Hi Jennifer-
I don't get into vernal equinox...too technical for me, but marigolds & petunias can be started now using the Winter Sowing method. Check out the forum!

Here is a link that might be useful: Wintersowing

Vernal Equinox just tends to be another day on the calendar with little or no bearing on local weather conditions for the start of the growing season. Spring or not, we'll be getting snow into early April here.

Never tried it myself, but winter sowing seems to be one of the best ways to get the season started. Otherwise, if you simply want to start some seeds indoors under grow lights or in a sunny window, check your seed packets for basic information on that. If you want to direct sow outdoors, check the last average frost dates for your zone and wait until the soil is workable and warmed up some.

You need to learn your area's average last frost date. Plant your annuals shortly thereafter. If you want to start flowers inside from seed, count backwards eight weeks from your last frost date and sow your seeds then. You must have incredibly sunny windows or a flourescent light set up to do that successfully. Marigolds can be sown right into the ground (after the last frost date) and will rapidly catch up with those started in pots. Petunias (in my SOUTHERN experience) can be sowed outside somewhat before the last frost date and they will come up and do their own thing. But, of course, our late frosts and your late frosts can be entirely different. The Vernal Equinox is honestly just another day on the calendar. What counts is your CLIMATE, when it comes to gardening.

Hi, Jennifer.

I think the vernal equinox is a date of interest, in that I notice that plants respond enthusiastically and quickly become more robust when duration of the dark period becomes less than light duration. Though the equinox has little noticeable bearing on local weather, it certainly has a major impact on plant response. Much, if not most of plant responses are controlled by rhythms (search Circadian and/or endogenous rhythm and add the word 'plant') based on length of photo-period, with the strongest responses concentrated around the vernal equinox & summer solstice. Most plants markedly slow growth extension and foliage production at the summer solstice & begin storing photosynthate for the winter rest. This is a major effect of changing photoperiod, so it's logical to believe that the transition from days shorter than nights to days longer .... has substantial impact on plant physiology as well. Obviously, temperature is able to trump this response, but under favorable temps, the response is very evident.

I always use soil temperatures as the guide to when I should put bedding plants in the ground. Seeds are pretty much self-regulating, but if we put sets out before 3-4" soil temps are above 55*, we invite all kinds of cold-induced nutritional deficiencies, drought responses, physiological disorders, and diseases (many fungal) associated with chilled soil. In many cases, chill injury can be very long lasting & the effects lingering well into the summer, or permanent.

I can't speak for other zones warmer than 6, but in USDA 4,5, and 6, the danger of frost is past when soil temps climb to above 55*, and using soil temps is a very dependable guide.

Al

Well, some stores are selling marigolds and petunias in zone 6 right now and it sort of seemed odd for these hot-weather-loving plants to be on racks right now. Technically, it may be spring but the soil and air temps still say winter.'
If you are planting grown plants, then wait until May. You can sow your seeds indoors now if you have a good light source.