A Container Vegetable Garden makes good use of available space

Before getting stuck into making a container vegetable garden lets first run through some basics about containers. The shape of a pot can have a significant effect on the performance of plants it holds. Too deep and it could develop a waterlogged area at the base, leading to root death. Too shallow and it could dry out too quickly. Since rapid drying is the more difficult situation to manage, you should opt for moderately deep containers, but make sure there are plenty of drain holes.

A similar contrast exists between plastic and terracotta or 'crock' pots - plastic will not dry out as quickly.

In fact, this is the main point of difference between plastic and terracotta pots. Plastic pots drain better because they have more holes at the bottom, but don't dry out as quickly because water cannot evaporate through the sides. The reverse is true for terracotta. Having said this of course, it does not mean that one is good and the other bad. There are places for both in every container vegetable garden.

Also, many people use trays or saucers under their pots to hold the drainage water. They believe this will save on water, but really it usually only serves to keep the roots continuously wet. Saucers can help prevent a lot of mess, but make them shallow. The alternative is a deep saucer filled with gravel. This will keep the pot itself out of the water and prevent a lot of problems later.

These characteristics of drainage and dryness make things even more difficult when using hanging baskets. The best option is to experiment with different types in different positions until you get the mix right for your own situation.

Adding a vertical dimension to the container vegetable garden is always a good idea for making the most of available space for a container vegetable garden. So, in spite of their inherent difficulties, this makes hanging baskets a very useful inclusion. There are also a few creative ways to use them that we will get to a bit later.

Window boxes and planter boxes tend to be like shallow pots, but can be poorly drained. Again, experiment and add more drain holes if you need them. Click here for more ideas on vertical container vegetable gardens.

A special type of container is called a "Strawberry Pot". These are mostly terracotta (although you may find plastic versions if you look hard enough) and they tend to have all the problems above in combination. Like all unglazed terracotta pots, they dry out through the sides, but at the same time, they have only one drain hole at the bottom, so the soil at the bottom can be easily waterlogged (especially if you use a saucer). Added to this, they can be hard to water properly, so you will need to choose the potting mix carefully (more on this in a moment) and keep a closer eye on them - compared with other pots - adding less water each time, but watering more often.

Having said this, strawberry pots (even the hanging versions) are great for growing strawberries (as well as some other plants) and so will probably be found in almost every container vegetable garden. Just be aware of their limitations and be prepared to experiment with locations and be persistent. Also, don't be afraid to move them around. Strawberries need lots of sun, but on hot days (especially dry, windy ones) move them to a cooler shadier spot.

Potting mixes

The next issue in developing a successful container vegetable garden is the potting mix you fill them with. Again, the problem is getting the right balance between drainage and moisture retention, but 'wettability' is also an important consideration. Some potting mixes (especially those containing Peat Moss) can retain moisture well, but when dry will actually repel water, making them hard to re-wet.

If you do have this problem, there is a simple solution. Find a plastic container that will comfortably hold the entire pot and fill it with water to within an inch or so of the rim of the pot. Now just leave it to soak.

In fact, this is a useful method to remember. It can also be used in emergencies as a rescue attempt for wilting plants and also for leaching out salts (more on this in a moment).

The best potting mixes are based on properly composted pine bark. These mixes need little or no added sand, which makes them relatively light. The composting process also gives the bark a good combination of drainage and water retention properties with little or no re-wetting problems.

There are different grades for different plant types, so don't get stuck with just one. If you are worried about water-logging at the bottom of a deep pot, Try a couple of inches of a very coarse mix (eg. "Orchid mix") at the bottom and your normal growing mix on top.

Whatever you do DON'T use garden soil in your container vegetable garden, it almost never works no matter how good it seems in the garden. The bottom line is that a pot is a special environment with very particular requirements that garden soil simply cannot meet.

Watering pots

I know this sounds simple, but there is an art to getting it right. Also, it is becoming ever more important to make the most effective use of water that you can, so effective watering is one of the most important activities in a container vegetable garden.

Choosing a potting mix that contains a good quality 'hydrogel' can be a big help (especially for hanging baskets), but there are a few tricks you can use anyway.

The first and most important thing to learn is how to tell when pots need water. There are all sorts of high-tech gadgets you can get, but by far the most accurate and reliable is "the human finger"! That's right, I want you to stick your finger into the potting mix (at least 2 inches down). If it feels moist - don't water. If it feels dry - grab the watering can. That's all there is to it.

Now that you know your pot needs water - even though you are trying to be a "Water-wise" gardener, don't be too miserly about it. One of the most common mistakes in container growing is to only just wet the roots. This can lead to a build up of salt that eventually kills the plant.

The most important rule is "Always water until you see water starting to flow out from the drainage holes at the bottom of the pot". this may seem wasteful, but it is important for the long-term health of your plants. Anyway, with a bit of ingenuity, you should be able to collect and re-use the drainage water in the garden to prevent this waste.

Of course, even with the best care, you will eventually start to see a white crusting of salt form on the surface of the potting mix and around the edge of the pots in your container vegetable garden. When this happens, immediately leach the pot in a large volume of water (as described earlier).

After a while, even leaching won't help and growth will slow or the plants may even start to look sick. Don't worry, this probably just means its time to re-pot into fresh mix. Don't forget, an organic potting mix will continue to decompose and its ability to support the plant will eventually decline. when this happens, no amount of water or fertilizer will help - its just time to re-pot.

Using Fertilizer

In many ways, this stuff is over-rated. Its important and its useful, but it is certainly not the universal 'cure-all' that many people make it out to be.

In general I follow the "More and Less" rule: The MORE a fertilizer claims it can do, the LESS I use it. However, containers are a bit different. A good quality potting mix will usually contain a small amount of general purpose, slow release fertilizer - enough for about 3 or 4 weeks growth at least. So there should be no need to add fertilizer when you pot a plant into fresh potting mix.

After a few weeks a teaspoonful of slow release fertilizer like Osmocote® (or a tablespoonful in a large tub) should then keep things going well for another 4 to 6 weeks. If your have repeated this application cycle 3 or 4 times, it may well be time to re-pot rather than add more fertilizer.

If you follow these guidelines and still feel the plants in your container vegetable garden need more, then there is one more thing to try before reaching for the bag of fertilizer.

A good quality kelp extract like Seasol® or Maxicrop® will contain high levels of natural plant hormones. Mix up about 2ml per litre in a watering can (not too much or you could actually stunt the plant's growth) and thoroughly drench everything - leaves and potting mix. This will stimulate the plant to make use of any remaining fertilizer before you add any more.

To make the most of your kelp, try putting the pots into the container used for leaching and emergency watering so you can collect and re-use any spillage or drainage from the 'kelpage' (Sorry, I've been listening to the kids too much).

This is just one of many "Tricks of the Trade" that are always good to know. To keep learning more of these helpful tips for organic gardening, why not subscribe to our Free email newsletter - The Food Gardener.

Further Reading and useful links

Choosing vegetables for your container vegetable garden.
Some vegetables a better suited to a container vegetable garden than others. This page has links to information on a wide range of vegetables that can help you make the best choices.

Companion planting
Containers offer opportunities for companion planting,as well as for growing companion plants for use in other parts of the garden.

Growing herbs
Many herbs are best grown in containers, as they can interfere with the rotation of plants in the vegetable garden.