Passive Hydroponics

By: Soft Secrets, November 1, 2011

Let's face it, active hydro isn't for everyone; playing with pumps and feeding schedules, checking EC and pH may not be your cup of tea… and some of us like getting our hands dirty with soil!

Let's face it, active hydro isn't for everyone; playing with pumps and feeding schedules, checking EC and pH may not be your cup of tea… and some of us like getting our hands dirty with soil! But how about the benefits of hydro; more buds and less time spent watering your plants, without having to give up your beloved pots? Time to give passive hydro a second look…

What is passive hydro?

Passive hydroponics is the ‘catch all' term for growing technics that involve making nutrient solution constantly available to the roots of a plant. Unlike active hydro techniques, which employ a water or air pump to deliver nutrient solution, passive hydro techniques usually rely on the capillary action of the growing medium surrounding the roots, there is no pump involved. This is usually achieved by keeping the growing media in contact with a reservoir of nutrient solution, in its simplest form standing a pot of growing media in a saucer of nutrient solution is passive hydroponics.

Plants grown in a passive hydro set up will have constant access to water and food and, because most passive systems involve watering from underneath, the top part of the root zone remains highly oxygenated. Therefore, passive hydro can provide superior results compared to traditional hand watering methods. The more oxygen, water and nutrients that a plant can absorb, the bigger the yields they will produce.

For growers looking for a simple introduction to hydro or simply an increase in growth rates and yield compared to hand watering, but aren't ready for a ‘true' hydroponic set-up, passive hydro is the way forward.

Why passive hydro over hand watering pots?

• They're simple – for an inexperienced grower who is still learning the basics of cultivating indoors, passive hydro reduces the risk of over or under-watering and there are no pumps, timers or complicated feeding schedules to figure out.
• Increased yield – constant access to nutrient and water means healthy growth, bigger plants and more buds.
• Less work – looking for less maintenance? Passive hydro provides the perfect compromise between workload and yield. You'll pull less ounces than you usually would with an active hydroponic set up, but you'll certainly do less work for your bud.
• Easily expandable – most types of passive hydro systems that run off a header tank or reservoir are easily expandable without increasing your workload. This means it's as easy to water 200 plants as it is to water 20 plants!

Healthy plants grown in a passive pot and tray set up.

Types of passive hydro system

Trays and saucers – placing a pot of growing media in a saucer or tray is the simplest form of passive hydro. Plants can be watered from above using a watering can, the run-off fills the saucer and, as the plant feeds, the run-off will be absorbed into the pot via the capillary action of the media. The saucer acts as the reservoir and effectively decreases the number of waterings required – handy if you can't get to your plants every day.

Another method is to water from below, using a gardening tray as the reservoir – these are available in various sizes from any decent hydro shop. Pots are filled with an absorbent growing media – soil, coco, rock wool mini cubes – and placed in the tray. Nutrient solution is then poured into the tray and will be absorbed into the pots. It's a good idea to place a cover over the top of the tray (cut holes in it for the pots first) as this will prevent the nutrient solution from evaporating away under the hot grow lamps.

Saucers and trays are a simple and cheap way to reduce the amount of time you spend watering your plants, but do have their draw backs; keeping the growing medium wet all the time will mean there is less oxygen in the root zone, which can lead to root rot. It's important to allow the growing medium to dry out and become aerated between waterings.

Pots and trays – hand water and leave for days

Gravity fed – a similar watering technique to using pots and trays, these systems use a large reservoir or waterbutt to deliver nutrient solution to the tray in which the pot sits. The rate of flow of the solution is controlled by a valve that is either connected directly onto the reservoir or onto the tray itself. The solution flows through the valve and into the tray, where it is absorbed into the pot. The valve then stops the flow once the level of solution reaches a desired height in the tray.

The most popular of these systems is the Autopot which is a modular system that can be expanded from 1 pot to literally 1000's of pots! Depending on the size of the reservoir used, the system can be left for weeks. Ideal for large scale grows.

Hempy buckets – these are a great option for growers looking to cultivate big plants, they are also cheap to make and easy to maintain. To make one, you will need;
– A 20L black plastic bucket (important that it's black, as this will keep light out of the root zone and prevent algae from growing in the reservoir)
– A drill with a half inch drill bit
– A try to catch run-off
– A mix of 3 parts perlite and 1 part vermiculite
– Any decent hydroponic nutrient

Drill a hole on the side of the bucket, 2 inches from the base. Fill the bucket with the perlite / vermiculite mix and pot up your plant (the plant should be root bound in a propagation block). Water from above until you see run-off coming out of the hole on the side of the bucket. The base of the bucket is now the reservoir, effectively mimicking the water table that a plant feeds from when naturally growing outdoors.

For the first 2 weeks the plant will need to be watered every other day as its roots fill the bucket and head towards the reservoir at the bottom. Once the roots reach the reservoir, the growth is phenomenal! The watering is then reduced to twice a week, hand water the nutrient solution until you have achieved around 30% run-off, then you can be sure that you've replaced all the old nutrients in the reservoir and have drawn fresh oxygen into the root zone.

The hempy bucket offers the constant supply of nutrient, water and oxygen that leads to rapid growth and massive buds. When the roots hit that reservoir at the bottom of the bucket your plants will fly! The only downside is that planting up in a relatively large container from the start means a longer than usual veg period, so they're not so suitable if you're looking to get a quick crop in. But if you like the idea of big plants, give them a go.

The most popular passive hydro system – the Autopot

What type of grower is passive hydro good for?

Any grower looking to reduce their watering workload should at least take a look at passive hydro, for some growers it is a perfect match;
• Beginners or inexperienced growers – when starting out from fresh, there is so much to fuck up when growing indoors, that it makes sense to simplify the actual feeding of your plants! Using a passive set up with a reservoir turns watering into a weekly task, rather than a daily chore, so you can concentrate on mastering the basics of your grow room; lights, extraction and fighting the urge to trim off your first buds as soon as you spot them! Newbies scouting for a fail-safe system should look no further, passive hydro could be your saviour!
• Growers on a budget – cheapskates who don't want to splash out on their grow set up, can head to the local DIY shop and pick themselves up a set of 20L buckets and a couple of bags of perlite and vermiculite to create a hempy bucket set up for the same price as some quality pots and two bags of soil – and they'll most likely score a better yield!
• Commercial growers – when growing large scale commercial, it's all about getting maximum yield with minimal risk. To avoid getting caught with your hands dirty, you'll need to spend as little time in the grow room as possible. Hand watering large scale is a full time job, so that's a no-no. Active hydro systems will give you the yield, but maintenance duties will mean frequent trips to the grow room to top up the system and adjust EC and pH levels. A passive system fed by a large reservoir can, in theory, be visited once a week, massively reducing the risk of drawing the attention of the nosey neighbours, local law enforcement or dirty, crop stealing herberts!

The three steps to passive hydro heaven

1. Use a light and airy growing medium – passive set ups rely on the capillary action of the growing medium to transport food and water throughout the root zone. This means that the growing medium is wet for the majority of the time. To ensure that the roots remain oxygenated and healthy, choose a well aerated growing medium; coco is ideal as is a coco / clay pebble mix (like the 60/40 mix currently on the market), mix perlite into heavy soil mixes to increase the aeration or try a 50/50 perlite/vermiculite mix for an equal balance of aeration and water retention.
2. Choose your nutrients carefully – it may sound obvious but, when using a reservoir in a passive set-up, organic nutrients will spoil as quickly as they would in active hydro, possibly even quicker as there is no pump to agitate or oxygenate the solution. If your passive set up consists of watering from above and catching run off into pots and trays, then organic nutrients are fine. But if you're using a large reservoir to feed your crop, then choose mineral nutrients all the way. If using a very large reservoir then it's a good idea to fix a circulation pump at the base of the res and set it on a timer. This will effectively ‘mix' your solution, allowing you to leave the grow for longer periods without the worry of the nutrient settling.
3. Keep on top of your levels – when using a large reservoir, bear in mind that when plants first go into the system, they will use much less water than when they are mature and will take a longer time to empty the reservoir. Therefore, if you completely fill your reservoir when the plants are young, be prepared to add additional nutrients to the solution before it runs empty. Otherwise, you may notice your plants showing signs of under feeding as their food requirements increase, but the amount of nutrition in their feed remains the same.

A saucer under a pot acts as a simple reservoir

Q+A with a passive hydro grower

When can plants be transferred to the system?

As soon as they are root bound in their starter medium, you should see white roots on the outside of the block or pot. To avoid transplant shock, try and use the same starter medium as your main growing medium, e.g. a coco pellet if you're potting up into coco, or a rockwool cube if you're going into a hydro mix of perlite and vermiculite.

How should plants be spaced?

Depends entirely on how you want to grow and the amount of space you have, passive systems usually allow you to space the plants out however you want. Put them nice and close and flower them early for a sea of green or space them further apart and veg for longer if you want some monsters!

Will plants need to be supported?

The passive systems rely on having growing medium around the roots, so this is usually enough to support them. However, it really depends on how big you grow your plants! If you're going for a sea of green then you shouldn't need any extra support. I've always preferred growing bigger plants, so usually just use a bamboo cane and a simple tie, just the same as I did when I hand watered pots. Make sure you set up your supports before you flip to 12/12, when you can actually get in amongst your plants. Nothing worse than crawling through foliage and snapping off branches and stems as you go!

So, there you have it; want to cut down on your watering workload? Give passive hydro a go!

Happy growing!

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