Seed Starting Chart for Vegetables Grown at the Georgeson Botanical Garden

by Grant Matheke

This list has been developed over many years as a guide for seed germination of vegetables we have grown at the Georgeson Botanical Garden. These guidelines have been refined to adjust to our unique conditions in the greenhouse and in the garden. Your own growing conditions, especially light levels and temperature will be unique. Use this information as a starting point for your own list and take notes on germination rates and times to determine appropriate timing for your conditions. Plants that are too large at transplanting suffer greatly from transplant shock and those that are too small may not produce the plant you are hoping for. The calendar is timed for a field planting date of June 1 for warm season crops such as cucumbers and peppers, and May 20-25 for cool season crops such as broccoli. Check the chart for sowing of direct-seeded crops such as radishes, turnips.

Growing seedlings in the greenhouse or indoors is usually a two-stage process, sowing and transplanting. For most vegetables, we sow seeds into 4-inch pots (up to 50 seeds per pot depending on the size of the seed) or sow them singly into plug trays containing a very fine, sterile, peat-lite seed starting mix. We use additional seed starting mix or fine, horticultural grade vermiculite to cover seeds except those requiring light, so they are surrounded by moisture. We moisten the mix, cover the pots with clear plastic, and germinate them beneath lights with a thermostat-controlled heating mat beneath the pots to provide the optimum temperature. One pot holds a thermometer so we are measuring the medium temperature, not the air temperature. You can grow seedlings in cool rooms as long as the medium temperature is optimum.

As soon as seedlings are large enough to handle, we allow the peat-lite mix to dry a bit then gently tease apart the seedlings and transplant them into cell packs or larger pots using a coarse, peat-lite growing mix. The fine seed starting mix provides the best medium for germination of seeds but is too fine for continued growth. Seedlings easily rot if kept in this mix too long.

Some seedlings do not tolerate transplanting, so we have a one-stage procedure.  We skip the seed starting mix and sow them directly in cell packs using the growing mix. They include cucumbers, pumpkins, squash and lettuce. All seedlings are grown in a well lighted cool greenhouse, approximate minimum temperature 60-65F,  until ready to move outdoors.

One week before the planting date, we begin hardening off the seedlings. Hardening is a process of gradually exposing the seedlings to strong outdoor sunlight and cool temperatures. We set the flats outdoors for 1 hour on the first day, 2 hours, the second, then 4, 6, 8 and 10 hours on subsequent days. After that, the seedlings stay outdoors until transplanting.

Date

Name

Temp. F

Cover seeds

Days to Germination

Comments

27-Feb

Onion

70-75

y

10-14

transplant singly into cell packs

12-Mar

Chives

60-70

y

10-14

transplant in clumps into cell packs

12-Mar

Garlic chives (Chinese Leek)

60-70

y

10-14

transplant singly into cell packs

12-Mar

Leeks

70-75

y

10-14

transplant singly into cell packs

21-Mar

Brussels Sprouts

70-75

y

10-14

transplant into cell packs

21-Mar

Cabbage, Flat Top (O-S Cross)

70-75

y

10-14

seedlings are large; transplant into 6-inch pots to allow for good root growth

21-Mar

Celery

70-75

y

21-25

transplant into cell packs

21-Mar

Eggplant

70

y

10-15

transplant into 3- inch pot

21-Mar

Tomato (basket)

70-75

y

5-8

transplant into 3- inch pot

2-Apr

Artichoke

60-70

y

12-15

transplant into 3- inch pot

2-Apr

Pepper

75-80

y

10

transplant into 3- inch pot

16-Apr

Lentil

70-78

y

?

transplant into cell packs

16-Apr

Melons

75

y

5-7

sow into cell packs, transplant into 4 inch pots

16-Apr

Tomatillo

70-75

y

7-14

transplant into 3- inch pot

16-Apr

Tomato

70-75

y

5-8

transplant into 3- inch pot

23-Apr

Broccoli

70-75

y

8-10

transplant deeply up to leaves, grow cool

23-Apr

Cabbage

70-75

y

8-10

transplant deeply up to leaves, grow cool

23-Apr

Cauliflower

70-75

y

8-10

transplant deeply up to leaves, grow cool

25-Apr

Lettuce

65-70

n

7-10

Sow in cell packs, do not transplant; sow 3 seeds cut 2 out

25-Apr

Raddichio

65-70

n

7-10

Sow into cell packs, do not transplant

25-Apr

Sorrel

65-71

y

7-11

transplant into cell packs

30-Apr

Pumpkin

70-75

y

7-10

sow into cell packs, transplant into 4 inch pots

30-Apr

Squash, Winter

70-75

y

7-10

sow into cell packs, transplant into 4 inch pots

7-May

Cucumber

70

y

7-10

sow into cell packs, transplant into 4 inch pots

7-May

Squash, Summer

70-75

y

7-10

sow into cell packs, transplant into 4 inch pots

Direct

Bean

68-75

y

5-8

Do not direct dsow until soil >55F

Direct

Beet

72

y

7-10

Sow about 1 week before the last frost

Direct

Carrot

58-68

y

7-14

Sow about 1 week before the last frost

Direct

Greens

70

y

10

Sow about 1 week before the last frost

Direct

Kale

70

y

10

Sow about 1 week before the last frost

Direct

Kohlrabi

70

y

10

Sow about 1 week before the last frost

Direct

Lettuce, Leaf

70

y

5-7

Sow about 1 week before the last frost

Direct

Pak Choy

70

y

10

Sow about 1 week before the last frost

Direct

Parsnip

68-70

y

21-25

Germinates slowly, low %, sow heavily. Sow about 1 week before the last frost

Direct

Pea

70

y

7-10

Sow about 1 week before the last frost

Direct

Radish

70

y

10

Sow about 1 week before the last frost

Direct

Rutabaga

70

y

10

Sow about 1 week before the last frost

Direct

Spinach

65-68

y

8-10

Sow about 1 week before the last frost

Direct

Sweet Corn

70-75

y

7-10

Sow as soon as soil can be worked in the spring. Cover with clear plastic or IRT Mulch.

Direct

Swiss Chard

68-72

y

10-15

Sow about 1 week before the last frost

Direct

Turnip

70

y

10

Sow about 1 week before the last frost