For Hawaiian gardeners, the concept of crop rotation can be confusing if you are relying on information designed for temperate and subtropical growing environments. ADVERTISING For Hawaiian gardeners, the concept of crop rotation can be confusing if you are relying
For Hawaiian gardeners, the concept of crop rotation can be confusing if you are relying on information designed for temperate and subtropical growing environments.
Three- and four-year rotation is out of the question when you typically can grow that many crops in a single calendar year.
Crop rotation appears to be complicated, but taken at its simplest, crop rotation is just that, the rotation of mainly annual crops grown in a particular location. The more different types of plants, or more specifically plant families, you can grow, the better the rotational value you will get.
But why should you practice crop rotation when all you want are lettuce and tomatoes?
First, by growing the same thing again and again in the same location the disease and insect pests that favor that crop can build up to levels where you can’t grow the crop or will require much more pesticide application.
For example, nematode might be present in your garden soil in low population numbers. When you grow a susceptible crop, the population can build up in the soil during the crop’s lifetime. Grow the same crop again and the crop plant does not have the benefit of a low nematode population in which to start out.
This higher population of nematodes can very well overwhelm the crop plant even before growing past the seedling stage. Larger, more mature plants with an extensive root system can tolerate the attack of a higher number of nematodes much better than seedlings.
When rotating with a crop that does not favor the increase of nematodes, you can reduce the population numbers back to a low level
Start by dividing your garden into definable plots you can use for most of your crops. If your bed sizes are small, don’t worry since you can combine smaller plots to make larger ones when the need arises, such as when planting large vining crops including pumpkins and melons.
Crop rotation can be practiced on any scale, even down to the pot or container garden level. Be aware that with smaller plot size and closer proximity it might be harder to keep disease or insects from spreading to the next planting.
Draw a map of your garden plots and label each section. Make a list of all the crops you grow and include all those you would like to grow. This just might be the incentive to get you to plant that never before tried vegetable.
Categorize your entries by botanical families. As a guide, the most common garden families in Hawaii are the following 12 families:
• Fabaceae (beans, peas, peanuts, clovers, sunhemp).
• Chenopodioideae (beets, chards, spinach).
• Brassicaceae (cabbage, kale, broccoli, radish, mustard).
• Asteraceae (lettuce, sunflower, daisies).
• Convolvulaceae (sweet potato, morning glory, ong choy).
• Liliaceae (onion, garlic, chives, leeks).
• Cucurbitaceae (squash, pumpkins, gourds, cucumbers, melons).
• Solanaceae (tomato, pepper, potato, eggplant).
• Apiaceae (dill, celery, cilantro).
• Graminaceae (corn, grasses).
• Araceae (kalo, taro, malanga).
• Malvaceae (okra).
The reason to group by families is that members of the same family are more likely to extract common nutrients from the soil, have similar pest and disease problems and can contribute to the improvement of soil in general.
Members of the bean family are widely regarded in crop rotation because they are noted for fixing atmospheric nitrogen that subsequently can be used to support growth of plants in future plantings, especially leafy crops that require higher levels of nitrogen to grow well.
Various other crops are known to reduce nematode population through various mechanisms, such as sunhemp, certain marigolds and members of the brassica family.
Planting cultivars bred to be pest and disease resistant also helps tremendously. Some of the mechanisms involved are non-host, where the nematodes fail to develop or reproduce; plant production of chemicals that roots release into the soil; and those that release toxic compounds upon decomposition in the soil.
I would suggest a four or five family rotation, where members of the same family are not planted for at least that many crop cycles.
The easiest rotation would involve four garden plots and plants from four families. Each plot gets planted with a different family and the family changes with each planting until all families are planting in a location. In time, plant families can be substituted to provide a wider variety of crops.
To ensure your rotational practice follows a desirable course of action, keeping good planting records is essential. An added benefit of the written planting record is you will have a history of exactly what you planted and when you planted.
With a few extra notes on how the particular cultivar preformed, disease or insect problems, fertilizer application, etc., you have a great garden journal. This also allows you to plan for future planting location for various crops to match production with needs.
What about garden perennials such as asparagus, banana, papaya or even herbs?
Crop rotation can and should be practiced on these crops; however, the cropping duration will be measured in years. Cover cropping and/or companion cropping becomes very important for these long-cycle crops, but more on that is a future article.
The key is knowing what was planted prior and what can go in next.
For more information about this and other gardening topics, visit the CTAHR electronic publication website at www.ctahr.hawaii.edu/Site/Info.aspx or visit any of the local Cooperative Extension Service offices around the Island. I can be reached at russelln@hawaii.edu.
