Stoep Harvest part 10: Rotating your plants

Today on Stoep Harvest we look at the concept of crop rotation. What is it, why do it and how does one go about doing it?

Having spoken to a number of hobby-gardeners over the past few years, there seems to be a general sense of mystery and fear or scepticism around rotating one’s plants in the vegetable garden. I hope to bring clarity and confidence through making this practice easy to understand and apply.

Reasons for rotation

To start off with, there are two core reasons for rotating crops. Both are common sense.

The first reason is to prevent pests from building up. By changing the plant, pest populations that are dependent on certain plants will be unable to increase any further. For example, the carrot fly will want to permanently move to your garden if carrots are repeatedly planted in the same place. By moving your carrots around, the flies will multiply much slower.

The second reason is to prevent nutrient imbalances and deficiencies in the soil. For example, tomatoes consume a lot of nutrients from the soil. Repeatedly planting tomatoes will leave the soil lacking critical nutrients. Each year, the tomato yield will get smaller because of the nutrient deficiency.

In a small urban garden, nutrient deficiencies can be made up by adding fertilizer and compost to the garden. In theory, this would allow repeat planting of the same plant. However, this would not solve the pest build up as mentioned above. In a larger garden or farm, crop rotation becomes critical as the cost of adding large amounts of fertilizer becomes prohibitive.

Doing it properly

The next question is what is the correct sequence of rotating the plants? As with my comments on other topics of organic veggie gardening, there is no set formula here. There is rather a principle of crop rotation that can guide you with the appropriate rotating.

The way I remember this is to divide vegetables into three categories:

1. roots - vegetables such as carrots, beetroot, and radish. Roots need relatively few nutrients to grow.
2. Shoots – plants that we eat the leaves of. This includes lettuce, rocket, and spinach. Shoots are in the middle in terms of nutrient requirements.
3. Plants that create fruits are the most nutrient hungry. This group includes tomatoes, butternut, squash and also the cabbage family.

Once you are clear on the three groups of vegetables (roots, shoots and fruits), choosing what to rotate is simple. My rule of thumb is to see roots as the starting point. After planting roots, follow with either shoots or fruits. Then, after harvesting your shoots and fruits, return back to roots.

As roots use the least nutrients, planting them makes sure that the soil has time to rest and recuperate nutrients ready for the shoots or fruits to be planted. Here are some examples to help make sense further:

• carrot (root) – lettuce (shoot) – radish (root) – tomato (fruit)
• beetroot (root) – butternut (fruit) – turnip (root) – spinach (shoot)
• onion (root) – aubergine (fruit) – parsnip (root) – cauliflower (fruit)

In a small garden, rotating your plants will be more difficult than in a garden with more space. It will definitely test your planning and arranging skills! With pots and box gardens, rather than rotating plants, it is better to replace the soil every few years.

June Planting Table (from seed):

• Western and Southern Cape: broad bean, cabbage, carrot, lettuce, pea, radish, tomato, turnip.
• Inland: cabbage, carrot, pea.
• Coastal KZN: bean (bush and pole), beetroot, cabbage, carrot, cucumber, eggplant, lettuce, melon, parsley, pea, pepper, potato, radish, squash, swiss chard, tomato, turnip.

Next time we’ll be covering the hot topic of companion planting.

By Sam Adams

Sam runs Living Green, an organic food gardening company in Cape Town.