Maggie talked with Richard Thompson from Isle,MN this week on her local food segment. Richard grows peaches, pears, apricots and other things you don't necessarily think of as Minnesota Grown products. You can hear the conversation here.
We got great response to this, including Joel, a farm educator and retired market farmer from Mahtowa had some great advice for growers:
Hi Maggie-
Thanks for mentioning the kale query this morning.
Best date to start your tomato plants depends on a number of factors: date when you plan (or feel is safe) to set out, germination and early growing conditions, available light and temperature during "adolescent" seedling growth, length of day and sun angle once you start using natural light conditions for seedling growth, and growing medium fertility.
Best approach is to count backwards from your transplant date. Under ideal conditions, a tomato seedling only needs 8-9 weeks to attain a nice stocky profile with a strong root system. Given a transplant date of June 5, this would mean starting the seedlings around April 1. On this schedule, by the time you pot the seedlings up and get them into natural light (hopefully), it will be mid to late April and day length and sunlight will be quite favorable for rapid growth of stocky seedlings. This is the simplest way to approach the question.
Once you start pushing further back toward winter, a number of factors complicate the issue. I find that when I start tomato plants in early March, I don't usually have seedlings ready to transplant until mid to late May. That's because the light conditions are not as good and temperatures are lower. Of course, you probably don't want to transplant any earlier than mid-May unless your greenhouse is reliably heated.
I start my plants in one of two ways, depending on conditions: 1) in the basement in a germination chamber which has about 15-20 gallons of water with an aquarium heater. Four 11 x 22 flats can fit on lath set over this water which I try to maintain at 75-80F for nightshade germination. Two shop-lite fixtures with one cool and one warm flourescent in each provides close to full spectrum light. As long as the growing tips are kept within 6-10" of the lights, the plants don't get too leggy. Another factor that causes leggy plants is consistently warm growing conditions. A more natural day/night variation of at least 15 degrees F seems to promote a healthier growth. In general, I try to get my seedlings in natural light with more diurnal temperature variation as soon as possible.
Or 2) If weather is warm and wood furnace is not being used regularly (we also have a cookstove in kitchen which provides shoulder season heat), basement gets cold and it gets difficult to keep the germinator warm enough for good results with nightshades, even when the water is 80F. Possibly better insulation of the chamber would be the answer. Anyway, under these conditions I use our propane oven. Pilot light keeps the oven at a nearly ideal temperature for nightshade germination. A couple of downsides to this method--we have cooked more than one flat over the years and you need to monitor the flats quite closely and get them into light as soon as seeds start to germ.
I have two large south-facing windows with a 30 degree angle that is just about right for direct sunlight in February-April. I can fit four 11 x22 flats on the ledges of each of these. Diurnal temperature variation is more than adequate (On below 0 nights I need to protect the plants from freezing).
I try to move the seedlings out to the greenhouse (only heated as necessary) sometime in early May. No point in rushing them into the ground, because soil in an unheated greenhouse takes quite a while to warm up after it thaws out and I like to plant my seedlings deep. Also, if the weather gets too cold to protect them with my somewhat meager heating sytem (propane wall heater) I can always bring the flats into the house. Once the plants are set in the ground, it's a commitment!
With the above method, I never need to worry about hardening off my plants. Research shows that tomato seedlings exposed to 50 degree or lower temperatures during "adolescence" are more productive, so the cool nights are a positive which counterbalances the slowing of growth due to lower average temperatures.
Even if light and temperature conditions are ideal, seedling growth will not be satisfactory unless the growing meduim is fertile. While seeds need virtually nothing to germinate, once they've been potted up in a growing medium, they like plenty of nitrogen for the green growth, and adequate levels of phosphorous, potassium, and micronutrients are also important. I use 2" soil blocks made with peat, compost, good garden soil, vermiculite, wood ashes, and lime. I try to use wood ashes that include powdered bones from remains of chicken, turkey, venision etc. we've cooked or processed. Alternatively, you could use bone meal. Generally get pretty good results with this mix. When seedlings get to 1/2" in diameter, they should be potted up again to something like a 4" pot (I don't have a 4" blockmaker--they're fairly expensive). Once they're in 4" pots, they are not as easy to bring into the house if a cold night threatens them, although I don't have nearly as many plants to manage now so it's not that big an issue.
Setting out plants in the (mostly) unheated greenhouse soil on May 20, I generally expect the first short season hybrids to ripen around Aug 1 and heirlooms to start mid to late August. The real benefit comes from the quantity and quality that come in September when outdoor tomatoes are either blasted by frost or of dubious quality due to the consistently cool nights. I can usually keep a greenhouse producing fairly good quality fruit through mid October, possibly providing one or two nights of supplementary heat. After mid October, the declining day length and more frequent need for supplementary heat make continuing to keep things going a questionable effort.
I don't have much luck with setting slicing tomatoes outdoors here, but normally set out some Sun Gold Cherry tomatoes with tomatillos and husk cherries. Our average last frost date here is June 4, so I usually monitor weather carefully the first 10 days of June and set out in a warm period. Setting plants out on a pre-determined date can be a big mistake if the first 2 nights they are stressed by near-freezing temperatures and cold soil. As long as plants are still happy in their pots, better to wait a little longer.
Basil plants grow much more quickly and are also much more sensitive to cold. Germinating in a warm medium and potting up after a week to 10 days, they can be ready for transplant in 3-4 weeks and will be ready for harvest 2-3 weeks after transplant. This assumes they are not stressed by cold. Even a touch of frost will kill nearly all your plants completely, and the cold soils frequently encountered in the 1st half of June may set them back so much they never do well. When I transplanted basil outdoors, I used to aim for a warm window in late June-early July. Once I started planting them in a greenhouse, I found that early June was about the right time for transplant. Just for some perspective on the importance of warmth for basil. I used to set out 300 plants in a greenhouse and got 100 to 150 lbs good quality leaf with minimal stem annually. I estimate I would have needed 2000 or more plants set outdoors to get this kind of production in our climate (although I never set out more than 700). And even then, the quality would not be nearly as good.
Hope this is helpful.
Joel
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