Good news for all those who don’t have a garden of their own: Gardening in a pot garden is just as much fun! Pots and other plant containers can find a place on even the smallest balcony, terrace or even window sill. However, potted plants are somewhat more dependent on your help than their colleagues in the open. This is because the water and nutrient supply is limited in the small planters and the sensitive root zone is exposed to strong temperature and humidity fluctuations. There is also the question of which type of planter is most suitable and which soil is best to use.
Enough space for the roots in the pot garden
The small, thin-walled plastic pots in which herbs are sold in nurseries, garden centres or by mail order are only a stopgap solution for a short time. The containers are far too small for healthy development.
So free the plants immediately after purchase and repot them in larger containers. The roots need as much space as possible to develop. The bigger the pot, the better for the plants! They grow more yieldingly and are less susceptible to pests and diseases. In addition, large pots can store more water, which pays off especially in sunny locations. Plants that develop a lot of root mass or long tap roots need deep pots. A pot that is too narrow is also problematic because the root zone heats up quickly in the sun and dries out. Such stress situations weaken the plant’s defences. Aphids in particular benefit from “root-weakened” potted plants.
Which planter is the right one for the pot garden?
Planters come in all shapes and sizes and in a wide variety of materials. Each material has advantages and disadvantages:
Plastic pots: Plastic causes many environmental problems. Planters made from it are cheap and, above all, lightweight, which is a weighty advantage for large pots. In addition, plastic pots are frost-resistant and retain moisture relatively well. If watered improperly, however, there is a risk of waterlogging, which can lead to rot in the root zone. There are now plastic pots in a rustic terracotta design that also have very sturdy walls and can certainly compete visually with the original.
They have a better stability than light, thin plastic containers. Clay pots: Clay pots are made of natural material and are breathable, but the water evaporates relatively quickly through the pot walls. You will therefore have to water more frequently with such pots. In addition, the evaporative cooling causes the potting soil to cool down. This interferes with the growth of heat-loving plants such as tomatoes, which do not like cold feet. Large clay pots are very heavy, expensive and unfortunately also fragile and sensitive to frost.
Due to their own weight, however, they have good stability. A speciality are the decorative terracotta pots, which are often a design element in themselves. With clay, a patina of lime efflorescence or moss forms very soon, an effect that is sometimes even desired as an “aesthetic”.
If you want to avoid this, you must use glazed pots or earthenware pots. Efflorescence can be removed with vinegar water and a brush. Wooden pots and baskets: Wooden planters or baskets are sensitive to moisture and weather easily. They must therefore be covered with foil, whereby you should make sure that there are drainage possibilities for the water.
Avoid waterlogging with water drainage hole and drainage
No matter which containers you choose: It is always important to ensure good water drainage. Waterlogging is critical for most plants because the roots start to rot and the risk of fungal diseases also increases. The containers must therefore have one or more water drainage holes. If necessary, you will have to drill holes in the bottom of the pot yourself.
The water drainage holes in the bottom may be protected from blockage with shards of clay from broken flower pots. For larger pots, a drainage layer of gravel or expanded clay makes sense so that excess water can drain off easily. Fill in the potting soil on top of this. Leave a space of about three centimetres to the top of the pot or container so that you can water the plants without the water overflowing.
With perennial plants, you should keep an eye on the growth of your protégés, because even a large pot will eventually become too small. When the roots grow through the drainage hole in the bottom of the pot, it is high time to repot. The best time of year to do this is spring. It would actually be sensible to plant the plants in a new, slightly larger container with fresh soil every year. For large potted plants, however, every two years is sufficient.
Watering the pot garden: finding the right balance
In contrast to garden plants, the roots of potted plants unfortunately only have a limited amount of soil at their disposal. In windy and sunny places, evaporation losses occur and a pot can dry out very quickly. Therefore, you should regularly check the humidity.
Water the pot garden moderately but regularly
In order to have to water less often in summer, people are inclined to water vigorously. But the stark change between extremely dry and extremely wet means stress for plants. That’s why it makes sense to water regularly, but moderately. Depending on the location and the plant, this can be twice a day or only twice a week. The pot size is also crucial, because the more soil, the more water can be stored.
More watering tips
Here are some more tips on how to do your plants some good when watering:
It's best to water with rainwater or with stale tap water. The best time to water is early in the morning or in the evening. Water only the root ball and not the foliage, otherwise the risk of fungal diseases increases. To reduce evaporation losses, you can mulch the potted plants with grass clippings. To reduce the need for watering, there are also special water storage containers or automatic watering systems.
Now all that’s missing is the soil for the pot garden – but which one?
In contrast to a real garden, a pot garden has the advantage that you can easily adapt the potting soil to the needs of your plants. This is because the different vegetables and herbs have different requirements in terms of nutrients and pH value. That is why the trade offers many different substrates. The substrates available for sale are ready-mixed soils that are tailored to the different needs of the respective plants by adding additives. The composition of the substrate depends on the intended use.
The right soil for heavy growers like vegetables and fruit
Potting soils such as vegetable soil, raised bed soil, compost soil or universal soil are well suited for growing vegetables and fruit in pots and tubs. They contain sufficient nutrients for heavy-duty plants. In addition, they usually have a pH value between 6 and 6.5, which most plants do well with. Special substrates for bog plants have a lower pH value of below 5, which blueberries or cranberries, for example, absolutely need. Citrus plants also prefer acid soil.
Special soil for weak growers like herbs
Plants that like it dry get substrates with a low nutrient content and many mineral additives such as sand or lava granules. Special soils for herbs and other weak growers have a lower fertilisation and more mineral components than comparatively the substrates for ornamental plants, i.e. potting soil, or vegetables.
If you plant several different herbs in a large container, make sure that these plants have similar needs in terms of soil, water supply, fertilisation and sunlight. For example, plant chives, chervil, spinach or radishes in one container: they like even moisture and partial shade. Or form a community with thyme, savory and marjoram: they love full sun and lean, well-drained, calcareous soil.
If possible peat-free and without synthetic additives
The main components of the substrates available for sale are organic materials such as peat, green waste compost, bark humus, coconut fibres, wood fibres and rice husks. In addition, there are inorganic additives such as sand, gravel, pumice, clay, expanded clay, brick chippings, perlite, lava granulate, algal lime or primary rock flour. There are also synthetic additives such as polystyrene, hygromull, styromull and Agrosil®, which are best avoided.
Peat, the most common raw material for substrates, should also not be included from an ecological point of view. The peat bogs, which are available in limited quantities and only grow back extremely slowly, are habitats for many endangered plant and animal species. In addition, peatlands are incredibly important CO2 reservoirs. Nevertheless, ten million cubic metres of peat are sold to leisure gardeners in Europe every year. Some suppliers replace peat with other materials such as green compost, bark humus, wood or coconut fibres. These sustainable, peat-free products should be preferred for your pots, tubs and balcony boxes. A shopping guide for peat-free soils is available from BUND.