Greenhouse Seeds Started Indoors

Greenhouse Growing Tips

Great greenhouse tips and useful information to
keep your greenhouse running efficiently.




Seeds Started Indoors

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.

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.

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.


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.

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