Many vegetable crops can be planted several times during the season to provide a continuous supply. Because the length of time from sowing to harvest varies according to temperature (and daylength, in some cases), simply planting squash once a month, for instance, will not provide an even supply. By keeping records, and using information from other growers, you can fine-tune your planting dates for better results.

Our first effort along these lines involved keeping a “Veg Finder”, a chart where we note planting date, first harvest and last harvest. (“Veg” is the British abbreviation – you might prefer “Veggie”). We use this for bush beans, summer squash, cucumbers, sweet corn and carrots. (We have a similar chart for lettuce, which is a whole exercise of its own). The original aim of the Veg Finder was to alert crews about which plantings were currently ready to harvest and where to find them. After keeping these charts for a few years we could use the information for improving our planting dates.

Most growers are probably adept at planting as soon as possible in the spring. A lesson for me has been not to plant too early! Keeping aged cucumber transplants alive through cold early spring weather is just not worthwhile. I finally grasped this the year we planted our first and second plantings side by side, and the second ones did better than the first, and were ready just as soon!

It’s important to know what is the last date for planting each crop, that has a reasonable chance of success. For this last part we got help from a leaflet from our Extension Service: Fall Vegetable Gardening: www.ext.vt.edu/pubs/envirohort/426-334/426-334.html

The formula (for frost tender crops), for figuring the number of days to count back from the expected first frost date is: add the number of days from seeding to harvest, the average length of the harvest period, 14 days to allow for the slowing rate of growth in the fall, and 14 days to allow for an early frost. For example, yellow squash takes maybe 50 days from sowing to harvest, and is good for 21 days, so the last date for sowing would be 50+21+14+14= 99 days before the first frost. For us in central Virginia, that means 99 days before October 14th, or July 7th. But with rowcover to throw over the last planting on frosty nights, it’s possible to act as if the growing season is 2 weeks longer, and ignore the 14 days for an early frost. And so our last planting of squash is August 5th.

The three pieces of information: first planting date, last planting date, and number of productive days of a planting, enable us to make a rough plan for how often to plant. For us the rough version is every two weeks for beans and corn, every 3 weeks for squash and cucumbers, once a month for carrots, and two plantings of muskmelons at least a month apart.

Recordkeeping
There are methods of succession planting that involve no paperwork. For example, sow another planting of sweet corn when the previous one is 1-2” tall; sow more lettuce when the previous sowing germinates. Another approach is to sow several varieties with differing days-to-maturity on the same day. We sow Bodacious, Kandy Korn and Silver Queen on the same day, and get more than two weeks of plentiful harvests.

But for the fine-tuning for a really even supply of crops, nothing beats having real information about what happened, written at the time it happened! Our system for gathering crop records consists of a 3×5 spiral notebook I carry all the time, an 8 1/2 x 11 spiral notebook (with pages flagged with sticky notes for each crop), and a ring binder with alphabet dividers to store the information at the end of the year. I transfer the field notes from the small to the larger notebook sporadically during the season, and then have long filing sessions on rainy days in late fall and early winter. We hold a crew Crop Review Meeting in November, and then do garden planning in December and January, taking the lessons learned into account.

Graphs show results at a glance
Having graphs of sowing and harvest dates for each crop has been very useful for planning effective planting dates. Graphs can be done on blue-squared paper, graph paper or spreadsheet programs. We plotted graphs for each crop, of sowing date along the x axis and first harvest date along the y axis. The Veg Finder gave us the information on how long the harvest period is for each crop, so we could decide how frequently we needed to have a new patch be ready to harvest. If you don’t have your own crop records yet, you can use our graphs as a jumping off point. Because of space constraints, we can’t reproduce them in this article, but they are available on the Growing for Market web site. Go to www.growingformarket.com and choose Follow Up from the buttons on the left. Under May 2006 you’ll find a link to the information.

The spreadsheet program I use is Excel, and it doesn’t seem to recognize the word “graph”, preferring “chart”. So I start the worksheet by entering two columns, one for sowing date and one for first harvest. I have information from several different years with varying sowing dates, rather than results from sowing on every day in the season. The Chart Wizard calls this type, with irregular intervals between entries a “scatter chart”. I use the chart subtype that has marked data points joined by a smoothed line. I follow the four-step process and position the chart in the worksheet with the columns of sowing and harvest dates. The line of the graph is often rather uneven, due to differences in weather from year to year, and to growing varieties with differing maturity dates. This is about as precise as I’m prepared to get, so I just pencil in a more even line, and use that to derive my sowing dates.

Here’s what we have learned about succession planting various crops:

• Summer Squash and Cucumbers. Information from the graphs may help you find you can plant less often than you thought. We used to do six plantings of summer squash and cucumbers: 3/25 (transplanted 4/20), 5/14 (transplanted 6/7), 6/13, 7/3, 7/19 and 8/5. The intervals between these sowings are 50, 30, 20, 16 and 17 days. By using the graphs, we have been able to reduce to five plantings: 3/25 (transplanted 4/20), 5/24, 6/23, 7/15, 8/5. The intervals are 60, 30, 22 and 21 days. There are several notable features of these changes. The sowing intervals decrease as the season warms up, as it takes fewer days for plants to mature. The first planting is very slow to mature – probably we could just start later still, and lose nothing. By moving the second planting 10 days later, we are able to direct sow rather than transplant, which saves us time. This revised schedule saves us from dumping zucchini on our neighbors’ porches!
  Cucumbers take longer to mature than squash, but after looking at the graphs, we decided to plant both on the same set of dates, for simplicity. For us, squash plantings stay productive for around six weeks, while cucumbers only last four or five weeks. We are often picking from two plantings on the same day – the overlap helps even out our supply, as the dwindling old patch augments the newly starting row. If we could be satisfied with a new patch coming on-stream every four weeks, we could sow only 4 times: 3/25, 5/29, 7/3, 7/28.
• Beans. Other factors can affect sowing dates for succession crops too. We used to be sorely plagued by Mexican Bean Beetles. This meant that pole beans were a complete waste of time (they didn’t mature before the beetles ravaged them), and we needed a new patch of bush beans every 2 weeks to keep up supplies. We made 7 plantings at 15-day intervals: 4/16, 5/20, 6/9, 6/24, 7/9, 7/22 and 8/3. After 2 weeks of harvesting each planting, we would need to do “Root Checks”, our euphemism for pulling up the beetle-ridden plants, picking off the last beans, and taking the plants off to our (fairly distant) composting area. Now we buy the parasitic pedio wasp. We get ours from Biconet in TN: www.biconet.com. When we see the first larvae, we order 1 unit/400 square feet of the first planting. The parasites (Pediobius foveolatus) arrive as mummified bean beetle larvae on the point of hatching. We set the open container under the bean leaves, and in a week or so, we start seeing brown shriveled larvae on the leaves. Until then, we do need to handpick the adult beetles to get the level down to 1 beetle per 3 ft. of row, so the larvae numbers will be manageable for the parasites. Once the parasites are established for the season, there’s no more need for hand picking, and the second and subsequent plantings will look very healthy. The adult pedio wasps can fly up to 20 miles, so your neighbor bean growers will be grateful too!
  
  Adjusting our planting plans has helped maximize success. The spring emergence of adult MBB occurs in the area where the last planting was the previous year, so if we make a small, early planting in this area, we can buy just 1 or 2 units of pedio wasps, which can quickly get to work for us. We plan larger plantings from the second onwards. There is a more exact plan, which I haven’t tried: put the production planting as far distant as possible from a first, short (trap crop) row but only a week later. Before the trap crop larvae pupate, flame that row to destroy it. Later the same day, release the parasites in the production row.
  
  We now plan for a new patch to harvest every 20 days, sowing 6 times rather than 7: on 4/16, 5/14, 6/7, 7/19 and 8/3. These sowing intervals are 28, 28, 22, 20 and 15 days. We also get more beans than previously. If we needed only the smaller quantities, we could sow 5 times: 4/16, 5/26, 6/20, 7/2 and 8/3. This would give us a new harvest starting every 21 days, almost as often as our 6 plantings. However, we like the bigger quantities, so we pick from two patches for an overlap period, a lot of the time.
  There is a listing of suppliers of beneficial insects in the United States at: www.cdpr.ca.gov/docs/ipminov/bensuppl.htm
• Hoophouse Crops: Two seasons ago, we added a 30’ x 96’ hoophouse. We plant our earliest squash and cucumbers in there. We are still figuring out the fine-tuning on this. I think we could eliminate our chancy early outdoor plantings, and reduce our stress without losing much yield. We sow cucumbers 2/14 (we like General Lee for its compact vines and prolific cucumbers) and squash 3/1 (Zephyr has become a favorite) and transplant 4/1, for harvests starting 5/19 (squash) and 5/21 (cucumbers).
• Lettuce: Succession planting of lettuce, because it is such a fast turnaround crop, is a subject in its own right. The short version is that we sow twice in January, twice in February, every 10 days in March, 9 in April, 8 in May, once a week in June and July, then every five days in early August, moving to every three days in late August, and every other day until Sept 21. After that we ease back out to every three days until the end of September or early October. Those last plants will feed us right through the winter.
• Sweet Corn: We have been in the habit of making seven plantings: 4/26, 5/17, 6/2, 6/16, 6/30, 7/14 and 7/28. The intervals are 21, 15 and then 14 days. Last year, because of shortage of space, we eliminated the 7th sowing, and increased the size of the 6th, planting a range of three varieties, as noted above. The season did finish a bit earlier than usual, but we got no complaints. The 7th sowing has always been a risky one. Using the graph of our corn sowing and harvest dates I made while writing this article, I estimate that 4/26, 5/19, 6/6, 6/24, 7/7, 7/16 and 7/23 would be good dates to provide fresh eating every two weeks. The planting intervals are 23, 18, 18, 13, 9 and 7 days. This calculation is a “live performance”, not a tested schedule!
• Carrots: We sow mid-late February, starting as early as possible. Then we sow 360 row feet every four weeks in March, April, May, and if needed, in June and July. We avoid these hot weather sowings if we still have spring carrots in the cooler, as the flavor of hot weather carrots is not very good (Nelson has been the tastiest for us), and we may get Alternaria blight, which turns the leaves black and so reduces growth. We make a huge fall planting in late July or early August. If we miss those dates, we wait till late August to avoid the high numbers of grasshoppers here in mid-August. Late August sowings don’t bring as heavy yields as the earlier ones, unless the winter weather lets us harvest later than usual.

Resources
ATTRA Scheduling Vegetable Plantings for a Continuous Harvest. This is available online, http://attra.org/attra-pub/continuousharvest.html but there are valuable enclosures that are unobtainable online for copyright reasons, so call them at 800-346-9140 and ask for a printed copy. There is no charge. ATTRA Market Farming: A Start Up Guide. http://attra.org/attra-pub/marketgardening.html

Pam Dawling manages the vegetable garden for Twin Oaks Community in Louisa, Virgnia. She can be contacted at pam@twinoaks.org.