Seed starting indoors is exciting and infectious, and you'll soon find that
your windowsills are crammed with little pots of seedlings and you have
an overwhelming desire to study greenhouse designs. But a greenhouse is
not necessary for a satisfactory experience in gardening, as long as you
follow some practical considerations such as light and temperature requirements,
and space. A tray of seedlings is only a starting point, as these seedlings
will have to be transplanted on to larger containers as they grow, taking
up more and more room.
For many gardeners, providing suitable warmth can be as
easy as placing the seed tray near the hot water heater or near the home
heat source, on top of the refrigerator, or in a sunny windowsill. If
the packet instructions call for very warm temperatures, or if conditions
in your home are generally unsuitable for even the minimum germination
temperature, commercial propagation mats are available. These mats
provide constant, steady warmth at a thermostatically-controlled setting
and are essential for proper germination of many tropical seeds.
After germination, the general recommendation is to drop
the temperature by 10°F from the optimum germination temperature and
grow seedlings on in a cool, well-ventilated area with a good light source
or under grow lights. Keep out of cold windowsills at night where drafts
could damage seeds and young seedlings.
Most seeds germinate best if the tray is covered with
a sheet of glass or loosely covered with a sheet of plastic wrap to retain
moisture. Light and dark requirements are noted on the seed packet and
should be followed carefully. Seeds that are non-specific in their light
requirement for germination will not have a notation. For seed that require
darkness for germination, check periodically under the darkening cover
for signs of growth. Once the majority of the seedlings are through, remove
the darkening covering and bring into bright but indirect light. Remember
that seedlings under glass or plastic wrap and placed in a hot, sunny
windowsill will literally cook as temperatures can easily reach over 100°F.
When seeds germinate, the first leaves to appear are the
cotyledons or seed leaves. These are usually a pair of oval, fleshy leaves
that bear no resemblance to the mature leaves of the plant.
The conventional advice is that seedlings should not be
pricked out or transplanted until the first true leaves appear. In the
case of large seedlings such as cucumbers or squash however, plants are
large enough to handle before the rue leaves develop. It is sound advice
to plant these large seeds in individual containers and eliminate the
need for transplanting.
Remove tiny seedlings from the sowing container into individual
pots of potting soil can be a delicate business. As seedling stems are
easily bruised, always handle seedlings by their seed leaves. To facilitate
removal of the seedlings, use a tapered stick, a narrow flat-ended screwdriver,
or a metal device called a widger to separate and ease out the seedlings,
taking care not to damage the delicate roots. Where several seedlings
are growing in a very small space, it is best to transplant a clump of
seedlings and then snip off all but one or two. If seedlings seem sturdy
enough, you can gently tease 2 or 3 seedlings apart, but any damage to
the root system will make survival risky.
Prior to transplanting, fill the clean new pots with pre-moistened
potting soil. Using the end of a pencil, make a small hole in the center
of each pot to accommodate the transplant. After easing the seedling out
of the sowing tray, move directly into the new pot and firm potting soil
around the delicate root system while still holding onto the seed leaf.
Water immediately with a gentle spray of lukewarm water. Set the pots
out of direct sun and protect from wind for several days. It is not advisable
to use a fertilizer at the time of transplanting as feeder roots are invariably
torn and more likely to be damaged by fertilizer salts. After about 2
weeks, commence fertilization with diluted (1/4 strength) liquid fertilizers.
Invariably, there will be more seedlings to transplant
than pots to accommodate them. As a very rough guide, figure on 50 transplants
produced from a full size nursery flat.
Seedlings such as half-hardy annuals, half-hardy perennials
and many vegetables that are started indoors with heat must be gradually
acclimated to the stronger light, winds and generally cooler night temperatures
of the outdoors prior to planting out in their final locations. This conditioning
is known as "hardening off" and traditionally takes from 7 to
10 days. The correct timing of plants for both hardening off and final
site planting depends on the plant's genetic cold hardiness and climate
factors for your particular area.
When seedlings have reached an appropriate size and the
time is right for the individual plants to go outdoors in their final
location, start the process of hardening off by placing pots or flats
outdoors for several hours a day in a location with some morning sun and
protection from winds. Return to the protection of an unheated porch,
garage or greenhouse for the late afternoon and evening hours. Slowly
increase the amount of time plants are left outdoors and increase the
light they receive to the appropriate light levels over a period of 1
to 2 weeks, eventually leaving plants outdoors all night. At the end of
this period, plants are fully ready to go into the garden.
Remember to protect plants from predicted hard frosts,
freezing winds and heavy rains, which can dislodge seedlings. A useful
aid in both growing cold-hardy seedlings and hardening off tender plants
is a cold frame. A cold frame is an unheated 4-walled structure
with a glass or plastic roof. Materials can be as inexpensive as discarded
lumber and an old window sash. During the day, the glass or plastic top
should be raised for air circulation, but at night it is lowered to protect
seedlings from frost and freezing winds.