Thursday, August 9, 2012
A quick lesson in crop planning
We are often asked why we grow so much lettuce, chard and kale, but not more mizuna, arugula, broccoli or cauliflower. Why not more carrots and onions? To answer this question requires a general overview of crop planning and rotations in organic agriculture.
When we grow a crop in a particular bed, organic standards (and best practices) require that we don’t grow another related crop in the same area for three years. By rotating our growing spaces in this way, we are able to break or disrupt disease and pest cycles without the use of chemical pesticides.
It also supports a better nutrient management plan. In the first year of a rotation, we might grow a heavy-feeder that requires a lot of compost. This could be squash, onions, leafy greens, corn or broccoli. The second year, we will grow carrots, which don’t need as much fertility, thus eliminating the need to compost again. The third year we can grow potatoes, which need very little nitrogen, thus no compost again – perhaps only a bit of potassium and calcium, which can be added separately. In the fourth year we can grow beans, which have a symbiotic relationship with microbes that fix nitrogen for the plants – no compost again!
In an ideal rotation, we include cover crops (like oats, rye, barley, clover and vetch) over the winter to add organic matter and, in some cases, fix nitrogen. Some grain crops scavenge nutrients in the soil and hold them until they are tilled in (rather than the soil leaching nutrients during the winter rains); as they break down, the nutrients are available to the next crop and also feed soil organisms.
So, back to the crop families. When we grow a bed of kale (of the brassica family in plant talk), we can harvest from the same plants repeatedly throughout the season. We get our first harvest within 1-2 months after transplanting. A small space yields a tremendous amount of food over the subsequent 8-12 months.
Broccoli and cauliflower, on the other hand, yield one harvest. The plants grow for 2-3 months before producing one crown.
One bed of kale in our fields can yield $5,000 over the course of the season; one bed of broccoli yields about $850. After the harvest, neither bed can be used for anything in that family for three years. Kale is abundant; that’s why we take lots to market and include it in CSA boxes regularly. It's hard to make money off of Broccoli and it has to fight for space with everything else in the same family.
In another example, lettuce is not related to much else that we grow. It takes 45 days to mature from transplanting. We can often get one or two subsequent crops into a lettuce bed after harvest. Even though a bed of lettuce may yield only $1500 in revenue, the bed space yields higher returns because it can be triple-cropped in a season.
So, finally, in case you are curious about which crops are related, here’s a quick cheat-sheet:
• Brassicaceae: Kale, collards, broccoli, cauliflower, mizuna, arugula, turnips, rutabaga, cabbage, Brussels sprouts, gai land, bok choi, kohlrabi
• Cucurbitaceae: Squash, melons, cucumbers
• Solanaceae: Potatoes, Tomatoes, Eggplants, Peppers
• Chenopodiaceae: Chard, Beets, Spinach, Quinoa
• Apiaceae: Carrots, Parsley, Fennel, Dill, Cilantro, Parsnips, Celery
• Asteraceae: Sunchokes, endives, chicory, radicchio
• Alliaceae: Onions, shallots, garlic, green onions, chives, leeks
• Fabaceae: Beans, peas
This is what we juggle when planning our crops!