Introduction

Container gardening is the practice of growing plants (for food or decoration) in pre-prepared containers filled with fertile growing medium instead of directly into the ground. Container gardening is an alternative to in-ground cultivation where the ground is unsuitable for plants. This could be because it is contaminated, inaccessible, or otherwise unusable. This is commonly the case in urban areas, where the ground is often in an unsuitable condition for cultivation.

Container gardening brings with it many benefits. Since the growing medium is chosen, it can be tailored to the needs of a given plant type, thereby increasing yield per area up to, or even beyond what could be achieved in farmland. Container gardens can also thrive almost anywhere, including indoors (for certain plants), and on the roofs of built structures. This means that urban dwellers with otherwise limited access to open space, and no access to fertile land can still grow enough food to provide a healthy supplement to their daily nutrition. For people with sufficient roof or yard space, urban gardening can even be scaled up beyond the subsistence level to form profitable urban farms.

This chapter sets out the steps for starting and maintaining an urban garden, or small urban farm, including advice on how to avoid or solve common problems that affect crops and yields. The focus is on food crops, but many of the ideas carry over well to other crops.

The flexibility in terms of the size and shape of containers allows urban gardens to thrive in a wide variety of situations.

Photo: Mripp (CC-BY-SA 2.0)

Preparation of Containers

The Equipment chapter details various types of containers that can be used. Preparation for planting is as simple as placing a sufficient volume of compost or vermicompost inside without compacting it (never compact potting soil). For some plants, increased porosity and aeration are required. For these, the compost will need to be ‘broken up’ with a rough substance which will introduce air holes and porosity. River sand, and gravel can serve this purpose well. Make sure that whatever material you choose is free of chemical and biological contaminants (eg leaked fluids from vehicles or untreated waste) and plant pathogens. Do not use so much of this bulking material as to risk starving the plants of the nutrients in the compost.

The next important consideration is container placement. In general, less shade is better because any excess sunlight can be controlled with shade netting. If low light or extensive shading is completely unavoidable, and supplementing with artificial light (potentially expensive) is not possible, rather grow shade-tolerant plants.

All of the activities set out below are individually simple and easy to perform for the vast majority of people. However, good record keeping can still help elevate the efficiency of the hobby or subsistence urban farmer. Recording observations helps to build a knowledge base for future seasons, which can be very valuable. At the very least, labelling the containers helps to easily identify the various plants. The records do not need to be complicated and can be written or recorded in whatever medium is most comfortable.

Good record keeping is a must for any urban farmer wishing to sell their produce as a business. A business, of any size, lives and dies on the quality of its processes.

An example of a simple record used to keep track of a garden.

Preparation of Seedlings

As with the full grown plants, different seeds require different conditions to germinate and grow into seedlings. Optimise the conditions for each kind of seed you have to maximise the germination rate. The table below lists some common seeds and ideal germination conditions.

Germination Guide for Common Crops

*warm, dark and moist conditions can be achieved in most cases by sealing the seeds in a wide-mouthed glass bottle with a moist cloth and placing the jar, covered, in warm conditions (for example, well covered on a sunlit window sill). Ensure you regularly (daily) unseal and ventilate the jar--it is sealed to trap moisture, but the seeds require oxygen (fresh air).

**very important, do not let the soil dry up for any length of time, or the germination rate will decrease dramatically. Also do not waterlog soil, which will cause compaction

Notes:

• Plant cool weather plants in late autumn for harvest in spring at the latest, and warm weather plants in early spring for harvest in autumn at the latest

• Most seeds can be germinated in place (direct sow), but for other types it may be too difficult to maintain the right conditions when they are already in the container. For these, it is often more effective to germinate them outside the soil in ideal conditions, and then plant the sprouts.

• The majority of common seed types can be sown directly in the growing container, watering only enough to make the soil moist--not wet or muddy, and not allowing it to dry.

• You can also place a cold frame over the container to help trap warmth and moisture until the seeds sprout, but this is optional. Be sure to remove the frame when the sprouts show.

• For commercially prepared seeds, the manufacturer often includes germination instructions on the packaging. This information includes expected germination rate, ideal planting time, planting depth and other useful information. Use this information to optimise your planting.

• Planting time is determined by the environmental conditions that the plant will be exposed to. Summer plants prefer warm conditions, and winter ones prefer consistently cooler temperatures.

Companions

Companion planting is the process of selecting different species of plant to grow at the same time, physically close to the main plant--in the same container in this case--to achieve benefits for both. Generally, the benefit is improved yield for one or both plants, but it can also be pest control. The most common companion pairs generally include a nitrogen-fixing plant which boosts the growth of its companion. A larger companion can also help smaller ones by breaking up and loosening the soil with their roots, which allows the smaller companion’s root network to grow larger than it could on its own. Larger plants can also act as a natural trellis (physical support) for creeper companions.

Companion planting does not necessarily need to be limited to two species per container. However, be aware, when combining more than two species, of possible interactions between all of them
The table below shows some proven companion pairings for common plants.

Companion Planting Guide for Common Crops

To use the table, first choose your main crop in the vertical column labelled 'Primary'. Then, read along that plant's horizontal row to find a companion to plant in the same container. If a cell is marked as either ‘OK’ or ‘AVOID’ read from the heading of the column what plant the assessment refers to. The entries at the end of the row are supplementary. If you choose to have more than one companion, repeat the process for the second crop to ensure it will not clash with the others.

For example, if your chosen crop is beetroot, reading horizontally along that row shows one cell marked 'AVOID' and two marked 'OK'. The 'AVOID' cell is in the 'Beans' column, meaning that beetroots and beans should ideally not be planted in close proximity. The 'OK' cells are in the 'Peanuts' and 'Onions' columns, meaning beetroots can be planted together with either of those two species. If you want to plant all three together, then you need to re-do the check to make sure there is no conflict between onions and peanuts, by looking up either one of them in the 'Primary' column.

In this case, note that the 'Onions' row has a cell marked 'AVOID' in the 'Peanuts' column, meaning that the three species (beetroot, peanuts and onions) should not be planted all together.

For the cells which are not marked either way, there is not enough information about that pairing to make a conclusion one way or the other.

Monitoring Growth

There is not much that a healthy container garden requires. Weeds are rarely a problem, so regular weeding is generally not necessary. Pests can be an issue, however, so it is important to regularly inspect the plants. Inspect leaves, stems and the soil surface for signs of unwanted invaders. Essentially, anything other than vibrant green leaves (with no holes in them) may indicate a problem. The Challenges and Solutions section of this chapter lists common pests, and ways to deal with them.

The other factor to monitor is water availability. It is very important to ensure that the plant has adequate access to water, and no more. Too much water can be just as big of a problem as too little. The best way to monitor soil moisture is to sample the top layer of the soil. Stick your finger into the soil. It should come out moist, but not covered in mud. If the soil is too hard to stick your finger in, you have a problem. It is either too compacted and needs to be broken up, or it is far too dry. Potentially both.

Water plants in the morning before the day reaches its hottest point. This allows the water time to infiltrate into the soil without quickly evaporating, but also prevents the roots and foliage from remaining wet overnight.

Adding extra fertilizer will generally not be necessary if you used fresh compost or vermicompost as the growing medium. However, it may occasionally be necessary to supplement plant nutrition using ‘worm tea’ or compost solution during the season, depending on the condition of the growing plants.

Besides these general considerations, specific plants may require special attention at particular times. For example, it is important to be vigilant with potatoes to make sure the tuber is never above ground--exposure to sunlight causes potatoes to deposit a protective layer of solanine (a green substance which is mildly poisonous to humans) in their skin. Other plants may require trimming or support. Look up detailed guidelines for your chosen crop(s) online (there are numerous free resources) or seek advice from a more experienced grower. However, the point of these 'extras' is generally to maximise productivity, so failure to perform them will not necessarily doom the harvest to failure.

The most important things to ensure are that the starting soil is healthy, it is kept correctly moist, and the plant itself is inspected routinely. Beyond that, you will probably be able to figure out for yourself what (if any) interventions may be required.

Plant diseases can come from a variety of sources, including physical contact with infected material (cuttings, soil etc). Good quality compost is generally pathogen free because the digestive processes of the worms (vermicompost) or high temperatures during the process (thermophilic composting) destroy such vectors. However, there is still a small chance for your crops to get infected. Regular inspection can catch these problems in the early stages and give you the best chance of fighting back, or at least minimising the spread.

Protection Measures

Your crops also require protection from weather conditions that can cause major damage within a few minutes or hours. The major hazards are excessive heat, cold, hail and wind.

The simplest solution to all of these problems is to simply move the container itself to somewhere less damaging to the plant. However this may not be practical if the container is large and heavy or if there are a large number of containers to be moved. The other solution is to provide protection in place, using either netting or a cold frame.

Shade netting is suitable for all the required protection in the summer months, as well as frost protection in winter. However, it will not keep a plant healthy if the ambient air temperatures are too low. It only prevents the direct damage caused by dew settling on leaves and freezing overnight. When it comes to hail protection, it is important to be proactive. If you have access to weather information that differentiates between hail risk and normal rain, you can selectively place the netting whenever a risk of hail is reported. However, if you do not have access to accurate information, then the only way to be sure is to place the netting over your vulnerable plants every time it is going to rain. Many crops do not need hail protection, while others may be badly affected. Vine and berry crops are sensitive to physical damage.

The same is true in late autumn when temperatures drop and overnight frost becomes a risk. It is necessary to place the netting at sunset before the air cools, so that dew settles on the netting and not the leaves. Frost is unpredictable, but a single episode can wipe out the harvest, so diligence is key in this respect.

A cold frame is suitable for keeping summer plants alive and productive in the cold winter months, by maintaining higher air temperatures inside it than the outside air. It acts like a mini greenhouse for each plant container. Cold frames should not be used for protection during summer months because there is a serious risk of the greenhouse effect overheating and damaging the plant.

Harvesting

Although the maturation times are a good guide, the exact time taken for a plant to reach maturity, or harvest readiness depends on many variables. The species, variety, environmental conditions and individual differences all play a role. For this reason, all instructions with respect to harvest time are necessarily guides. It ultimately comes down to visual inspection to determine when the crop is ready.

Having records for this purpose is very useful as it allows you to get ever better at anticipating and recognizing an approaching harvest by consulting records of the previous season’s observations.

The table below lists some of the visual markers of a mature harvest, as well as the expected time to reach it, for a few common vegetable varieties.

Harvest Guide for Common Crops

When harvesting keep in mind that your vegetables may not look very similar to supermarket varieties. They may be larger or smaller or differently coloured. Don’t allow this to mislead you, but rely on regular inspection and observation (and record keeping) to guide you

Preparing for the Next Season

The soil used in container gardening can theoretically be reused with minor adjustments. However, best practise is generally to replace it with freshly prepared compost. This is not always practical if the domestic supply of compost is insufficient to replace the contents of every container.

Another option is to mix a third of fresh compost with two thirds of reused soil, making sure the mixture is well aerated.

Finally, it is possible to fully reuse the previous soil, while replacing lost nutrients with worm tea or compost tea. This can extend the life of the soil for longer than one season, but is unlikely to be as effective in the long term as replacement.

If the plants that grew in it were infected by a soil-bourne pathogen then the potting soil must never be reused (partially or fully). It is not worth the risk to subsequent crops. In addition, the container itself needs to be thoroughly cleaned and disinfected, or the lining replaced.

Used potting soil can be added to a compost heap (only if it was not infected or infested with parasites), or used as a general soil amendment in the yard. If there is no other option, then as a last resort, used compost can be landfilled without harm to the environment.

Challenges and Solutions

This section will help you prevent or identify and solve a few common problems associated with small scale agriculture

Failure to germinate
The key to everything, naturally is seeds (unless you acquire seedlings to start with), without which there can be no growth. Germination can be so easy that children can do it (bean seeds) or it can be a challenge to achieve consistently. Below are the main reasons that seeds may fail to germinate.

• Time: Some sees begin to show signs within days, others may show no change for weeks at a time. What may appear to be germination failure can sometimes just be a delay.

• Moisture: Most seeds require a moist environment as a signal to germinate. Too little water triggers dormancy, but too much can cause spoilage (rotting). For some seeds with a tough coat, you can make a small cut in the seed skin to allow moisture in, and speed up germination.

• Light: Most seeds germinate in darkness, meaning they must be in the soil or covered up completely. Others are triggered by light, and will remain dormant in darkness regardless of all other conditions. Make sure you know which category your seeds fall into.

• Depth: For seeds that have been directly sown, the planting depth can be the difference between failed and successful germination. Make sure to follow the depth guideline carefully--a seed planted too deeply may not have a long enough shoot to reach out of the soil even when all other conditions were met.

• Viability: Finally, seeds do not remain viable forever. Correct storage can help extend their life, but stored seeds will eventually be incapable of germinating, regardless of the conditions. Plant seeds as soon as convenient, and store unused seeds in the correct ways, as recommended by their supplier. (Most often in darkness, totally dry, sealed, and cool or chilled.)

Wilting
Wilting refers to the loss of turbidity (springiness) of the plant’s soft tissues; mainly leaves, flowers and stems. It is caused by a softening of the walls of individuals cells making up the tissue and can be caused by several different conditions.

• Drought conditions: this is probably the most common reason for wilting. When the plant does not have enough water, it can begin to wilt within hours. If wilting is accompanied by dry soil, and (perhaps) very hot weather, then this is the most likely cause. Water the plant, ensuring that the soil remains moist (not wet, not muddy).

• Low temperature: Consistently cold ambient air can cause wilting in plants that are not cold-tolerant. If wilting occurs despite adequately moist soil (perhaps overnight during a cold spell or with winter approaching), then low temperatures are a likely cause. Place a cold frame over the container to keep the plant warm.

• High salinity: If the mineral content of the water used to water the plant is excessive, or if the soil itself has been exposed to salts, then this could lead to wilting under otherwise ideal conditions (not too cold or hot, and soil correctly moist). This situation is unlikely to occur when using normal drinking water, and correctly prepared compost.

• Soil saturation: Soil saturation refers to a condition in which the soil is ‘holding’ the maximum volume of water that it can, and is essentially ‘flooded’. Under these conditions, all voids (gaps/spaces) in the soil that normally contain air are filled with water, allowing no oxygen to reach the roots, and essentially drowning the plant. Thus, somewhat ironically, both too little and too much water lead to the same visual condition--wilting--but for very different reasons. If wilting occurs in the presence of excessive water or mud, then overwatering is the issue. Cease watering, and add drainage holes to the container to speed up flow of water. After the saturation water has drained away, soil compaction may be a problem. Gently try to break up the soil in the pot (being careful not to damage the roots) to improve aeration

• Disease: Finally, another cause of wilting could be a disease which is affecting the plant’s internal systems. There is not much to be done in this case except isolate the plant from the rest of your crops and monitor it carefully. Consult an agricultural extension officer or experienced farmer if you suspect your crops have been infected. Plant diseases often present with other symptoms that you can use to double check and make sure it is not one of the other reasons.

A wilting plant. Note the loss of rigidity and the change in colour and shape of the leaves.

Stunted growth
The ultimate goal of vegetable cultivation is to maximise the yield of the edible portion of the crops. For some plants (eg beetroot) that is almost the whole plant, and for others (eg tomato) only a fraction of the total mass. Stunted growth could refer to the whole plant or to the edible part only. Stunting can be difficult for an inexperienced farmer to even spot, because they may not be familiar with the standard size to expect from a given species. Record keeping (size, growth rate etc) can help you get better at spotting this problem as the seasons pass. Below are some causes of whole-plant stunted growth. That is, when the entire plant is smaller than it should be.

• Nutrition: Like any other growing organism, if the plant lacks nutrients (eg nitrogen) it will not have the building blocks required to turn into new tissue and will be stunted. This should not be a problem when using fresh, well-made compost as the growing medium because it provides complete nutrition for plant growth. However, when working with partially or fully reused potting soil, the plant’s nutrition may need to be supplemented with worm tea or compost solution. These are both made by simply soaking compost or vermicompost for several hours in clean water to extract the nutrients, then watering the plant as normal using this nutrient solution. This method should adequately solve any stunting caused by undernutrition.

• Nutrition: Like any other growing organism, if the plant lacks nutrients (eg nitrogen) it will not have the building blocks required to turn into new tissue and will be stunted. This will not be a problem when using fresh, well-made compost as potting soil because it is complete nutrition for plant growth. However, when working with partially or fully reused potting soil, the plant’s nutrition may need to be supplemented with worm tea or compost solution. These are both made by simply soaking compost or vermicompost for several hours in clean water to extract the nutrients, then watering the plant as normal using this nutrient solution. This method should adequately solve any stunting caused by undernutrition.

The following may be the cause of undersized yields where the rest of the plant is growing normally. For root crops (eg carrots), this problem will unfortunately only be evident after the plant is harvested.

• Soil compaction: This primarily pertains to root and tuber growth. If the soil is too tightly packed, then the underground portion of the plant will struggle to physically push enough soil aside to allow good growth. Therefore, when planting tubers and root crops, it is absolutely essential to ensure that the soil is very loose and fluffy and does not compact over time.

• Temperature: Many summer vegetables are biologically signalled to stop growing if the temperature drops below a certain threshold, even for a day or less. Therefore, when cold temperatures are expected, take preventative measure and protect them with cold frames. Conversely, some cool season vegetables are signalled to stop growing by hot temperatures. For these plants, shading may help to keep them cool, but the only lasting solution is to correctly time their sowing so that they grow during the cooler months.

• Water: Certain plants (tomatoes, cucumbers)have a high demand for water to produce a good yield. For these crops, it is important to ensure that they are never short of water. This will help to ensure consistently good growth over the season. Be careful not to saturate the soil, however. That will not be helpful.

Pests
Pests can be any agents whose presence or action acts to either damage or kill the crops. This can refer to insects, birds or even small animals. That is not to say that all fauna are bad for the crops. In fact, some (eg earthworms) are actually very good for the plant’s health. Thus, if you spot insects or other agents among the plants, do not assume they are harmful, They could well be boosting the harvest, or protecting the crop by eating actual pests. There are too many different kinds of pests that could conceivably affect your crops to name them individually, so instead, below is a list of signs to look out for that indicate that something is wrong, but not necessarily what pest could be causing it:

• Damage to leaf structure/fruit (lots of holes)

• Discolouration of leaves/fruit/flowers (check undersides also), unusual surface coating

• Visible presence of large number of pests/eggs/larvae

If you suspect an infestation of pests, there are a few measures you can take to try and fight back:

• Garlic/pepper tea/lemon juice/onion juice: these substances are all safe for the farmer and the plants, but can have a strong repellent effect on certain pests when sprayed on leaves, soil or container surfaces

• Mulch: a layer of mulch over the potting soil might help disturb the pests’ lifecycle and slow their reproduction

• Heavy water spray (physical removal): a stream of water can be used to dislodge some kinds of pests from leaves

• Row covers/ fine netting can provide a physical barrier to larger pests

Generally, it is unwise to try to introduce biological control by introducing competing fauna that will predate the pests. The results of this type of intervention are both difficult to accurately predict, and challenging to reverse, and thus best left to experts. If none of your interventions are effective, consult an agricultural extension officer who may be able to guide you in taking stronger steps.