Thursday, March 14, 2013

The importance of rotating crops

Are your beetroot plants all leaf and no beet, your carrots forked and the leaves of your potato plants don't look very healthy?  Might not be the vegetables' fault.  It might be because you are not planting your crops in a way that helps them to be most successful.



Many food-gardeners struggle with the concept of crop rotation.  It is something professional farmers do if they are wise, but are home gardens too small to rotate crops?

The answer is rotating vegetable crops is important in all situations if you want good results every year.  In this blog post, after talking about the 'why and how', we have a look at a simple crop rotation plan that can be applied to any food-garden.

Here are the reasons why rotating crops is important:
  1. You do not allow soil-borne pests and viruses associated with a crop to get established.
  2. You avoid depleting your soil of nutrients a particular crop uses.
  3. You can plant crops in a certain succession, so they derive maximum benefit from each other.
  4. You can more deliberately apply compost and organic fertilizers to certain crops and withhold them from others.

Crop rotation applies to:
  1. Established beds intended for a succession of vegetables over a number of years
  2. Annual vegetables, not berries or fruit trees or other more permanent crops
Okay, so in this bed, let's see, here is my garden-diary, I had capsicums two years ago, tomatoes last year, and now, this year, I rotated to having potatoes. That's alright, isn't it?

And over here I had cauliflowers, then radish and now I am trying to grow some swedes, but they are not doing so well.

Crop rotation means not having the same plant variety in the same spot for more than a year.  
It also means not having other members of the same plant family in that same spot either. 

If, over a thee year period, you have capsicums, then tomatoes, then potatoes in a garden bed, you have three members of the same plant family in that bed: not a good idea! Even though they look quite different, capsicums, tomatoes and potatoes are members of the same plant family. Pests and diseases affecting one variety get a real opportunity to establish themselves because they are likely to feel equally at home with all members of the plant family.

Here is a list of the most common annual food-garden plants and what family they are part of.  It is worth realising which vegetables belong to the same family:

Family name

Part of this family are
Amaryllidaceae

Garlic, Leek, Onion (Alliums)
Apiaceae

Carrot, Celery, Celeriac, Parsnip
Asteraceae

Endive, Lettuce
Brassicaceae
(Brassicas)
Asian cabbages, Broccoli, Brussels Sprouts, Cabbage, Cauliflower, Kale, Kohlrabi, Radish, Rocket, Swede, Turnip

Chenopodiaceae

Beetroot, English Spinach, Silverbeet
Cucurbitaceae
(Cucurbits)

Cucumber, Pumpkin, Squash, Zucchini
Leguminosae
(Legumes)

Broadbean, Bean, Pea
Poaceae

Sweetcorn
Solanaceae
(Solanums)

Capsicum, Chilli, Eggplant, Potato, Tomato

One of these plant families plays a special role in crop rotation.  Legumes have bacteria in their root nodules that take nitrogen out of the air and make it available to the host plants and subsequent crops if, when removing the old plants, you cut the stems at ground level or dig them in, rather than pulling the roots out.

Legumes, if planted just before other crops that love nitrogen, can majorly contribute to the success of that next crop. On the other hand, if the next crop does not like nitrogen, it may lead to bad results.  Tomatoes may have many leaves and few tomatoes.  Beetroot may also have great looking foliage, but very small beets.  Carrots may be forked.

The application of compost, manures and fertilizers can very nicely fit in with a crop rotation plan.  You can make sure that you do not apply them for crops that can not cope with too many nutrients.

In books and on web sites you will find crop rotation plans for 3, 4, 6, up to 7-year periods.  These plans involve creating as many beds as there are years in the plan, and each year rotating crops from bed to bed.  Here is a 4-year crop rotation plan that takes most of the factors mentioned above into account.  I reckon it is realistic and workable: 


Year 1
Bed 1


In Autumn apply ample lime, dolomite and perhaps kelp, but not organic fertilizers that contain nitrogen

Autumn – sow Broadbeans and Peas

Spring – sow Beans in late Spring


Year 1
Bed 2


In Autumn apply compost and the full range of organic fertilizers

Autumn – plant/sow Brassicas and leafy greens you want to grow over winter

Spring - plant/sow Brassicas, leafy greens, pumpkins and Cucurbits you want to grow over summer


Year 1
Bed 3


In Autumn add nothing to the soil, but dig, aerate or do other things to make the soil looser and deeper.

Autumn – sow Onions, Parsnips, Beetroot and other root crops you plan to grow over winter

Spring – sow Onions, Parsnips, Beetroot and other root crops you plan to grow over summer


Year 1
Bed 4


In Autumn add compost, dig and aerate the soil or do other things to make the soil looser and deeper

Late Winter – plant Potatoes when the chance of frost is over

Late Spring – Tomatoes and other Solanums eg. Capsicum, Chilli



This is how you set a crop rotation plan in motion:
  1. Autumn is a good time to start your crop rotation plan as most summer crops come to an end.
  2. Divide your vegetable garden into four parts.  These four beds don't have to be rectangular or adjacent to each other.  Any four areas of roundabout equal size are fine.
  3. Using the plan above (or a different plan created by you based on the same principles) decide on your particular crops within the plant families ('we don't like Parsnip, but eat a lot of Carrot').  Many of us will also have to choose between varieties because we can't fit it all in the space we have).
  4. For the first year simply put the crops in your 4 beds as indicated above. The results may not be fantastic because this in only Year 1 of your plan.
  5. Next Autumn rotate your beds: put what is mentioned above under Bed 2 in Bed 1, Bed 3 in Bed 2, Bed 3 in Bed 3, Bed 1 in Bed 4 and from there on rotate every Autumn.

This is not a short-term project.  You will begin to notice benefits after a year or so when carrots no longer fork for example, but only in the fifth year, when every bed has been through the cycle once, will the full benefits become evident.
Whatever crop rotation plan you use, it will be better for your soil and vegetables than not rotating your crops.

If your vegie patch is really too small to divide in four, you can still rotate your crops and gain all the benefits, by making your whole area Year 1, then the following year Year 2 and so on.

Crop rotation, in conjunction with the use of lime, compost and organic fertilisers, as indicated above, should result in continued successful use of a vegetable garden for many decades without having to replace the soil.

I hope you found this blog post useful.  It was a bit tricky to write.  Thank you, Gaye, for your help as proofreader. 

I would very much welcome your comments and questions because they could lead to improvements of this text. Please email foodgardengroup@gmail.com or use the Post a Comment option at the bottom of this post. 





1 comment:

  1. Thanks for a well written article. I've tried to write about it before and it's always a bit tricky.
    When it comes to actually implementing it I find there are a couple of main issues. The first is that you don't always have the same amount of each group of vegetables, so the beds are often uneven in size, or in some seasons there might not even be a certain group to follow on from (unless you leave a whole bed empty for a season, which seems like a waste of space). The other difficulty I've had is that for the last two years I've been adding beds to my garden which mucks up the simple rotation of going from one bed to the next. So I agree with your point that whatever system you use, it's better than not doing it!

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