So what I have been calling “succession planting” all these years is really “consecutive planting”. Succession planting is when you follow one crop with another, totally different crop, e.g., a sort-lived and cold-tolerant crop of radishes followed by a crop of carrots in the same place. Consecutive planting, is, to paraphrase Mother Earth News, replanting at periodic intervals. “Sow radishes and spinach once a week; sow beans, beets, carrots, scallions, and salad greens every two weeks; sow cucumbers and summer squash once a month. Since you can’t tell in advance just how warm or cool the season will be, keep planting until seeds stop sprouting well.”
Still, though, the world is imperfect and these terms are easy to confuse and I’ve found even the best and most trusted garden guides using them interchangeably (see the RHS, below, for example).
Consecutive sowing (and successive sowing, for that matter) isn’t ideal for every crop. It is best suited to salad-type crops with short lives: radishes, lettuces, rocket, spinach, and green onions. You can pull it off, to some extent (depending largely on climate and variety) with plants that have a medium lifespan, like cucumbers, but you can usually only get two batches, rather than a constant supply, which is the goal of consecutive sowing. Crops that take a long time to mature, like garlic, leeks, and Brussels sprouts, are not candidates for this trick. To get more of these guys you will need to use other methods: multiple varieties (with varying maturation rates), cold frames, green houses, row covers, etc.
The advice I’ve generally gotten on consecutive planting comes from the back of seed packets and invariable runs like this: plant again every two weeks until frost. This works OK (when I remember to do it), but (and you knew there was a but) there is a better way. You may have noticed, if you have tried consecutive planting, that germination rates are different depending on when you sow. The range on the back of the packet may be 7-14 days; if you sow consecutively you will see why: in the early, cool months of spring your sprouts will struggle to emerge within 14 days. When the soil is warm, the sun hot, and the days long, they may leap out as early as 5 days, just to show off. So planting every two weeks isn’t necessarily the most efficient method. The Royal Horticultural Society advises: “Rather than sowing every fortnight automatically, it may be wise to make new sowings when plants from the preceding sowing are well-developed. As a rough guide, this is when leafy crops have about four true leaves, when peas are 5cm (2in) high and beans about 10cm (4in) tall.” And the Duluth Community Garden Program puts it this way: “make the [first consecutive] plantings about 3 weeks apart. Sometime in late June reduce the span to 2 weeks for the next few plantings. Try your last two plantings about a week apart – maturity times are increasing rapidly in late summer/fall.”
Excuse me while I pull on my wellies and put my new-found understanding of consecutive planting to work.
 Damerow, Gail. “14 Ways to Extend Your Growing Season“. Mother Earth News, June/July 1994.
 “Successional Sowing“. Royal Horticultural Society website, accessed 05/26/13.
 Rosen, Joel. “Consecutive Planting”. Community Gardener’s Companion: The Newsletter of the Duluth Community Garden Program, Summer 2010.