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Crop rotation: breaking the cycle of disease and pests organically in your vegetable garden

Looking for a safe organic way to keep pests and disease under control in your vegetable patch? One of the simplest ways is planting your vegetables based around crop rotation. Crop rotation is all about planting groups of similar vegetables together in a different part of the garden each year. It's important to do this because different crops like different soil conditions. Sweet corn and pumpkin love a rich organical soil, but the same soil conditions would fork carrots and other root crops. Pests and diseases tend to effect vegetable groups and will often remain in the soil for years. But by following a rotation system these pests and diseases can't build up in the soil.

The length of a rotation system can vary from 3 to 8 years. The longer the better. But this can be difficult with the size restrictions of the average backyard. So using a number of resources I've collated a few options for you using a 4, 5 or 6 year rotation system.

4 year rotation

Crop rotation is all about moving vegetable groups from one bed to another each year. Our backyard vegetable patch uses this 4 year rotation system.

The first bed starts off with a mixture of roots crops (carrots, parsnips and beetroot) and vegetables belonging to the allium family (onions, garlic and leeks). The second bed begins with sweet corn and curcurbits (pumpkins, squash, cucumber, zucchini and maybe even some watermelons). By autumn the crops in this bed have usually been harvested so you can grow a quick cover of green manure before the next growing season. The third bed in spring starts with the vegetables that prefer a slightly lower pH (also known as acid lovers) such as tomatoes, capsicums (bell peppers), chillies and eggplants. And the fourth bed can be used to grow legumes (peas and beans) and brassicas (cabbages, broccoli, cauliflower and pak choy). By spring the following year the sweet corn and curcurbits replace the root crops and onions. The tomatoes, bell peppers and eggplants replace the sweet corn and curcurbits (after the green manure has been dug into the bed). The legumes and brassicas replace the tomatoes and their friends. And of course next, the root crops and onions replace the legumes and brassicas. This system continues so that no vegetable group is ever planted in the same place twice over the four year period. Regardless of whether you're using a 4, 5 or 6 year rotation system you can plant leafy salad vegetables like lettuce anytime and anywhere there's a bit of space.

The timing for when you rotate each bed varies depending on the bed and your local conditions. In cool and temperate climates tomatoes and other crops are usually killed off by frosts. But here in subtropical Queensland we rarely ever get frosts (except in the Downs and some parts of western Brisbane out Ipswich way) so we can have a longer growing season. But you'll generally find that all of the beds are usually rotated around autumn in one form or another.

5 year rotation

By now I hope you have a better understanding about how crop rotation works. So I'm not repeating myself I'll simplify the whole 5 year rotation system:

Over time the soil in your beds will gradually become more acidic which suits the way each vegetable group is rotated. By the time you rotate the tomatoes, eggplants and capsicums into the bed in their fifth year the soil will ideally suit their acidic nature. That doesn't mean you'll have to wait 5 years to get your crops. It just means the soil will suit them even better as the years go by. A few weeks before you get to the end of the season in autumn sprinkle a good handful or two of lime or dolomite into each square metre of your tomato bed. This will sweeten the soil preparing the bed for the lime loving onions, garlic and leeks. The other vegetable families are then rotated behind the onions. The whole process benefits all vegetable types and your soil.

6 year rotation

The 6 year rotation cycle splits the legumes from the brassicas so you plant:

The same principles for the 5 year rotation system apply to the 6 year rotation system. As with the 4 and 5 year systems you can plant lettuce, parsley, spinach and silverbeet wherever you have a little bit of spare space after harvesting.

When you're making your beds you can apply a heavy organic mixture of homemade and mushroom compost, old manure, blood and bone and dolomite to beds 2, 3, 5 and 6. Bed 1 should only get dolomite and compost. This way your root crops won't fork from heavily manured soil and your bulbs (like garlic, onions and leeks) won't go mouldy or form poorly.

But what about potatoes?

OK, crop rotation sounds like a good idea, but what about if I want to plant potatoes? This is where you need to start really planning things.

I love potatoes. They're technically from the same family as tomatoes. But I would never have enough room in my tomato bed to fit potatoes in there too. There are only two ways I've found you can get around this (OK three, but the third one is exxeptionally tricky).

1. Make more space. I physically find somewhere else in the garden to grow my potatoes. But don't forget, the same rules apply. You can't plant potatoes (or tomatoes) there for at least four years, unless you want to risk getting disease in your soil.

2. Grow up! Well, make your potatoes grow up. Try planting them in old car tyres like I did back at Norman Park once. Just make sure you don't make the same mistake I made: poor drainage. Drill some holes into the tyre walls to let the water escape, otherwise the soil in the tyres will go sour and you'll get a bad crop. Some gardeners believe the materials in rubber tyres can leach out into the soil (and the potatoes). If you've got any health concerns about this issue, you should avoid doing it. If you've seen any research into this issue please let us know, as we'd also like to find out more.

3. Bring the two together. I've never done this, but I've heard of some over enthusiastic gardeners who graft tomato plants onto the base of a potato plant. Result: potatoes under the ground with tomatoes growing on the same plant above ground. I don't know if this is just an urban myth. But from recent emails from visitors to this site and this link (scroll to the last post on the page), the grafted potato and tomato theory sounds like a dud - but if you've had success let us know.

Whatever rotation system you use it'll be a lot better for your soil and vegies than not rotating at all. If you don't rotate your crops particular nutrients required by individual groups will become exhausted. Rotation helps your soil rest and organically breaks the breeding and growing cycles of pests and diseases. It's the natural method of pest control and soil management.

Last updated 23 October, 2008

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