When Should I Plant My Veggie Seeds?

The question I have been asked over and over again this past week is, “Stacy, when should I plant my vegetable seeds?”   Okay, let me start off by saying that this is a loaded question.  There are so many possible answers, truths, and additional questions that my head starts to spin.  I certainly can’t do this complex question justice in a text, or Facebook post.  So, I am turning to my blog to give my long winded answer to this question.

There are many ways to determine your planting dates and they include; calculation of the last and first freeze date, finding your USDA planting zone, determining the soil’s temperature, reading The Old Farmer’s Almanac, studying phenology, and even charting the moon’s phases.   Some may sound more scientific than others, but I think they all have valid points to make.  Which is why I suggest you use information from a combination of these resources to find the ideal planting dates for YOUR garden.

Let’s begin by using your area’s last freeze date.  The Accuracy Project.org has 3 handy maps to help you determine your garden’s growing season.  Their maps include the last average freeze date, the first average freeze date, and the average length of the growing season.  The map below shows the average last freeze date for each region, however, the actual last freeze date often varies widely year to year.

Mother Nature is fickle, and it’s not unheard of to experience snow in April, or a late freeze in May, so you are rolling the dice if you decide to plant based on this map alone.  Plus, some plants can tolerate some degree of frost, other’s cannot.  You may get a freak cold snap that kills all those tender bean shoots, but your peas and carrots will survive.  Always consult the back of your seed packet to determine whether a seedling can handle a hard frost, light frost, or no frost at all, when deciding your planting date.

Similar to using the last freeze date, the USDA Plant Hardiness Map, uses the average annual extreme coldest temperature to divide the country into planting ‘zones’.  Like knowing your credit score, or blood type, it’s important to know your USDA Plant Hardiness Zone if you are a gardener.  This map is the go to standard used by most growers, seed companies, nurseries, catalogs, landscapers, and gardeners.

To find your zone, visit the USDA site and type in your zip code.  Once you know your zone, a quick Google search will render you a planting guide for your zone.  Easy peasy, lemon squeezy, you now know when to plant your seeds.  Or, do you?

Here is the main issue I have with this map, the zones are WAY to broad.  According to the map, Seattle, WA is in zone 8, as is Tucson, AZ.  WTF?  I live in Seattle and I have visited Tucson.  I can state without a shadow of a doubt that our climate, precipitation, elevation, landscape, and vegetation are nothing alike.  I highly doubt that lettuce will be planted and harvested on the same dates in these two cities, even though they share a zone.

If you do decide to look up a planting chart based on your zone, make sure you find out where the chart’s author resides.  For example, I like to use the Territorial Seed Company’s planting charts because they are based in Cottage Grove, OR.  Not only are they in zone 8, but The Territorial Seed Company is also in a growing region similar to my own here in the Pacific Northwest.  Using a planting chart written by a zone 8 gardener in Tucson, AZ would not work out well for my veggie garden.

The next thing you need to take into consideration is the soil temperature.  After all, the soil is where those little seeds will be buried, and if the soil is too cold and/or too wet, the seeds will rot and die.  You can find the required soil temperature for germination on the back of most seed packets.  If the seed packet doesn’t tell you, a quick Google search will.

To find data on soil temperature, visit Greencastonline.com, which has an up to date soil temperature map for the entire nation.  It will even give you a more detailed view of your specific region, as well as a 5 day forecast.

If you are really dedicated, grab an espresso thermometer and check your own garden’s temperature first thing in the morning.  I have a garden loving friend who has been doing this.  She has even been kind enough to email me the soil temps once a week.  Love that crazy plant nerd and her dedication to science and gardening!

Up next in our discussion is The Old Farmer’s Almanac.  As American as apple pie, this publication was once thought to be so accurate, that when a German spy was caught with a copy in 1942, The Old Farmer’s Almanac was accused of supplying the enemy with valuable information.  Yikes!

The Old Farmer’s Almanac still uses the same secret weather forecasting formula, devised by Robert Thomas, the original publisher, back in 1792.  Thomas observed natural earth cycles, like tides and weather, to create a complex formula for weather prediction, that the publication claims is 80% accurate.  The secret formula is still locked away in a secret tin box in Dublin, New Hampshire, where the booklet is published.

To find your planting dates, simply plug in your city and state and the USDA site will provide you with a printable, detailed list of planting and harvesting dates.

Nice!  Well, kind of.  Is this publisher actually trying to convince me they can accurately predict the weather a year in advance, when my own local weather guy can’t even give me an accurate forecast for tomorrow night?   Ha!  Don’t make me laugh.  It’s just not possible.  If that was the case, we wouldn’t even need weather forecasters, just a trusty copy of that little guide. Instead, I will take the information they have provided me with and add it to my gardening arsenal.

Time to get really wacky on you, so hold on, because next we are charting the moon’s phases for sowing seeds.  The moon’s gravitational pull has long been believed to greatly affect nature and behavior.  Nursing friends of mine have told me the ER is crazier during a full moon.   My old veterinarian swore dogs acted strangely during a full moon, and even parents have been known to blame their child’s behavior on the light of the full moon.  Well, planting by the moons phases is also believed to effect the growth and development of plants.

Come on!  Really?  Yup, that’s what I have heard.  At my last garden club meeting, a couple of the ladies brought up moon charting, and although they warned us not to believe everything we read, they did admit that after years of personal observation, there are some plants that seem to respond better to moon planting.  Who am I to poo poo centuries of charting and my wise gardening elders?  The Old Farmer’s Almanac even recommends moon planting, as well as using the moon as a guide for other farming related chores, such as fence building and castrating animals.

To learn more about the theory behind moon phase planting, check out Gardening By The Moon.  To find the moon planting chart for your region, use this handy tool, found at The Old Farmer’s Almanac.

The last topic of discussion, and my personal favorite, is phenology, the study of the relationships between climate and periodic biological phenomena.  These phenomena include things like plants flowering, insects hatching, and birds migrating.  Studying phenology can teach gardeners to recognize certain indicators in nature.  These indicators can then help them determine when its a good time to plant certain crops or, when to be on the look out for specific pests.  The weather and frost dates may be different each year, but watching nature’s cues can guide you in the right direction because many plants and animals respond to certain temperature and seasonal changes.

A few of my favorite phenological sayings are:

  • Plant your peas when the forsythia bloom.
  • Plant your potatoes when the first dandelion blooms.
  • Plant cole crops, carrots, and lettuce when the lilac leaf is as big as a mouse ear.
  • Plant your tomatoes when lily of the valley are in bloom.
  • Plant your peppers when the bearded iris blooms.

These are just a few examples of the phenological advice gardeners have been passing on for generations.  For more phenological cues, visit the Golden Harvest Organics website.  The theory may seem simple, but it makes perfect sense to me, and one of the reasons is because of what I have witnessed in my own town over the last 10 years.  Let me explain, as if I haven’t done enough yapping already.

As you probably know, the Seattle area varies greatly in elevation.  Today, I planted my peas because the forsythia bush in my yard is in full bloom.  On the other hand, my friend, who lives just 2 miles away, has a forsythia in her yard that bloomed over a week ago.  Five miiles up the road from me, another gardener I know, won’t be planting her peas for a least another 2 weeks because her forsythia is just beginning to bud.  We are in the same zone, the same city, we are even within a 5 mile radius, and yet our microclimates vary widely.  This is why I like to pay attention to what nature is telling me in my particular garden.

There is even some fascinating research, being done by USA National Phenology Network, on the timing of spring’s arrival in particular areas, and it even takes into consideration the effect of climate change.  By studying the past and current weather conditions and leaf-out times, Extended Spring Indices, which are statistical models, are created to predict the future arrival times of leaf-out across the nation.

It is an interesting read if you enjoy the science behind gardening, and they update the leaf-out map weekly, so it’s worth checking out.

To summarize the lengthy answer I have just given to when you should plant your seeds, here is some of the information to consider:

  • What is your last average frost date?
  • What is your first average frost date?
  • How long is your growing season?
  • What USDA Hardiness Zone are you?
  • What is the soil temperature?
  • What information does the seed packet provide?
  • What weather predictions have been made for your area?
  • What phase is the moon cycle?
  • What phenological indicators is nature giving you?

Ask yourself some of these questions, or all of these questions, visit a few of the websites I suggested, and you will be able to figure out the best time to plant your very own veggie garden.  If that doesn’t work, reach out to a gardener you may know in your area.  We tend to be a friendly bunch of people and typically enjoy sharing gardening advice and stories.   Happy seed starting, gardening friends, and please, do share!   I would love to hear how your growing season is coming along.  Cheers!







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