When To Sow or Plant Out Your Annuals

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Annuals grow quickly, but die after they bloom. They leave seeds to start a new generation. Illustration: Twinkl

An annual is a plant that goes through its entire cycle of growth from seed to seedling to flowering to seed producer in a single season… and then dies. The seeds fall to the ground and sprout the following season (at least, that’s how things work in the wild) and the cycle continues

That was, however, the botanical definition of an annual.

We gardeners see things a bit differently. For us, an annual is a plant that is normally grown for one single season of use, even if we have to start it indoors to reach that point. Moreover, many garden annuals are actually biennials or perennials in their native lands… it’s just that we grow them as annuals, harvesting them or getting them to bloom the first year, then letting the cold kill them in the fall.

To know when to plant or sow an annual outdoors, however, it is helpful to know which type of annual you’re dealing with: a hardy annual, a half-hardy annual or a tender annual. So here are a few definitions:

Hardy Annuals

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The sunflower is a typical hardy annual: sow it outdoors… and stand back! Photo: xlibber, Wikimedia Commons

These are the classic garden annuals that our grandparents grew. You simply sow their seeds outdoors early in the season, when the soil is still cold, and they’ll flower easily that the same year. You can even sow hardy annuals outdoors in the fall and they’ll germinate the following spring, because their seeds tolerate long periods of cold.

Even after they germinate, hardy annual seedlings are very resistant to cold and will even tolerate a touch of frost. They’re the ones you can sow “as soon as the soil can be worked”. If you do start them indoors, you can transplant them into the garden 2 or 3 weeks before the last frost date (yes, you read that correctly: before the last frost date).

Here are some examples of hardy annuals. Note that quite a few of them, especially among the vegetables, are actually biennials treated as annuals by gardeners.

  1. Bachelor’s buttons, cornflower (Centaurea cyanea)
  2. Broccoli (Brassica oleracea italica)
  3. Brussel sprouts (Brassica oleracea gemmifera)
  4. Cabbage (Brassica oleracea captitata)
  5. Carrot (Daucus carota)
  6. Chervil (Anthriscus cerefolium)
  7. China pink (Dianthus chinensis)
  8. Coriander, cilantro (Coriandrum sativum)
  9. Dill (Anethum graveolens)
  10. Dusty miller (Senecio cineraria)
  11. Kale (Brassica oleracea acephala)
  12. Kohlrabi (Brassica oleracea gonglyoides)
  13. Larkspur (Consolida amibigua)
  14. Leek (Allium ampeloprasum)
  15. Love-in-a-mist (Nigella damascena)
  16. Onion (Alliium cepa)
  17. Ornamental cabbage (Brassica oleracea)
  18. Pansy (Viola x wittrockiana)
  19. Pea (Pisum sativum)
  20. Pot marigold (Calendula officinalis)
  21. Radish (Raphanus sativus)
  22. Rutabaga (Brassica napus napobrassica)
  23. Shirley poppy (Papaver rhoeas)
  24. Snapdragon (Antirrhinum majus)
  25. Spinach (Spinacia oleracea)
  26. Summer savory (Satureja hortensis)
  27. Sunflower (Helianthus annuus)
  28. Sweet alyssum (Lobularia maritima)
  29. Sweet pea (Lathyrus odoratus)
  30. Sweet William (Dianthus barbatus)
  31. Tall vervain (Verbena bonariensis)
  32. Turnip (Brassica rapus)

Half-Hardy Annuals

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The cosmos is a half-hardy annual: it tolerates cold temperatures, but not frost. Photo: Yoko Nekonomanica, Wikimedia Commons

These are annuals (or plants treated as if they were annuals) that tolerate cool temperatures, but not frost. In cold regions, you usually need to start them indoors, otherwise they are slow to come into bloom. You would normally transplant these ones outdoors at around the last frost date, thus when the soil and the air are still cool to cold, but there is no longer any risk of frost. In milder regions where the growing season is very long (hardiness zones 7 to 9), you can sow half-hardy annuals directly outdoors just as you would do with hardy annuals.

  1. African daisy (Osteospermum spp.)
  2. Beet, beetroot (Beta vulgaris crassa)
  3. Black-eye susan (Rudbeckia hirta)
  4. Carnation (Dianthus caryophyllus)
  5. Cauliflower (Brassica oleracea botrytis)
  6. Chinese cabbage (Brassica rapa pekinensis)
  7. Cosmos (Cosmos spp.)
  8. Edging lobelia (Lobelia erinus)
  9. Endive, chicory (Chicorium intybus)
  10. Fuchsia (Fuchsia spp.)
  11. Gazania, treasure flower (Gazania rigens)
  12. Lettuce (Latuca sativa)
  13. Mealy sage (Salvia farinacea)
  14. Mustard (Brassica juncea, B. nigra and others)
  15. Nasturtium (Tropaeolum majus)
  16. Parsley (Petroselinum crispum)
  17. Parsnip (Pastinaca sativa)
  18. Pelargonium (Pelargonium spp.)
  19. Petunia (Petunia spp.)
  20. Portulaca (Portulaca grandiflora)
  21. Potato (Solanum tuberosum)
  22. Swiss chard (Beta vulgaris cicla)
  23. Vietnamese coriander (Persicaria odorata)

Tender Annuals

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Like many fruit-bearing vegetables, the cucumber is fast-growing, but unable to take cold temperatures. Don’t hurry to plant it out.

Generally, tender annuals are not true annuals. In their countries of origin, most are perennials, but they are grown as annuals in cold climates. Most need to be sown indoors, although a few, notably cucumbers and squash, grow quickly enough that you can sow them outdoors. They don’t appreciate cool temperatures and should not be planted out until there is not only no longer any risk of frost, but until the soil and air have warmed up. Consider night temperatures of 5°F (10°C) to be an absolute minimum for tender annuals. In fact, 55°F (13°C) nights are even surer.

  1. Ageratum, flossflower (Ageratum houstonianum)
  2. Amaranth, love-lies-bleeding (Amaranthus spp.)
  3. Basil (Basilicum ocimum)
  4. Bean (Phaseolus spp.)
  5. Begonia (Begonia spp.)
  6. Castorbean plant (Ricinus communis)
  7. Celery (Apium graveolens)
  8. Celosia, cockscomb (Celosia argentea)
  9. Coleus (Plectranthus scutellarioides)
  10. Corn, mays (Zea mays)
  11. Cucumber (Cucumis sativus)
  12. Eggplant, aubergine (Solanum melongena)
  13. Hybrid vervaine (Verbena x)
  14. Impatiens (Impatiens spp.)
  15. Marigold (Tagetes spp.)
  16. Melon (Cucumis melo)
  17. Nicotiana, flowering tobacco (Nicotiana alata and others)
  18. Okra, gombo (Abelmoschus esculentus)
  19. Salvia, scarlet sage (Salvia splendens)
  20. Squash, pumpkin, vegetable marrow (Cucurbita spp.)
  21. Tomato (Solanum lycopersicum)
  22. Watermelon (Citrullus lanatus)
  23. Zinnia (Zinnia spp.)20170530A ENgl Twinkl
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