Growers Tips: Using the Flood and Drain System

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flood and drain system

Think hydro is too complicated? How about a hydro system that lets you grow in pots, using any growing medium – even your favorite compost – and cuts down on your hard work? Our campaign for the fastest growth and the biggest yields continues, with a look at the flood and drain system and technique for growing weed!

NFT (nutrient film technique), a cultivation method that is classed as ‘pure’ hydroponics, is pretty simple to use, although it and other pure hydro styles of growing do tend to scare off a lot of gardeners. It’s understandable that they do not want to give up the security of having a growing medium – be it compost, cocos or clay – surrounding the roots of their precious plants, particularly when there are some tasty buds at risk! In this issue, we look at a hydroponic technique that offers faster growth cycles and bigger yields of active hydro but has the flexibility to be used with cocos or compost.

Ask yourself this question: when you first started growing, what technique did you use? I am guessing that at least 90% of you out there started out by hand-watering pots filled with compost. Fair enough, it is a great method for a beginner; compost is very forgiving and will buffer against pH fluctuations and over-feeding. Plus, hand-watering your plants every other day means you can concentrate on getting your environment right and, let’s not forget, you can achieve a shit-hot yield using compost!

But, what if I told you that there is a hydroponic technique out there that would have been great for your first grow – and all the grows that followed – where you could use compost and pots, reduce the amount of time you spend mixing feeds and watering AND shorten your growth cycle AND achieve bigger yields than hand-watering? Less work plus a quicker crop plus more buds at the end? Maybe you should have taken a look at flood and drain. Maybe it’s time to take a look now.

What is Flood and Drain?

The principle of flood and drain is simple. A plant sits on a table or in a bucket and nutrient solution is pumped in from a reservoir, flooding the table or bucket; when the pump turns off, the nutrient solution then drains away back into the reservoir. A timer is attached to the pump and is used to set the frequency of the flood and drain periods.

During the flood period, the roots of the plants are submerged, allowing them to take up all the water and nutrients they need. All stale air is then expelled from the root zone; as the solution drains away, fresh oxygen is pulled back into the root zone. As the plants grow larger, the number of floods per day is increased. The amount of nutrient solution used is easily measured and this allows experienced growers to tailor feeding schedules to get the optimum yields from their plants.

The flood and drain technique for growing weed really is one of the most flexible hydro methods ever, because there is something for everyone. At its most simple it can be a way to just keep your pots automatically watered, but for the more experienced grower, it is the method that offers the most amount of choice, as you can amend the number of flood periods per day (and how long each period lasts). This way you can tailor the system to your own growing environment – because every grow room has different humidity, temperature and airflow – and get the maximum yield from your plants.

Why Flood and Drain over Hand-watering Pots?

For several good reasons. Read through:

  • Plants grow faster and yield more: Plants take up more water and nutrients than they would with hand-watering; feeding little and often throughout the day is healthier than giving one large feed every other day.
  • The root zone is completely re-oxygenated several times a day: During the flood period, air is completely forced out of the root zone and fresh oxygen is pulled back in. Oxygenated roots mean a healthier plant that will grow faster and yield much more than a hand-watered plant.
  • Able to adjust the system: Allows experienced growers to set the perfect feeding conditions for their specific growing environment – plus the ability to set variable feedings on a timer means you can set the optimum feeding schedule for specific strains.
  • No buildup of nutrient salts: Any nutrient not used by the plants just drains back into the reservoir, instead of building up at the bottom of the pot. A buildup of nutrient salts will stunt growth, as it causes certain nutrients to be ‘locked out’.

Type of Systems: Flood and Drain Technique for Growing Weed

There are two styles of flood and drain system: the table system and the modular or bucket system. Both of them use the same technique and have their own sets of benefits.

Flood and Drain Table System

In a flood and drain table system, plants sit on a surface held above a nutrient solution reservoir. The table is usually flat, with drainage running to the center where there are two drainage fittings. One of the drainage fittings sits flush to the table – this is the inlet drain – the other will be around four inches above the bottom of the table – this is the overflow drain.

The inlet drain is attached to the pump and the overflow drain just runs back into the reservoir. When the pump is turned ON, the nutrient solution is pumped into the table through the inlet drain. Eventually, the level of nutrient solution will reach the level of the overflow drain and flow back into the reservoir. The overflow drain prevents the table from overflowing… just like the overflow drain in your bathtub! When the pump is turned OFF, the nutrient solution in the table drains back down the inlet drain, through the pump and back into the reservoir.

A timer is used to set the frequency at which nutrient solution is pumped from the tank to flood the table, and is then allowed to drain away. As the table floods, the plants take all the water and nutrients they need. All stale air is expelled from the root zone; then, as the solution drains away, fresh oxygen is pulled back into the root zone.

A major benefit of the flood and drain table system is that you can grow your plants in any growing medium – soil, clay, cocos, or mapito. You can grow in pots and move the pots around the table if you need to, or you can fill the whole tray full of clay pebbles and allow the roots of the plants to spread across the entire table – this is the method to go for if you are looking for the fastest growing and maximum yielding crop. Table systems are near enough to leak-proof: because the reservoir sits right underneath the table there is nowhere for the nutrient solution to leak to – perfect if you are growing in an apartment or an attic! They also come in sizes that are ideal for grow tents.

Modular or Bucket Flood and Drain System

Similar to the table system, this setup uses a timer to control the number of flood periods and benefits your plants by giving them doses of food and water throughout the day, combined with a highly oxygenated root zone. However, the main difference in the modular system is that each plant is placed in its own individual pot.

A supply tube runs from the bottom of each pot into a main control bucket, which in turn is connected to a main reservoir. The system uses gravity to send nutrient solution to the pots and only uses pumps to fill and drain the main control bucket, which has two magnetic float-valves mounted inside to control the power to the pumps (in both the main reservoir and the controller bucket). These floats control the flood level in the pots precisely, to stop any over-watering or flooding.

As the level of nutrient solution reaches a set level in the pots, the magnetic float valve in the main control bucket cuts the pump in the main reservoir OFF and turns a pump in the main control bucket ON. The pump in the main control bucket forces the nutrient solution out of the pots and back into the main reservoir.

The main benefits of the modular system are that you can space plants under lights however you like – so they can grow huge! Plus, the systems are easy to upgrade by just adding more pots, and you can run a big room full of plants from one single reservoir.

For which type of grower is Flood and Drain suitable?

As flood and drain systems are so flexible, they will benefit a real cross-section of growers:

  • New growers wanting to grow in pots and keep their workload simple by maintaining a number of plants from one tank, so they can concentrate on maintaining their grow room environments.
  • Experienced growers seeking an adjustable system to suit their individual growing environment and really maximize yield.
  • Personal growers after a smaller-scale system such as a flood and drain table that fits nicely into a three- or four square-foot tent, or one of the smaller modular flood and drain systems that are great for a two-lamp setup.
  • Large scale growers benefit from the modular flood and drain systems as they massively reduce the amount of time you spend watering your plants; they can be upgraded in size by just adding more pots. A smaller flood and drain table system can be used as a tidy vegging system to bring plants on under one or two lamps before transplanting to a large modular system.

Three Steps to Flood and Drain Heaven:

Keeping a dedicated flood diary is the key to massive growth and yields when using flood and drain. Write down the number of floods per day compared to the amount of solution needed to top up your system each day. The amount of solution that your plants use is directly related to their rate of growth – the idea is to maximize their consumption and maximize growth. By experimenting with the number and duration of floods, you will find the optimum number of floods for your growing environment.

Top up the reservoir depending upon the growing medium that you are using. If you are using clay pebbles, treat the flood and drain as a recirculating hydroponic system, and top up the tank every few days with half-strength nutrient solution. Use half-strength, because plants grown under powerful lights will take up water at a greater rate than they take up nutrients. Over time the EC (CF) of the solution will rise, so if you top up with a full-strength solution, you run the risk of overfeeding. If using an absorbent medium, like soil or cocos, the aim is to minimize runoff and top up the tank with full-strength nutrient solution.

When growing in soil or cocos, increase the number of flood periods by only one additional flood per day (for example, don’t jump from three periods to six as you are growing in an absorbent medium and can run the risk of water-logging the roots of your plants, or over-feeding them).

Increase the number of flood periods as your plants get older and increase in size. If you are growing with just clay pebbles and your young plants have just gone into the system, set the timer to two fifteen-minute flood periods per day. As the plants grow, increase the number of flood periods up to a maximum of one fifteen-minute feed per hour. You will need to perform a complete solution change every one to two weeks.

When growing in soil or cocos and young plants first go into the system, set the timer to just one fifteen-minute flood period per day. As the plants grow, increase the number of feeds up to a maximum of four fifteen-minute feeds per day. When using an absorbent growing medium, you should run the system to minimize runoff and usually only need to perform a complete nutrient solution change every two weeks, or when the level of solution is running low.

Q&A with a Flood and Drain Grower:

When can plants be transferred to a flood and drain system? If you have started your plants in rockwool cubes or small pots of soil or cocos, then ensure they are root-bound before you transfer them to a flood and drain system. You should be able to see lots of white roots on the outside of the starter medium.

If you are using a table system then you can veg and flower in the same system. If you are using the larger modular style flood and drain system then you may prefer to veg the plants under one or two lights before they go into the flower room, as your modular system will most likely be spaced under several lights.

How should the plants be spaced?

It depends on how many you want to grow and how big you want to grow them. Table-style systems are great for sea-of-green grows, where plants are spaced closely together and vegged until they form a low canopy. They are then switched to flowering for a ‘sea’ of buds!

The modular flood and drain systems are perfect for spacing out under several lights. You could choose to put four of the modular buckets under each light, or even just one bucket per light to grow some monsters! Modular flood and drain systems are tailor-made for growing big, big plants. I once saw a system in a twenty-lamp Californian grow room, where there were two plants per 1000-watt lamp, and each plant had been vegged for eight weeks before being switched to flower. It was like a room full of trees!

How high should EC be set?

If using an inert growing medium like clay pebbles, there is a very little buffer (or protection) against over-feeding, so make sure you start to feed at half of the nutrient manufacturer’s recommended dosage. If you are using soil, cocos, or a mixture of clay and cocos, then there is more of a buffer around the roots and you can start your plants at the nutrient manufacturer’s recommended dosage.

Will the Plants Need to be Supported?

Not necessarily. Unlike pure hydroponic techniques such as NFT or aeroponics, there will be a growing medium surrounding the roots, helping the plant to support itself. However, as with all types of indoor grows, if your plants are putting out some big buds you will want to support them and stop them from falling over.

So, whether you are a newbie or a green-fingered expert, flood and drain have something to offer. Give it a try – you won’t be disappointed and your plants will love you for it!


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