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Succession Planting (or "Don't Stop Now") - Part 2
(see eNewsletter #21 for part 1)
by Steve Peters

Memorial Day weekend has come and gone, and homeowners throughout North America have followed a time-honored tradition. Over these hallowed three days, gardens are duly planted, and then often ignored (except for weeding, of course!) until early August, when the harvest season commences. In fact, as we gardeners know, the gardening season never stops, and we all have favorite strategies to get our plants in early to maximize the season. But let's not forget that there are many opportunities later in the summer to continue planting all kinds of crops and reaping those harvests for many months to come.

It is true that summer annuals (crops sensitive to frost) requiring 100 or more days to maturity have a limited planting window that ends, for the most part, by mid- to late June—summer solstice time, if your first fall frost date is some time in October. This would include all tomatoes, peppers, and eggplant (all from transplants), melons, and most corn, bean, squash and pumpkin varieties. Almost all other vegetables, however, have extended planting seasons that, in some crops, can last all summer long. For successful production, the most important factors to remember are: 1) your first average fall frost date, 2) days to maturity (from direct seeding or transplanting) of the specific variety you are sowing, and 3) whether the plant is frost-tender or frost-tolerant.  In addition, as the summer progresses toward mid- or late August, the day length begins to shorten noticeably, and the number of useful daylight hours for ripening a plant also lessens. For example, lettuce planted in mid-May may require 55 days to form a full head, but that same lettuce variety planted in mid-August may require 70 days to form a full head, because there are many less hours of effective sunlight in September and October compared to June and July.

The following is an approximate guide for planting opportunities after the summer solstice (June 21) for our common garden vegetables, if the average first frost date is mid-October. Adjust accordingly for earlier or later first frost dates in your area.

Last Planting: Early to Mid-July
  • Bush Beans - many varieties are ready in 50–60 days and can be planted until mid-July; late plantings avoid the ravages of the Mexican Bean Beetle
  • Broccoli - direct seed into a well-prepared nursery bed, and then transplant throughout the garden when seedlings are 4–6 weeks old
  • Cabbage - same as broccoli; however, varieties over 90 days to maturity may not reach full maturity if planted in July
  • Chinese Cabbage - same as broccoli
  • Cauliflower - same as broccoli
  • Corn - plant only varieties such as Hookers or Triple Play that mature in 60–70 days.
  • Cucumber - the longest maturing varieties require 75 days
  • Chicory - leaves can be harvested in 60–70 days, or roots can be harvested in 100 or more days
  • Okra - loves the heat, and matures quickly
  • Leeks - from transplants
  • Radicchio - same as chicory
  • Rutabaga - a cold-hardy root that requires a fairly long, cool season for best results
  • Summer Squash - great for quickly filling in empty spots in a mid-summer garden

Last Planting: Late July–Early August

Last Planting: Mid–Late August

  • Beet - if grown with protection such as a cloche or hoop house, can be planted well into the fall season
  • Beetberry - vigorous cool-season re-seeder produces tasty spinach-like leaves and mildly sweet berries
  • Broccoli Raab - same as broccoli above
  • Endive - wait until the end of August as soil temperatures begin cooling, and keep soil moist for best germination results
  • Lettuce - plant every three weeks throughout the summer for continual harvests; can be planted in September but yields decline significantly
  • Mustard - sow in nursery bed and then transplant throughout the garden
  • Orach - germinates in warm soils but thrives in cool weather
  • Purslane - can be planted all summer when soil temperatures are warm
  • Spinach - planting at this time produces tasty greens in October
  • Turnip - fall roots are extra sweet

Last Planting: Early–Mid September

  • Arugula - versatile, quick green that will re-seed and emerge early the following spring
  • Cress - rapid-growing green that can be planted throughout the winter if grown under cloches or a hoop house
  • Huazontle - tasty, vigorous green related to lambsquarter (Chenopod family) that also produces nutritious seeds if planted earlier
  • Komatsuna - quick-maturing Asian green that can be planted in nursery bed and transplanted like other brassicas (broccoli, kale, etc.)
  • Onion - in climates with minimum winter temperatures above 10º F (Zone 8 and warmer), short–mid day length-adapted varieties such as Riverside and Valencia can be planted throughout the southern U.S; long day length-adapted varieties such as Siskiyou Sweet can be planted in western Oregon and Washington
  • Radish - quick-growing roots have milder flavor in cool soils
  • Spinach - planting at this time produces small plants in the fall that go dormant during the winter and resume growing in early spring; harvest begins in late March, assuring continual production throughout the spring

Most of the common summer annual flowers that require warm soil temperatures for germination can still be planted until the end of June. When planted late, however, the bloom season is limited to the last few weeks before the fall frosts. These species would include Amaranth, Celosia, Coreopsis, Cosmos, Daisies, Marigolds, Morning Glories, Strawflowers, Sunflowers, and Zinnias.

In a climate where the minimum winter temperatures are above 0º F (Zone 7 or warmer), many annual flowers that are particularly cold-hardy may be planted during the last month of summer (August 20–September 20). Some species, notably Larkspur, Bachelor Buttons, and Nigella, will even overwinter in Zone 5. These plants will begin growing during the fall, stop growing during the winter, and resume growth the following spring as soil temperatures rise. It is recommended to cover the young plants with straw or leaf mulch during the winter, although this may be unnecessary if winter conditions are mild.

The most reliable and well-known flower species that can be planted during late summer for early blooms during the subsequent spring include Bachelor Buttons, Calendula, Flax, Larkspur, Nigella, Snapdragon (actually a biennial or short-term perennial in very mild-winter regions), and Sweet Pea. Other species that may over-winter successfully if conditions are favorable, although not as reliably as the previously-listed species include Alyssum, Agrostemma, Borage, Cleome, Lavatera, and Scabiosa.

There are also a few annual or biennial herbs that are quite winter-hardy and can be late-summer planted and will survive the winter in regions in Zone 7 or warmer. These herbs include Cilantro, Dill, Fennel, and Parsley. It is worth trying these in colder climates too, especially if you have protected microclimates in your garden. A south-facing wall or even a boulder to hold the sun's warmth can make a difference.

Another opportunity for summer planting involves most of the perennial flowers. These plants are typically started in greenhouses during the winter. Those of us without a greenhouse, however, can prepare a nursery bed in our garden specifically for direct seeding of perennials during the summer. It is important to keep the bed free of weeds, as most perennials are very slow growing and are not competitive with fast-growing annual weeds. Be sure that your nursery bed has adequate irrigation and has at least average fertility. Plant your perennial seed at least ten weeks before the first fall frost to allow for the plants to become established before the onset of winter. The following summer, when the plants are one year old, it will be time to move these plants from the nursery bed to their permanent location in the garden. The most common perennial flower species that would be suitable for this type of propagation would include Anthemis, Bergamot, Campanula, Columbine, Shasta Daisy, Delphinium, Echinacea (requires 60–90 day cold stratification for germination), Foxglove, Gaillardia, Hollyhock (actually a biennial), Lobelia, Penstemon, Pinks (Dianthus), Evening Primrose, Rudbeckia, Salvia (many species), Snapdragon, and Yarrow (Achillea).

Planting seeds throughout the summer means that we can enjoy a bountiful harvest for a much longer time, but it also is significant in other ways. As gardeners, we are often limited for space, so it is important to maximize every square foot of available soil area. In essence we are trying to capture the greatest amount of solar energy possible in the space available to us. The best way to do this is to have 100% coverage of your garden's surface area at all times. From the information above, it should be clear that there are many plants that continue to grow and thrive throughout the summer and fall and early spring seasons. By growing different species together, no soil surface is left bare. This maximizes soil cover, intensifies soil biological activity and above-ground insect activity, and increases overall plant yields. Of course, it is essential to maintain fertility in such an intensive system, so keep that compost pile going!

The following are examples of crops growing together simultaneously for at least part of their life cycle:

  • Sowing buckwheat between tomato plants keeps weeds suppressed, adds carbon to the soil, and improves soil structure. The buckwheat can be mowed with a Kama (hand sickle) before it competes with the tomatoes and left as mulch. This technique also works well with squashes and cucumbers, which have lots of bare soil around them as they develop. If you use floating row cover to control pests, the buckwheat can actually lift the row cover off the plants. Remove the row cover when the squash flowers and again, cut the buckwheat and leave as a mulch.
  • Transplanting lettuce into a stand of broccoli (or other brassicas such as kale or cauliflower) maximizes available garden space of two species that have different plant architectures but similar growing requirements. The lettuce is harvested as the brassica plants fill in, having acted as a living mulch to suppress weeds and hold soil moisture. The brassica plants also provide a little protection for the lettuce as it develops.
  • Planting radishes and carrots together allows for an early harvest of radishes followed by a later carrot harvest. The radishes also help to mark the slower germinating carrot rows so an early cultivation can be done before the carrots emerge.

There are many more examples of inter-planting for maximum production. Quick-growing plants such as radish, arugula, or cress can be sown into already-established beds of tomato, pepper, corn, or beans. Plants that are easily transplanted such as brassicas, greens, or basil can be planted into open spots throughout the garden to insure that no space is wasted. The primary limitation is the availability of water. If water is available, the only limitation is your own imagination!

The tradition of planting everything on Memorial Day and then calling the garden planted is really a myth. The far more ancient traditions of gardening cultures, such as China's, follow a sequential planting much like that outlined above. Many Asian vegetables, for example, are bred to mature very quickly, and often do better when planted later in the season. In a society where arable land is scarce, gardening all year round is more than just an efficient system. It means that the people have enough to eat. So keep on sowing for a bountiful, beautiful garden, and an extended harvest of the finest food available, organically grown in your own backyard.

Steve Peters
Seeds of Change Product Development Manager

Photo Captions: (1) Lettuce utilizes the space between young broccoli transplants while providing a living mulch. As the broccoli grows. it provides shade for the lettuce, helping prevent bolting. (2) Buckwheat controls weeds and protects soil between tomato transplants (left) It took ten minutes to mow the buckwheat with a Kama and remove the suckers on all the tomato plants. (3) Heads of Reine de Glaces lettuce intercropped with onions to utilize space, protect the soil and control weeds. Onions will be sidedressed with compost as lettuce is harvested.http://counselinginannarbor.wordpress.com/

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