets or mats.  The cables are mains operated, fully insulated, completely waterproof, very flexible, safe and easy to use. They can be used with or without a thermostat – although we always recommend a thermostat is used as this enables you to accurately control the temperature which the cable can generate. The cables are designed to provide a stable bottom heat when buried in sharp grit sand or fine gravel – so if you’re constructing a propagation area you would have the cable laid in sand or grit at the base of the bed followed by a layer of soil into which seeds or cuttings can be placed, or you can stand seed trays or pots directly onto the base layer. Providing maximum flexibility these cables can be used to provide heat in propagation benches and trays, in greenhouse borders and in cold frames. 

Dewpoint Cabinets are exclusive to Two Wests and Elliott who patented this sophisticated propagator now favoured by both commercial and domestic growers. The cabinet is based on the principle that air saturated with water vapour cools around the leaves of cuttings and plants. Moisture loss from leaves is eliminated encouraging healthy root growth, whilst the leaf surface remains dry preventing moulds. A completely self-contained unit, the cabinet efficiently creates the perfect conditions for easy, rapid propagation and growth of cuttings and germination of seeds by providing the three elements vital for successful propagation - light, heat and moisture – all at your control in an easy to operate unit. Trials have shown that the cabinet is suitable for most subjects and speeds up growth so much that rhododendron seedlings put on three years growth in just 9 months!   

Electric Propagators enable you to provide seeds and cuttings with one of the vital elements they need to germinate and grow – heat. Although in the past you might have been able to purchase propagators powdered by paraffin, if you want a heated propagator today then an electric powered propagator is your only option. By controlling the temperature where you sow your seeds or place your cuttings you are able to extend the growing season, speed up germination and enjoy bigger harvests.

Extended Growing – as you control the temperature seeds can be sown before the air temperature has reached the level required by the seeds – this means you can sow earlier in the year or out of season. 

Faster Germination – trials have shown that on average tomato and cucumber seeds germinate in 2 days in a heated propagator compared to 7-14 days when just on a sunny windowsill.

Bigger Harvests – if you grow your own vegetables, by starting them off earlier you can start to harvest sooner and you’ll be able to harvest for longer. 

You’ll also find that using an electric propagator is cost effective.  It’s not only cheaper to grow from seed than buying small plants, it’s also cheaper to run a propagator than having to heat a greenhouse to germination temperature and as germination is more reliable in a propagator less seeds and cuttings will be lost.

When buying a new electric propagator make sure you select one to suit the plants you intend to grow - important here is the germination temperature as you need to know that the propagator can reach the desired temperature and maintain that temperature for healthy seedling growth.

Fixed Temperature Propagators are designed to generate and maintain a factory set temperature – this is normally around 19*C (66*F) (check this when buying your propagator) as most seeds will germinate at a temperature between 18-22*C (64-72*F). The aim of these types of propagator is to reach this temperature as quickly as possible and then maintain that temperature by turning the built in heating element on and off as required. The heating element is usually within the base of the propagator and will be evenly spread across the whole area to avoid any hot or cold spots – you won’t be able to see this element as it is likely to be within a waterproof plastic casing. By providing a reliable heat which doesn’t fluctuate and can be maintained over a long period of time you should not only achieve greater germination success you should also be able to grow a greater range of plants than previously possible.  

Mist Propagation is recommended if your aim is to raise a lot of plants from cuttings. This is because a Mist Propagator provides cuttings with the perfect environment to enable them to root successfully. When a leafy cutting is taken it starts to wilt and die immediately because it has no roots to replenish its food and water, so to prevent it from dying you need to be able to get the cutting to form roots as quickly as possible. A Mist Propagator enables the cutting to quickly form roots due to the ‘mist’ it supplies. The mist will cover the leaves of the cutting with a thin film of water, so preventing wilting. At the same time this mist helps to control the surrounding temperature – so on really hot days when you may have needed to shade the cuttings the propagator can be left in full light. As the cutting is not deprived of light it enable it to make more food (via photosynthesis) than if requires for its’ immediate needs so this excess food is used to initiate the formation of roots. Of course, a Mist Propagator will have some form of base heat – usually using a soil warming cable – as, without heat the propagator would not be effective.

Natural Daylight can often drop below the desired level for optimum growth of cuttings, seedlings and young plants at exactly the time it’s most needed – early spring and late winter. This means that to boost natural daylight gardeners will need to use artificial lighting. To encourage maximum plant growth natural daylight needs to be supplemented in early morning and late afternoon – for example, in spring you would have artificial lighting switched on from 6am until 9am – then turned off between 9-3 when natural light will be sufficient – then turn lighting back on from 3pm until 7pm. To achieve this type of planned lighting it’s easy to have a timer to control turning on and off. However, you will need to have some manual control dependent on the weather – for example, if it’s overcast all day you might decide to have the lights turned on all day – from 6am till 7pm. If you don’t want to light your whole greenhouse or polytunnel, then a propagator with a built in light may be the answer – those with built in lights include our exclusive Dewpoint Cabinet (for gardening on a grand scale) and the smaller Grow Light Garden.

Propagation Frames or Propagation Beds enable the gardener with some DIY skills to build their own ‘propagator’.  You can construct a frame from timber to the exact size you require or you can purchase one of our propagation trays or benches (these come in standard sizes but are also available tailor made). Our propagation trays and benches are made from aluminium so should last a life time – timber made trays would need to be lined with polythene to extend their life and even then dampness will mean they start to rot after about 5 years. With these type of ‘propagators’ you would need to install a Soil Warming Cable to provide the heat – this should be laid on top of 2” of good quality coarse grit sand (also known as ‘sharp sand’), or a mixture of coarse grit sand and a capillary aggregate (such as perlite or perlag) – this 2” depth acts as an insulation layer in the bottom of the bed so directing the heat upwards towards your plants. For full details of how to install a soil warming cable refer to our instructions by clicking here. To control the temperature of the cable a thermostat should be added – for these propagation beds a rod thermostat is usually used however you could use any type of thermostat which has a sensor that can be pushed into the growing media within the bed.

Thermostatically Controlled Propagators are the ultimate in professional gardening gear. They enable precise temperature control, so that you can change the setting to suit the type of plants you are propagating and, as you are set the exact temperature required no energy is not wasted reaching temperatures that may be unnecessarily high to germinate your plants. You can divide thermostatically controlled propagators into two main types – those with built in thermostats and those with remote thermostats. Propagators with a built in thermostat have a dial to enable you to adjust the temperature and the temperature sensor is not visible, it is built in to the structure of the propagator. Propagators with a remote thermostat have a dial so that you can set the desired temperature and have a temperature sensor on the end of a flexible lead. This allows you to place the sensor in the most appropriate area to measure the temperature – this could be pushed into the compost in a seed tray or plant pot, or it could be rested amongst the plants etc etc. 

Unheated Propagators are the cheapest and most straight forward propagators to use. They are normally comprised of a seed tray and clear cover. The clear cover is intended to warm seeds sown in the seed tray by 5-8*C above the ambient or room temperature. Some clear covers will incorporate adjustable vents so that you can adjust this and affect the temperature within the cover and allow fresh air to your seedlings. When used within the home they will stop most fluctuations in temperature – unless your heating turns off at night. However, used in a greenhouse or polytunnel you will have very little control over the temperature (unless you intend to heat the greenhouse itself) and are not guaranteed to be frost-free. Examples of unheated propagators which we would recommend include the Compact Plant Trainer, the range of Propamatic Units, the Seed Success Kits and Rootrainer Sets with covers. These unheated propagators are ideal if you want to speed up the germination of hardy annuals or beans at very little cost (as no electricity is required).

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