Getting a head start on your spring garden at home can be a lot of fun if it turns out right or perhaps a bit disappointing if it flops. Timing your head start right will make a big difference. In this column, I'll take a look at how I go about my spring seeding plans for the greenhouse and what lessons you can take home with you.
To preface this introduction, I'll tell you that I’ve 20 years experience as a professional greenhouse grower. The technology available in this industry today mirrors anything you can imagine from a space shuttle launch to an automated car manufacturing plant. A friend of mine grows peppers at a greenhouse with the roof vent movements triangulated to three different airports’ weather sensors and accompanying satellites. The vents open and close based on the future cloud movements predicted ahead of time. Most of the poinsettias in the stores this year come out of a greenhouse that uses the latest in automation moving cuttings through robotic transplanting to placement of individual pots on the heated floor of a greenhouse for finishing. These greenhouses are very capital-intensive operations. Mine is not so much so. But then the local weather forecasts lack a little something as well.
Step one is to purchase good quality garden seeds. Pick strong growing varieties that have immunity to common disease problems. Good seed companies tell you this kind of information up front. Use clean and sterile containers with some form of drainage, and I recommend a sterile potting soil with finer particles for good seed to soil contact. A rule of thumb is to plant seeds no more than twice as deep as the seed is big. Seeds need consistent moisture once they start to germinate but too much water will drown them. Some seeds require light to germinate but most don’t. I use a thin covering of vermiculite in the greenhouse for seeds that require darkness.
Next to correct soil moisture, soil temperature is your next most critical factor. Get the temperature and moisture levels just right and you will be really surprised at how well you seedlings grow. In my greenhouse, on the germination table I use a soil heating cable set to 27 to 30 C sitting on a slab of concrete backer board, the kind you would find used behind a bathroom shower wall. It helps to disperse the heat. Clean sand would work, too. It’s nice and warm to the touch. The seeds do not need supplemental light at this time, so if it's a choice between sitting your tray on top of a warm but dark appliance or the windowsill, go for the warmth.
When do you know the correct time to start? Commercially, we measure the growing season off by the week from the start of the year. I take the date I want the crop to be ready for and work backwards. Let's say the last frost is usually on the May long weekend. We'll call that week 21. We are now at week 9. Most good seed takes one week to 10 days to germinate at the extra warm temperature. Once germination is complete, we cool them down a few degrees to prevent stretching and provide additional light.
Our big problem here in the valley is that we get socked in by cloud. It keeps our outdoor temperatures warmer, but for plants to really grow they need sunshine. I'll use tomato as an example: 24 C minimum, cover with vermiculite (or your seedling mix), one week to germinate, two weeks to grow some roots before transplanting and eight weeks grown fairly cool at just below normal room temperature.
So working back from week 21, you could estimate that it will take you 11 weeks to get them ready for the garden. Start them next week for good results.
Peppers could use a little more heat to germinate. In addition, they will probably require an extra week of time in between germination and the first transplanting. Normally, I would say to plant them a week earlier than tomatoes but because they really won't like being transplanted outside into the cold soil you could start them in week 11 and leave them inside until the soil warms up a bit more.
I guess the main point is to consider that this isn't going to be an early spring. If you need to feed your seedlings try about a half-gram of 20-20-20 per liter of warm water. Graduate them to a full gram once they have a set of true leaves, not the ones that popped out of the seed.
Two things you can try to keep your plants shorter are to brush them gently with your hand in the morning or give them a shock of cool air for a little bit every morning. It is in the morning that their cells divide, and if you can temporarily impair their growth at that time they will stay shorter.
In general, I find that most seedlings started a bit later grow faster due to the extra sun and warmth. Grow your cool loving crops first and wait for the heat loving crops. Longer days and brighter sunshine will help.
Evan and Wendy Davies own Beltane Nursery at 2915 Highway 3 in Erickson.