"Rotate your vegetables so that they do not occupy the same ground until at least 3-4 years latter in order to prevent the buildup of diseases and depletion of certain nutrients as well as to break the pest cycle."
Okay, you might be thinking that I am forgetting the other golden rule:
"Take care of the soil and the plant will take care of itself"
But I'm going to call that the cardinal rule so let's get back to:
Rotation - the basics
Rotation is considered one of the organic gardener's biggest allies in keeping healthy plants healthy but it can make planning the urban veggie patch a little bit trickier. When you add companion planting, microclimates for certain vegetables, interplanting, catch cropping and the like, then you might want to give it up before you even get started so let's break it down.
What are the main rotation groups?
This question is not as easy to answer as you imagine. There are (at least) three ways of looking at it but the most common answer is that crop families are rotated together or at least not planted on the same ground more than once every 3-4 at a minimum years. This is because they can be affected by the same pests and diseases, as well as requiring similar soil nutrients and levels of feeding. Typically these families will include:
1. Brassicas - cabbage, brocolli, kale, turnip, chinese cabbage and many other asian greens, mustards, cauliflower, kholrabi, brussel sprouts etc...
2. Solanacea: tomatoes, potatoes, eggplants, peppers etc...
3. Cucurbits: cucumbers, pumpkins, melons, squash etc...
4. Legumes: peas, beans etc...
5. Alliums: onions, garlic, leeks etc...
6. Asters: lettuce, chicory, endive, artichoke etc...
7. Goosefoot family: beets, swiss chard, spinach, amaranth etc...
8. Carrot family: carrots, dill, fennel, parsnip, parsley etc...
9. Grasses: corn, many cereals, etc...
I could go on (these people do) but you may have already realized that the 'typical' rotation plan for an urban garden has 4 beds so that some families will be planted together. Commonly the 4 plot rotation includes:
1. Roots: carrots, turnips, beets and parsnips
2. Solanums: tomatoes etc...
3. Brassicas: cabbage etc...
Roots are grouped together because similar root eating pests like them. This brings us to the second way of classifying vegetables for rotation: by pests shared across plant families because of an botanical similarity, ie. an swollen underground part. Sometimes potatoes are planted in the roots section but the fact that they are related to tomatoes is acknowledged and it is suggested that the potatoes be kept away from a spot where tomatoes have been planted as well, meaning that you are down to a 3 year rotation in your 4 bed plot or that you have to add some more plots.
On occasion a gardener will micro-rotate so if you grew a row of early lettuce in your other bed, you would avoid replacing it with another crop in the aster family or another leafy green but go with something like a row of carrots or some peas.
The third reason has to do with maintaining soil fertlity and tilth (a fancy word meaning texture). Some crops are heavy feeders and others are lighter feeders so it is wise not to follow a heavy feeder like corn with another heavy feeder as it might grow poorly. Even better, some crops or plants will add fertility to the soil, break up a heavy textured soil or add organic matter, improving the soil. Some people suggest you follow deeply rooted crops with those of shallow roots assuming that they will mine nutrients at different levels.I'll give a rough list:
1. Heavy feeders: grasses like corn, vining crops like squash, many brassicas, tomatoes, peppers and other solanums, celery, spinach
2. Light feeders: roots like beets, carrots, parsnips, turnips, sweet potatoes, turnips, radishes and regular potatoes, legumes, and bulb crops like garlic, shallots and onions.
3. Legumes: Theoretically these increase available nitrogen in the soil. Examples are peas, beans, and clover.
4. Crops with sturdy root systems will break up soil or mine the soil for deep nutrients like dandelions, alfalfa and peas: you can eat all them too.
5. Covercrops like rye and oats can be tilled under, smothered or left to winter kill to increase organic matter in soil. Much more on cover crops
Unless a crop is a big disease risk, like most brassicas, is doing poorly or is a host plant for a particularly annoying slow moving pest, don't always rip it out of the ground. Instead snip it off at the soil line and either let the plant material decompose in situ or compost to add to the garden later. The root system and other organic matter that you left in the ground will help to improve the quality of your soil.
Jeff cox's 100 Great Gardening Ideas has a chart separated by family and feeding needs.
Why rotate your annual vegetable crops?
If you grow the same crop in the same soil and your crop happens to get a disease like clubfoot in brassicas, blight in tomatoes or some other plague, then if you replant it, the disease will effect the plant again. This sounds great in principal but many diseases, like the ones mentioned require longer than the recommended 3-4 rotation cycle to die out. Think more along the lines of 5-15-20 years. Luckily many of us have never encountered these diseases and those who have will want to grow plants that are resistant, employ other strategies to combat along with using rotation.
Of course, you may have a minor ailment in your crop that you do not even notice which is cut off from its host if you rotate and quickly dies out.
Breaking the cycle of pests:
Another commonly given reason for rotation is to break the disease cycle of pests. This makes sense in an agricultural setting where farmers have large acreages and can widely separate crops or can even take a break from growing one vegetable in preference for another one in order to allow for the eggs / larvae to die out without their favourite snack available. It is also important that any alternative host of the pest is removed as well. Alternative host is often code for weeds so mustard is related to brassicas and if you leave it grow then your pest might just 'rest' there.
The problem is that in an urban postage stamp sized garden those Colorado Potato beetles won't mind a spring stroll of six feet to the new planting of eggplants. It will also only work on pests that overwinter near their food source, and then don't travel far to find it aftewards. It has little influence on migratory pests.
A better strategy for pest control is to increase the diversity of plants in your garden and to add lots of habitat for predatory and parasitic critters that will keep the pest population in check. Also don't worry about a pest you don't have or that isn't common in your area (some years you just get an infestation which isn't repeated the following year). If you have reason to worry then one of the most effective method of pest control is barriers such as floating row covers, mulches and plants acting as barriers. Plants exude all sorts of chemicals attract certain insects and others which repell them, as well as influencing the growth of plants around them. This is the basis of companion planting.
Nutrition depletion / loss of soil tilth.
By far the most convincing reason that I can find for crop rotation is soil depletion and explains why it can work to improve plant growth even when using rotation at a small scale. By rotating where you plant such things as corn (heavy feeder), carrots (light feeder) and peas (giver*), you can avoid exhausting the soil. However, any intensive use of soil will require equally intensive care by adding lots of organic matter in the form of compost, cover cropping, or animal manure, keeping in mind that any animal wastes can cause a damaging buildup of salts after awhile.
The practice of fallowing (fancy word for leaving a field alone for awhile) fields was used to allow for nature help rebuild the soil again as all sorts of plant life along with their critter companions, invaded lived, died and enriched the dirt substrate. This resting also allowed for heavily animal manured and irrigated fields to be leached of excess salts. The period of fallowing varied according to the space available and the fertility of the ground and systems. But I digress, you can mini-fallow by letting the weeds grow (I dare you) or by cover cropping with green manures. This does not have to be done in a large scale but just a bit of ground that is currently not growing anything because an early crop has been removed and a later crop is not planned. When I have bare ground - ack! - I throw some peas or other legume and leave them to grow thickly. Usually this happens late in the year after the mulch has broken down under another planting so the legumes are winter killed by hard frosts.
Rotation and companion planting
Companion planting adds another little complication to this whole rotation thing. Especially if you are avoiding planting certain crops besides other ones out of concern for alleopathic (fancy word for nasty) interactions between plants. The big one that I notice on these lists is that alliums (onions, garlic etc...) don't like legumes (peas, beans etc..). You'll notice that these are both light feeders.
There are also some combinations that are supposed to be beneficial such as planting legumes with heavy feeders such as pumpkin and planting carrots which don't appreciate the boiling sun with tomatoes whose foliage gives light shade. The combinations are endless but if you have only a small space then intesive polycropping might be your ticket. There also might be something to this mixed up planting which has its own effect on pest and disease control but I'll get to that in a minute.
Rotation and microclimates
Yup, I'm talking the north-south axis that says that you should plant your tall crops on the northern part of your garden and your short crops in front of them so that everyone gets their fair share of sun. Then there's those little variations in everyone's garden such as the corner with dappled shade part of the day and the hot section near the rock garden. It would make sense to plant the lettuce and brassicas in the slightly shady area and the sweet potatoes in the warm area but what about next year?
You can break up your planting beds so that you have at least three or four tall crop beds and another that has three or four short crop beds but you know that there are only so many arrangements that you can make and at least some of the time, the crops will just be beside the bed they previously occupied. Hardly much of a trick to a hungry pest or annoying fungus.
Some years, you could intentionally plant vegetables where they wouldn't be their most happy and just look forward to those better years but there must be another way.
Rotation - beyond basics, perennials and more
Perennials vegetables and more
If you ever read a veggie patch gardening plan, it will have a spot near the back for perennial vegetables - and by this they almost universally mean globe artichoke for those lucky enough to be in a mild climate or asparagus for the rest of us. (Don't get me started on the multiplicity of other perennial vegetables or at least not today.) In this guideline, it will state that 'As perennial vegetables occupy the ground for many years, they should be situated where they will not be disturbed by annual tilling...' and so on. Hey wait a minute, why do those vegetables get to occupy the same ground?
Let's think about this for a minute. Do you rotate your ornamental perennials? How about that self sown patch of comos? Don't tell me you let it grow in the same ground year after year. Wait, the best blooms wander around the garden you say? So the cosmos does its own version of rotation though not in such an orderly or well separated fashion?
Perhaps you are thinking it's true that we don't rotate our perennials but that they are different than annual vegetables. This is true and not true. Many common perennials are not only related to various edibles but can harbour the same pests and diseases. Golden alyssum is a brassica and there are various attractive asters related to lettuce, oyster root and so on, that we grow as ornamentals. Why don't we rotate them? Well if you have a poorly performing plant because of a disease or pest, I'm pretty sure that any nursery owner worth their salt would suggest planting a new specimen in a different spot. Not only that but it is common wisdom that a related fruit tree should not be planted in the same place that one had recently been grown. So we do rotate perennial plantings just at a different time scale and for more obvious reasons.
I'm fairly confident that we don't run into more problems in the perennial patch because the plants are stronger than your average annual which at the first hint of trouble will rush to seed and keel over, and they are normally surrounded by plants that are not in the same plant family, that have different root systems and have different levels of nutrient needs. The typical perennial flower border is a mish mash of difference rather than an all you can eat buffet of the same plant or plant type in an orderly block.
My whole garden is a veggie patch
Instead of thinking of your garden as made up of specific categories such as a perennial flower bed, potted plants, mixed shrubbery, and vegetable patch, start mixing them up. With especially problematic vegetables such as cabbage, I like to interplant them in a different corner of my yard each year. Sometimes they will be growing along our front walkway, sometimes by the pond and sometimes in the vegetable garden proper. Likewise, planting herbs and other perennials either into your vegetable garden or around the edges, will increase the immediate biodiversity perhaps disuading pests and attracting useful bugs like pollinators. Don't forget that large containers can be used to increase growing space.
Interplanting in all forms can be help including interplanting different vegetable kinds together. One year (okay last year), I had a nice row of purple and savoy cabbage but there were a couple extra seedlings that I had no space for so I tucked them into the flower beds. My lovely monocrop rows grew into beautiful full heads and then bam they were hit with head rot. It travelled along the row decimating my savoys but was slowed by the ever reliable Red Rock Mammoth cabbage. I destroyed all the diseased plant material and was lucky to have a descent harvest despite the disease but in other parts of my yard the savoy were totally unaffected. It was the crowding of all those cabbages right next to each other that allowed for the disease to be worse. So if you want to be really radical there might be something to mixing up your plantings. You can either grow two or three different vegetables together such as carrots and onions that are supposed to repell each other's nemesis pest, or you can go totally wild and plant a pepper beside a pumpkin next to a bean tepee surrounded by lettuce beside ... well you get the point.
Don't stop at with just a vegetable medley but make sure you add some flowers that will attract beneficials as well. Think of what a pretty jungle that would make. Of course, it may complicate feeding and growing regimes such as hilling potatoes but I'd love to see it!
Now that your head is rotating (or is that just me), what should you rotate? It depends on where you are and what you plant. If you have a particular pest or disease in your area then find out the best strategy for dealing with it which may well be rotation. Certainly, I would rotate heavy and light feeders with resting and green manuring to mantain the health of the soil. When it comes to rotation as a preventative measure then brassicas, solanums and root crops are at the top of my list but after that it depends on what you have the room for.
So Ottawa Gardener do you rotate your veggies?
Yes, of course I do. I'm too scared not to. Every single book I have ever read about organic gardening has told me I have to. I think I would start hyperventilating if I didn't but thankfully I grow lots of perennial vegetables which I expect will be living in there spots for some time. I also add as much biodiversity as possible into every square inch of garden space to help nature sort herself out AND if a crop is just too plagued by problems, "I don't grow it." Face it, most urban plots can't support a full year's food supply for a family of 4 so if I can't grow it, I can't grow it or maybe I'll find an alternative. There are lots of tasty green things in this world to share with the bugs.
(This gardening 201 post was made because someone asked me a question - blaim them ;)