Crop Rotation

Question from Sharon:
I admire you so much and all you do.  I have a garden plot in a community garden in Santa Monica. I know how important it is to rotate crops and I do as much as possible given the small space that I have. I grow veggies year round being blessed to live in Southern California.  Here is my question. If I grow a tomato plant in a particular spot over the summer and then, after amending the soil when the tomato plant is out, plant a cool weather crop like root veggies or greens in it’s place over the fall and winter, will it be safe then to plant tomatoes, peppers, etc. in that same spot the following summer?  Also, are you lecturing at all in 2012? If so, I would love to attend.

Answer from Pat:
First regarding crop rotation and tomatoes: Planting winter crops after summer crops, such as tomatoes, counts as one rotation but one needs three or four rotations to keep soil pests and diseases at bay. Unfortunately, peppers and eggplants are also solanaceous plants and thus in the same family and subject to the same diseases. I truly believe in crop rotation and wish we could all practice it, but it isn’t always possible in a small garden. For example in my own experience when I filled two terraces with vegetables, there were only two good places to plant tomatoes and so that did not provide enough rotations for me to follow the 3 or 4 crop rotation rule, and currently I am growing vegetables in only one raised bed in full sun. This is all I can really care for today. Unless I plant tomatoes in containers, I’m stuck with just one place for growing tomatoes after harvesting my winter crops which are in that raised bed now.

I think if this or a similar situation is the case, one must simply roll with the punches and do one’s best. In my old terrace gardens as the years went by my tomatoes had more problems with late blight and early blight, and this was because I couldn’t practice proper rotation. However, I always grew disease-resistant varieties and despite problems I soldiered through and had a decent harvest. The latest idea now is to plant heirloom varieties that have been grafted onto disease-resistant roots. This could solve a lot of problems. I have some other suggestions too: If despite my best efforts, tomato diseases eventually build up in the soil I might forgo raising summer vegetables there for one summer and use soil solarization on that bed (as described on pages 295-96 of my organic book.) Finally, it is important to keep a clean garden, taking off and destroying brown leaves, for example, and I have often thought that one could take off the top layer of soil where tomatoes have grown and replace with fresh soil from somewhere else in the garden and then also amend with organics, of course, as per usual. Mulch helps too and homemade compost does much to deter the development of soil-born diseases. And now today we have relatively new organic and biological products, such as Serenade™, which is a great addition to our arsenal of weapons for fighting the diseases of plants.

Besides several diseases, most tomato varieties that are not VFNT are prone to nematodes. In my current raised bed if nematodes ever should become a problem I would treat the soil with shrimp shell meal to rid the soil of nematodes. (The shell of the infinitesimal nematode eggs contains chitin, and chitinase is a substance that destroys chitin. Shrimp shells, crab shells, and lobster shells contain chitinase, thus it is thought that by adding shrimp shell meal to the soil one can disrupt the life cycle of nematodes. But regardless of why it happens, I know it works. Shrimp shell meal really does rid the soil of nematodes. Peaceful Valley Farm and Garden Supply is one purveyor.)

Thank you so much for your kind comments and I would love to meet you if you come to one of my talks. This reminds me I should post my talks for next year. A couple of years ago I decided to give talks just two months of the year, March and September, but I do intend to continue doing talks as long as I have my marbles. Every year I speak at Rogers Gardens in Corona Del Mar and they are kind enough to schedule this date in March, sometimes on the opening day of their spring garden show. Beyond that I am scheduled to speak in fall at the Master Gardener Seminar in Orange County which usually takes place at the Central Library of Redondo Beach, so that will be sometime in September 2012. On the seventh of March I will be speaking at 7:00 p.m. in San Clemente and on the first weekend in March I will be speaking at the Del Mar Fairgrounds, but that is a long way for you to come. I will post all these and more as they come in on my website well in advance of the dates.