Quick Facts...
- Some annuals are best seeded directly in the garden in spring..
- Cold frames allow starting plants as much as six weeks before planting-out
time.
- Do not start plants too soon — they may become crowded and spindly
before they can be planted safely outdoors.
- Plants grown early indoors or in cold frames need to be exposed to
the outdoors gradually to avoid shock.
Preparation
Before seeding, spade the garden area 6 to 10 inches deep. Thoroughly
mix in coarse peat, compost or aged manure if the soil is too heavy (clay
type) or too sandy. Use 3 cubic yards of organic matter per 1,000 square
feet or enough to cover to a depth of 1 inch.
The organic matter helps keep the soil from becoming too compact and
holds moisture needed for seed germination. Rake the surface smooth and
remove or break down clods larger than the size of a pea. Plant seeds
in rows and cover with a fine soil to the depth indicated on the seed
packet. Mark the seeded rows with identifying labels.
Use good, viable seed. Seed saved from last year’s garden rarely
results in the flower colors desired because of interbreeding of varieties.
Old seed, unless carefully stored in a cool, dry location, often germinates
poorly. It is usually more satisfactory to buy fresh, new seed when growing
garden annuals and vegetables. Most seed packets are dated using phrases
such as “Packed for (Year).”
Sow seed directly in the garden for the simplest way to start plants.
It is usually safe to sow the seed outdoors when trees are beginning to
produce leaves. See Table 1 for when to start seeds of specific plants.
Keep the seedbed moist at all times. When seedlings appear, thin plants
to half the height they are supposed to attain, except for tall, spike-like
annuals such as snapdragons, larkspur and foxglove. Thin these to one-fourth
their mature height for a fuller, more showy effect.
Cold Frames
For an early start, sow seed in a cold frame and transplant it into the
garden later (see Figure 1). Seed may be started as much as six weeks
earlier than outdoors.
Locate the cold frame on the south side of a garage or dwelling. If built
with a tight-fitting lid, the cold frame will hold sufficient heat from
the sun to keep seed and seedlings warm at night. On warm, sunny days
(50 degrees F or warmer), prop the lid open to prevent buildup of excessive
heat. Close the lid in the late afternoon to trap enough heat for cold
evenings.
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Figure 1: A simple cold frame made with 2-inch x 2-inch lumber. Cover hinged lid and sides with translucent (clear) polyethylene plastic. For better insulation against cold, cover both inside and outside to leave an airspace between layers of plastic. An 8-foot frame requires 10 pieces 2 inches x 2 inches, each 8 feet long.
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If temperatures fall below 20 degrees, an outdoor-type electric light
may be placed in the box to produce enough heat to keep plants from freezing.
Insulated drop cords are suitable for this purpose. One 60-watt incandescent
bulb for every 12 cubic feet of cold frame space usually is sufficient.
Electric heating cables are available at most garden supply stores.
As the season progresses, gradually expose the plants to longer periods
of outside temperatures, as long as the air temperature does not go below
50 degrees. Treated in this way, they develop into sturdier plants that
are better able to adapt to fully-exposed garden conditions at transplant
time. This is particularly true of the hardy annuals and biennials that
prefer to develop in cooler temperatures: petunia, ageratum, lobelia,
verbena, cabbage, broccoli and lettuce. Use Table 1 to determine when
to start seed in the cold frame.
| Table 1: Starting times for seeds grown indoors and
in cold frames. |
|
Number of weeks to start seed
before average frost-free date.
|
| Plant name |
In cold frame
|
Indoors
|
| Ageratum |
6
|
8
|
| *Amaranthus (summer poinsettia) |
4
|
6
|
| *Bachelor’s button |
4
|
4
|
| Broccoli |
6
|
4a
|
| Cabbage |
6
|
4a
|
| *Calendula |
4
|
4
|
| *California poppy |
4
|
4
|
| Calliopsis |
4
|
6
|
| Cauliflower |
6
|
4a
|
| China aster |
4
|
6
|
| *Cosmos |
4
|
4
|
| Dahlia |
6
|
8
|
| Dimorphotheca (African daisy) |
4
|
4
|
| *Gaillardia |
4
|
4
|
| *Gomphrena |
4
|
4
|
| Larkspur |
4
|
6
|
| Lettuce (head and semihead) |
6
|
4b
|
| Lobelia |
6
|
8
|
| *Marigold |
4b
|
4
|
| *Morning glory |
4
|
4
|
| *Nasturtium |
4b
|
4
|
| Pepper |
4b
|
6
|
| Petunia |
6
|
8
|
| Phlox (annual) |
4
|
6
|
| *Poppy (Shirley) |
4
|
4
|
| Salvia |
4
|
6
|
| *Scabiosa |
4
|
4
|
| Snapdragon |
6
|
8
|
| Statice |
4
|
6
|
| *Straw flower |
4
|
4
|
| *Sweet alyssum (lobularia) |
4
|
6
|
| Tomato |
4b
|
6
|
| Verbena |
6
|
8
|
| Vinca (annual) |
4
|
6
|
| *Zinnia |
4
|
4
|
*Plants best suited for direct
seeding in garden two weeks prior to the average frost-free date.
aShould be kept in coolest room. Best at 55 to 60 degrees.
bIf outside temperatures are below 20 degrees at night,
delay planting or use artificial heat to keep temperatures above 50
degrees in cold frame. |
Starting Seed Indoors
If space is available near a sunny window, start seeds four to eight
weeks before the plant-out date in your area (average date of last killing
frost). Starting too early usually results in spindly plants due to crowding
and lack of sufficient light.
Almost any container with drainage holes in the bottom will work for
planting. Paper milk cartons cut in half, Styrofoam cups, tin cans, plastic
trays and pots are common containers used. For convenience, however, you
may wish to start plants in the plastic trays and pots available at garden
supply centers.
Use a rich, well-drained soil. Potting soils made for African violets
and other house plants usually are suitable and do not have weed seeds.
They are, however, more expensive than soil mixes you can make at home.
If you use soil from the yard, it should be top soil that is well drained
and not high in clay.
The best soils are often found around established shrubs and trees. Add
sphagnum peat and sharp sand to the soil in a ratio of about one-half
volume of each, and mixed thoroughly.
To kill weed seeds and some damaging soil fungi, place the soil mix in
shallow trays or baking pans in an oven for 45 minutes at 250 degrees.
For best results, the soil should be moist.
After the soil has cooled, fill containers firmly but do not pack. Allow
about 3/4 inch from the soil surface to the rim of the container. Place
seeds on the soil surface. Use a piece of window screen or old flour sifter
to sift soil over the seeds to the depth indicated on the seed packet.
If you use compartmentalized trays or individual peat pots, place two
or three seeds in each pot. Do not cover too deeply, as this may reduce
or prevent seed germination. As a general rule, cover no more than four
times the diameter of the seed.
Apply a fine spray of water to avoid washing the seed, causing them to
float to the soil surface. Household window sprayers are suitable. Cover
the containers with plastic sheets or panes of glass and place in a cool
room (60 to 65 degrees) away from direct sunlight until germination.
When seeds germinate, move them gradually (over two or three days) into
brighter light. When the seedlings have developed the first true leaves
(the leaves above the cotyledons or “seed leaves”), thin to
one plant per container if using partitioned trays or peat pots. Use tweezers
to pinch off unwanted seedlings rather than pulling them, to avoid disturbing
the remaining seedling.
If seeds were planted in larger containers, transplant into individual
peat pots or other small containers. An alternative is to thin the seedlings
so they are spread about 1 1/2 to 2 inches apart and leave them in the
larger containers. This method, however, makes inefficient use of seed
and space.
Water seedlings carefully. Small containers used for starting plants
dry out quickly. On the other hand, soil kept soaking wet inhibits seedling
growth and may kill the plants.
About one week prior to planting-out time, gradually expose seedlings
to longer periods outdoors unless temperatures are below 50 degrees. At
the same time, reduce watering to a minimum as long as plants do not wilt.
This will help the plants adjust to full exposure without undergoing undue
shock at planting time.
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