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Flood & Drain Advice

IWS Flood & Drain Systems

Flood and drain is an irrigation technique that fills the pot with nutrient solution from the bottom. As the nutrient solution rises in the pot it forces out the air and saturates the growing media. As the nutrient solution drains from the pot, fresh air is pulled back into the growing media enriching it with oxygen - vital for healthy root growth. Frequent flooding and draining of the pot should occur in order to optimise the available oxygen in the root zone.

Here we will try to give you advice on all aspects of using the system, giving you a better chance of success.

Which Growing Mediums?

This common question really has with no correct answer as the growing media you choose to use often comes down to personal preference. Good results can be achieved with many different media’s and mixes but the key features you should look for in your media are:

  • Low-medium Water Holding Capacity (WHC)
  • High Air Filled Porosity (AFP)

Expanded Clay Pebbles

A growing media that is ideal for flood and drain without the need for anything to be added or mixed in is Jongkind Clay Pebbles. These pebbles carry the RHP stamp and are made specifically for horticulture; they have a high rate of water retention compared to most other clay pebbles. There is plenty of air space between the pebbles creating a high AFP.

They also are capable of absorbing and releasing nutrient solution from their porous structure. Clay pebbles can be flooded frequently with a low risk of over watering, which helps keep the root zone replenished with lots of oxygen and fresh nutrients.

Did you knowA 10L pot of dry clay pebbles can absorb up to 5L of water! This shows just how porous they actually are.

Coco / Clay Pebble Mix

It is also possible to use a mix Coir (Coco) with clay pebbles to increase the WHC. When mixing coir into clay pebbles it should make up 25-40% of the total volume of the growing media. Adding coir will allow more time between floods, meaning fewer floods each day.

Environmental considerations

As with any hydroponic system, your nutrient strength and irrigation should reflect your grow room environment. These hot and dry conditions will cause the plant to use more water and less nutrient. Consequently the nutrient strength should be set lower than usual to account for the nutrient strength rising in the pot.

In the same room during winter the room runs at 26°C with an RH of 60%, these more favourable conditions, that aren’t putting environmental pressures on the plants, will mean higher nutrient strengths can be used. It is therefore extremely important to consider the
effect that your grow room environment will have on your plants and adjust your feeding strategy accordingly.

 

Other Mixes

The IWS is very adaptable and can be run using many different growing mediums. Just remember to adopt a different flood time with each medium dependent on it’s water retention capacity.

Understanding The Flood Cycle

To get the best possible results from your IWS Flood and Drain system you must ensure you get the flood cycle right. The flood cycle is made up of 3 elements;

Flood Frequency -This is how often you flood the pot, which largely depends on what type of growing media you’re using and how well established your plants are.
  • Flood Height - This is how high the water goes up the pot. Generally we recommend you always flood to the maximum height.
  • Flood Duration – This is the total time of each flood and will depend on the size of your system and your choice of growing media.

These all play an important role together in getting the irrigation strategy as accurate as possible.

This guide can be followed for all growing media, not just clay pebbles, and should provide accurate flood times and optimum results.

When you have put the system together it’s time to get the growing media prepared.

Please note: No matter what growing media you use in your pots you must use 5-10cm (2-4 inches) of clay pebbles in the bottom of the inner pots. This will help prevent the bottom from holding too much water.

Wash the clay pebbles thoroughly to remove the dust and small particles; this can be done with tap water.

Insert the root control disk into your inner pot copper side up, add enough clay pebbles to cover the bottom of the pot, then add your chosen growing media on top. Only fill the pots three quarters full with your growing media at this point.

Now fill the reservoir with water and add nutrients to a suitable strength, this should be slightly higher (2 CF units, 0.2 EC) than your plants have been getting during propagation.

Finally adjust the pH in the nutrient tank to 5.5 - 6.5.

Setting The Flood Height

Now the nutrient solution is ready, turn on the timer and start a flood cycle. Make sure the feed-duration dial is turned all the way to the right for the longest possible flood time. The brain pot will start to fill and so will the pots. As the solution slowly fills the pots the growing media will take in the pH balanced nutrient solution preparing the growing media for planting.

Your aim here is for the maximum flood height to be the same as the amount of growing media in the pot. You should be able to see the water level rising to the surface of the growing media. Check by lightly pushing down on the media surface with the palm of your hand, this will make sure the media isn’t floating up. If the water rises over the surface of the growing media add more media until the level of the nutrient solution and the growing media is the same. When the brain stops filling and all the pots have the right amount of growing media and nutrient solution, leave them soaking in the nutrient solution for at least 1 hour.

After the pre-soak period, initiate the drain cycle on the timer by turning the duration dial to the left, this cancels the feed. Once the drain cycle is finished, check the pH and nutrient strength in the reservoir. The pH may have changed so adjust if necessary. If the pH or nutrient strength has changed dramatically, empty the reservoir and change the nutrient solution.

Now you need to get a stopwatch ready to time the flood cycle. Start the flood cycle and the stopwatch (you are timing how long it takes for the ALL THE POTS to fill back to the maximum flood height). As soon as the maximum flood height is reached in all the pots stop the stopwatch and start the drain cycle.

With the time recorded you can now set an accurate flood duration on your IWS system. If you are using clay pebbles, add 1-2 minutes onto the time recorded on your stopwatch. This short period at the end of the flood, in which the pots stay filled, helps to saturate the clay pebbles and purge the pebble’s inner core and outer shell of old nutrients. It will also allow the clay pebbles at the top of the pot to draw up water and nutrients by capillary action. It is not recommended that you hold your flood height for longer than 5 minutes as leaving your plants roots completely submerged in water for too long can cause poor root function and invite disease.

If you are using a mix with coco coir then the time recorded is your actual flood time. You do not need to add any extra time as your growing media has a fast capillary action and holds more water than pebbles alone.

Planting

Your pots should still be around three quarters full with the growing media at the same depth as the maximum flood height.

When it comes to planting your young plants you should plant them 1-2 cm into the growing media at the maximum flood height. This will mean that during a flood cycle the flood height will reach the bottom of the propagation block.

Please note: If you plant your young plants too deep in the pot your propagation block will become saturated causing poor initial root growth. Once you are happy with the planting depth, fill the rest of the pot with more prepared growing media.

Setting The Flood Frequency

How often you flood the pots will be determined by:

  • The growing media.
  • The plant size and water requirements.
  • The environmental conditions.

The Growing Media

If you are using a growing media that does not retain much water, such as clay pebbles, you will have to flood the pots with a higher frequency. When using clay pebble and coir mixes the WHC will be higher so flood frequency will be reduced.

Flood Frequency with Clay Pebbles

After conducting our own trials 8-16mm clay pebbles now come with our highest recommendation as the best growing media for flood and drain. We recommend using Grodan 3” or 4” blocks for preparing your plants to grow in clay pebbles.

When using clay pebbles you must use the IWS ‘Aqua Pots’, these are large net pots that allow better flooding and enhanced root development. To prevent roots from ‘chasing’ the water through the drain pipe, a copper root-control disk is used in the bottom.

During a flood cycle with clay pebbles the pots will fill and drain quickly, also between cycles the pebbles can’t hold onto large volumes of water. For this reason the flood frequency can reach a maximum of 1 flood every 2-3 hours when the plant is in full vigorous growth.

Your starting irrigation frequency depends on a number of factors; the size of your propagation block, the size of your plant and your grow room environment. Remember; your propagation environment will be quite different to your grow room environment, most growers find on moving their plants into their grow room their water demand will increase due to higher temperatures and lower relative humidity (RH). It is important to make sure the block and clay pebbles are not drying too much, or staying too wet, between irrigations.

When you can see a noticeable increase in vegetative growth you can increase the frequency to once every 3-4 hours. As the plants get bigger and their demand for water increases you should adjust the frequency to once every 3 hours but remember to leave the time it take to drain back before you feed again. I.E. if you want to feed every 3 hrs wait until your drain cycle has finished before counting down to your 3 hour feeds. A lot of growers leave this as their maximum flood frequency but some large plants in a hot and dry environment with a high water demand may benefit from a flood frequency of once an hour.

Remember that during each flood, water and nutrients are delivered to your plant and on each drain oxygen is pulled into the air spaces in the root zone. Therefore when plants have fully established within the clay pebbles; more frequent floods mean more fresh oxygen around the roots. Please note: if your plants are not well established within the clay pebbles they will not benefit from frequent floods.

Flood Frequency with Coir

When using coir and clay pebble mixes, you must use the IWS ‘Culture Pots’. These pots have a net base which has been designed specifically for finer growing media. The bottom portion of the net pot should be filled with just clay pebbles. The rest of the solid pot should be filled with your mix of coir and clay pebbles.

The key to using coir in flood and drain systems is to not over-water. For the first 1-2 weeks after planting, the establishment time, your pots will need irrigating a maximum of once a day. This flood should be in the middle of your light period. Some growers find they get better results by hand watering from the top of the pot every 1-2 days for the first week and go onto using the flood and drain irrigation cycle once they know the plants roots are well established and ready for regular irrigations. This is an excellent approach for establishing your plants, but understandably is sometimes impractical for growers with larger systems or for growers who run their light cycle during the night.

After the plants have established and vigorous vegetative growth has started, the plant’s water demand will increase. Around this time check the moisture level of your mix before the irrigation or toward the end of your light cycle, if it is drying you should increase your frequency to 2 times a day. The first and second irrigation should be equally spaced e.g. if your using an 18hr light cycle your irrigations should be at 6 and 12 hours.

These 2 irrigations are, in most cases, as much as they need, but plants that need to satisfy a high water demand may need irrigating 3 times a day during peak growth. An important phrase to remember when irrigating your coco coir and clay pebble mix is ‘transpiration before irrigation’, this means to wait for your plants to start using the remaining water in the growing media before giving them anymore. With this in mind you should have your first irrigation at least 1-2 hours after the lights turn on.

Hint: In most circumstances it is only necessary to flood the pots while the lights are on. Only during warm dark periods should you consider have 1 night time irrigation.

Environmental Considerations

As with any hydroponic system, your nutrient strength and irrigation should reflect your grow room environment. For example; if the growing media is clay pebbles and during summer the room runs at 31°C with an RH of 45%, these hot and dry conditions will cause the plant to use more water and less nutrient. Consequently the nutrient strength should be set lower than usual to account for the nutrient strength rising in the reservoir. In these conditions the pots should be flooded once an hour.

In the same room during winter the room runs at 26°C with an RH of 60%, these more favourable conditions, that aren’t putting environmental pressures on the plants, will mean higher nutrient strengths can be used and flood frequencies can be reduced to once every 2 - 3 hours. It is therefore extremely important to consider the effect that your grow room environment will have on your plants and adjust your feeding strategy accordingly.

Maintenance

Avoiding root blockages

Because the flood and drain system fills and empties through the same tube, roots growing out of the pot can sometimes cause blockages in the feed-pipe. To avoid this you should always use the copper root control disks provided. Also, if you can get in amongst your plants, routinely turn the inner pot round 45° in the same direction every 2-3 days. This will make sure roots stay away from the tube and may also produce a more even growth pattern.

Note. IWS are working on a new root filter which will eradicates any root blockages. You will have to slowly increase your fill times to allow the water to soak through any roots which have worked their way round the filter.

Checking for Root Blockages

If you suspect your pots or pipe-work may be blocked you can confirm it by quickly flooding the pot, do this by pouring 5-8L of nutrient solution in from the top of the pot. If the solution drains away freely it’s ok, if it sits there and takes a long time to drain you most likely have a blockage. Note: this technique only works well with clay pebbles. If your pot is blocked you should remove the inner pot and check the inlet/outlet tube for roots or debris.

Minimising System Problems

Most system problems come about through not keeping a clean system. You must make sure your float switches in the brain pot do not become dirty or clogged with any growing media. Each time you refill the reservoir a quick rinse with fresh water over the switches will help prevent problems. If you do notice sediment or debris in the reservoir or brain pot, remove or clean it immediately.



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