DIY Aquaponics - Vegetables for your Aquaponics System

Although we are going to focus on growing vegetables on this site nothing stops you from growing other types of plants as well. Most things grow well in a well tended aquaponics system but you should be carefull that you dont inadvertantly try to grow something toxic to your fish.

Our focus is on vegetables simply because the objective of this website is to show the reader how to grow good quality organic vegetables and fish in their own backyard and enjoy the long term savings and health benefits that food from an organic garden provides. As with hydroponics the best vegetables to grow in an aquaponics system are those that are leafy or bear fruit, root crops reportedly do not fare so well in some mediums though this is for the individual to decide and I advise you to experiment on a small scale if you feel the inclination.

The Grow Bed

The grow bed is a very critical part of your aquaponics system. Not only does it provide a place for your vegetables to grow but it performs the important task of biofiltration, providing a home for your bacteria colonies and ensuring that the excess nitrates are removed from the water that your fish live in. The vegetables themselves perform the final step in the process of removing the ammonia from your system. For in depth information on this process please consider reading our page on bacteria.

Ideally your growbed should be that same capacity as your fish tank though of course it does not need to be the same shape. So if you have a 500 litre fish tank then a 500 litre growbed is ideal. If your growbed holds more than your fish tank you might find that the fish are not creating enough ammonia for your bacteria to convert to nitrates and the vegetables may not be adequately nourished. For best results the grow bed should be at least 30cm (1 foot) deep as the bacteria that will inhabit the growbed prefer to be dark and well buried. Your growbed can be shallower than that but you will find that the system will not perform as well as it could. Fiberglass and heavy duty plastics seem to be the preferred materials for the growbed to be made from. You can use anything really within reason, even old bath tubs.

Your growbed is filled with some sort of hydroponic medium to provide a home for your bacteria and a place for your vegetables to anchor their roots. Those who were pondering why you would have a growbed of 500L and a tank of 500L should bear in mind that the medium will displace the water and depending on the particle size the growbed may only take 200L of water before flowing back to the tank, leaving your fish comfortable with 300L or so. Hydroclay seems to be a very popular choice as are many of the different types of hydroponic gravels but in my first set up I used ordinary 20mm gravel purchased from a landscaping supplier. Anything smaller than 20mm (3/4 inch) will have a tendency to clog over time and reduce the efficiency of your system. One thing I noticed about the gravel when compared to the hydroclay was the tendency for the pH in the system to be more alkaline and I can only attribute this to the gravel having a higher pH than the hydroclay, which tends to be quite neutral. If you can afford it consider using hydroclay. Unlike hydroponics an aquaponics growbed should never need to be cleaned out or flushed and over years of use there will be an excellent buildup of fish poo and other goodies, your growbed will become more productive with age.

Growbed Plumbing

The water from the fish tank must be pumped through the growbed to allow the bacteria and vegetables to do their job of removing the ammonia from the water. Although there are a number of ways this can be performed this website will focus on two variations of flood and drain, traditional flood and drain where the pump is on a timer and floods the growbed at set intervals and flood and drain using an autosyphon, where the pump runs continuously and the water is syphoned out when it reaches a certain level, continuously filling and draining. I would consider these two varients of flood and drain to be the pick of all available aquaponic methods as they are the most efficient and maintainance free. Flood and drain techniques may also be referred to as ebb and flow and if you ever encounter this term rest assured that the two refer to the same thing.

Regardless of which method you decide to use your growbed will require an inlet and an outlet and it is preferable that you make any holes and install fittings for them before you fill your grow bed with medium. When using an autosyphon you only need to create one hole in the bottom of the growbed for the autosyphon, preferably at the opposite end to the pipe that delivers the water from the fish tank into the growbed. Most autosyphon systems have a pipe going from the pump in the fish tank that delivers the water into the top of the growbed. When using the traditional flood and drain technique you will need an inlet in the bottom of the growbed and an outlet at the high water mark so that when the water reaches this level it will drain back into the fish tank. When the flood cycle is complete the pump will turn off and the water will flow back into the tank through the pump so it is important not to have a pump with a one way valve as this will prevent the water from returning. Your high water mark in both types of systems should be about 5cm (2 inches) below the top of the medium in the growbed.

Vegetables

Last but by no means least is the vegetables themselves, half of the reason we chose to DIY aquaponics in the first place. The other half of course is the fish.

The number of different vegetables you can produce in your aquaponics system is staggering, most plants in general will grow well in a well maintained system. Leaf and fruit crops provide the best results however I get mixed reports about the success of root crops, particularly in heavy mediums like gravel where the root cannot displace the medium when it grows and is forced to grow around the gravel, the makings for one very chewy carrot. Overfertilized root crops, particularly potatoes often have bad patches inside them that look like rot and are equally unappetizing. Having said this I have not attempted a root crop myself and suggest to anybody who wants to give it a try to experiment away, no harm in trying. Start with a light growing medium like hydroclay.

As previously stated leaf and fruit crops do grow particularly well. Tomatoes, lettuce, capsicum, cucumber, spinach, silverbeet, rhubarb, celery, zuchinni, cabbage, cauliflower, brussels sprouts, egg plant, broccoli, spring onions, leeks, bok choi, pak choi, corn, pumpkin, beans and more are tried and tested in aquaponics with great success. Fruit grows well in aquaponics and I have heard of systems dotted accross the country that are producing enviable supplies of melons, delicious strawberries and even oranges, paw paw and mandarines. The choices seem hardly less than a normal soil garden.

Planting out your chosen vegetables is really easy. The hydroponic medium does not lend itself to starting off seedlings so whatever vegetables you intend to grow should be started in punnets using soil or vermiculite first and transplanted into the growbed when they have reached a suitable size. You can even purchase your seedlings in punnets from your local nursery and skip the seedling side of things altogether. Now this may sound troublesome at first glance but it actually permits the growbed to be more productive as slow starting seedlings will not take up space in the system until they are well established and ready to grow rapidly. Succession cropping is also easier when the next generation of seedlings is raised outside of the growbed. When the seedlings are of suitable size and you have space in your growbed wash the root systems thoroughly in water and plant them in the growbed so that the root are buried up to the same level as they were in the punnet. There will be a degree of transplant shock but it will be minimal due to the nature of aquaponics.