KPOV – The Point
Gardening: Get Good At It
The Astonishing Promise of a Greenhouse
March 24, 2015
On an earlier program we discussed purchasing or building a greenhouse. You’ve done it and now
you’re ready to start those seeds. Let’s go over your start-up check list.
1. First, other than the sun, what is the heat source for your seeds?
For a hobby greenhouse, I would suggest either heating mats (which can be quite expensive)
or heating cables, which is what I use. These cables are most commonly used to melt snow
and ice from the roof edge and gutter on buildings. I actually place them on the surface of my
wooden workbench, stapled with electrical staples, and place a tray of 4 inch pots on top. It
provides just the right amount of heat underneath my seed starts. The cables are connected
to a thermostat so I can keep the seeds warm during the night and eliminate heat on a sunny
day. Seeds of most plants started indoors germinate sooner and produce healthier roots when
the potting mix is warm. Bottom heat can help to prevent “damping off,” which is the death of
tiny seedlings due to pathogens at the surface of the potting mix. Check our website for more
details and photos.
2. Did you know that vegetables and flowering plants require a minimum of 8 hours of light for
maximum growth? Because I only use my greenhouse during early spring for starting seeds, I
have not invested in grow lights. I do have several 4-foot “cool white” fluorescent tubes that
can be raised and lowered to add light if my plants are developing elongated skinny stems.
Don’t leave the lights on continuously. Many plants need some dark period each night to
develop properly. A simple timer can be part of the set-up. If you’ve taken great care in placing
your greenhouse in the best sunny, south facing location, well away from shade, your plants
should get adequate sunlight for seasonal use.
3. A planting schedule is essential. It may seem time consuming but worth the effort instead of
guessing when seeds should be started. If you are new to Central Oregon, you may think that
everything should be planted out the end of May but the soil temperature here is still just too
cold for many plants. I set a date that I estimate to be the last frost date (which is usually the
second week in June). Now, look on the seed packet to find out how many weeks it takes for
that particular seed to mature. Many successful Central Oregon gardeners add an additional
14 days to ensure mature fruits and vegetables. A seed starting chart is available on our
website.
4. Wither you use 4 inch pots or trays or plugs, using soil taken straight from the garden is not
suitable. It may contain pests and weeds and it is not the best soil structure for starting seeds.
Purchase sterile soilless mix or you can make your own. You can use peat pots that are
biodegradable and go directly into the ground or peat pellets that are compressed until you add
water. I use a soilless mix topped with seedling mix in 4 inch pots to cut down on
transplanting. Do your homework and see what works best for you.
5. Keeping the potting mix moist while the seeds are germinating is essential. I use a ‘gentle’
spray setting on a watering wand. You can use a spray bottle or water can be added to a
bottom tray and allowed to move up into the mix.
6. Seedlings draw energy for germination from nutrients stored in the seed. They don’t need
fertilizer until they have several sets of true leaves.
That should get you started. Until the final installment in the greenhouse series, visit our website:
gocomga.com and click on the KPOV tab on the orange bar for answers to all your garden
questions. This has been Gardening: Get Good At It. Thanks for listening.
Recommended Reading:
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Greenhouse Gardener’s Companion by Shane Smith
How to Build Your Own Greenhouse by Roger Marshall
Publications from our website include: Seed Starting Schedule; Central Oregon Vegetable Garden
Calendar; Recommended Vegetables for Central Oregon
IN MY GREENHOUSE, HEATING CABLES
ARE PLACED ON A WOODEN BENCH AND
HELD IN PLACE WITH ELECTRICAL
STAPLES. TIMER IS USED TO CONTROL
HOURS OF OPERATION. DAYTIME HEAT
IS USUALLY SUFFICIENT FOR
GERMNATION WHEN FULL SUN IS
AVAILABLE AND GREENHOUSE
LOCATION IS APPROPRIATE.