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When to Start Annuals Indoors

BY Kevin Lee Jacobs | March 3, 2010 7 Comments

Last updated on December 2nd, 2011


FLOWERING ANNUALS — like the pink petunias above — grow so readily from seed it is really extravagant to obtain them any other way. Most can be winter-sown outdoors; for extra-early bloom, however, I like to start at least some of the seeds indoors, under fluorescent lights. Here is a handy schedule for indoor-sowing:

INDOOR SEED-STARTING SCHEDULE FOR FLOWERING ANNUALS (Listed by weeks before average last spring frost)
Transplant seedlings to outdoor garden after the last spring frost; plants marked (*) can be transplanted after the last heavy frost

12 Weeks. Pansy*

10 Weeks. Snapdragon*; Sweet William; Zonal Pelargonium (Geranium); Lobelia; Impatiens; Ageratum

8 Weeks. Alyssum; Aster*; Bells of Ireland*; Calendula*; Celosia; Coleus; Cornflower (Bachelor Button); Dahlia; Marigold; Nicotiana; Petunia; Portulaca; Salvia; Stock; Sweet Pea*; Zinnia

6 Weeks. Cleome (Spider Flower); Four O’Clocks; Morning Glory; Nasturtium*; Sunflower

4 Weeks. Cosmos*

The National Climatic Data Center will tell you the average last frost date for your area. Here, in my Hudson Valley zone 5-b garden, that date is May 17.

Early bloom, endless variety, and tremendous cost-savings — these are just three good reasons to start your summer annuals indoors. And, growing your own rather than buying plants from a local nursery really makes you feel like a gardener. Well, a self-sufficient gardener, anyway.

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Comments

  1. 1

    James says

    March 3, 2010 at 4:10 pm

    Kevin, thanks for the schedule. I'm going to start petunias, marigolds and zinnias under lights this spring. Otherwise I spend waaaaay too much money at various garden centers.

  2. 2

    Adele says

    March 3, 2010 at 4:42 pm

    I can think of another great advantage for starting seeds indoors: you can avoid the dreaded flats of “mixed” colors that garden centers love to offer.

  3. 3

    Yolanda says

    March 3, 2010 at 10:48 pm

    Kevin, I have petunia plants that I overwintered. When should I take more cuttings to start new plants (I'd rather not grow them from seeds).

  4. 4

    Kevin Lee Jacobs says

    March 3, 2010 at 11:13 pm

    Adele – I'm with you on florist-sold mixed colors. Sometimes the effect is nice. But more often than not a single shade is more effective, and you can only have this with certain plants if you grow the seeds yourself.

    Yolanda – Now is the time to take your petunia cuttings. Insert these in any pot of light, porous soil. 4 cuttings per six-inch pot will produce a fairly substantial specimen.

  5. 5

    Roger Sachs says

    May 3, 2019 at 4:02 pm

    Planted Marigolds from seed. When can I begin fertilizing? They are about 3 weeks along with the 3rd leaf on most.

  6. 6

    Napmi says

    January 29, 2020 at 12:29 pm

    Hi, question : if I start growing zinnias and coleus from seed indoor now, what do I do with them once they are a little bigger? Do they need to stay under the grow lights all the way through spring until I’m ready to plant outside or can they be moved to a window once it has become more established? Thanks!

  7. 7

    Kevin Lee Jacobs says

    January 29, 2020 at 1:39 pm

    Welcome, Napmi – Coleus should be fine if placed in a window; be sure to pinch off new growth to encourage branching. I no longer start seeds of annuals under lights. Instead, I winter-sow them outdoors! Click here for details: Winter-Sowing 101.

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