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How to determine your own personalized last frost date from local weather station

There was a discussion in comments on my previous average last frost post on how to determine an accurate last frost.  A great point was made by Daphne where every garden can have its own microclimate so the date you find online or in a book could be many weeks off for your microclimate in neighborhood.

To be able to predict your last frost date accurately it takes some history, if you have lived in your current residence and happened been capturing your temperature data accurately by memory or paper you may the information to predict your last frost date.

For people that are relatively new to their residence, like myself, I felt there I had very little information to determine an accurate prediction of my last frost date.  This was until I remembered Weather Underground which logs results of schools or private individual that register their weather stations.

After a quick search I was able to find someone who had a weather station in my neighborhood.  After doing a custom query of the full range of the of the weather station, which in my case was a little over 4 years, I had all the information I needed.  By carefully adding a horizontal line at freezing using a graphics program (Microsoft Paint) I could easily see where the low temperature dipped below the freezing mark.

tempChart

From a quick glance at the data it appears that the first week of April is a pretty safe date for past few years.  But if you look the the irregular low temperatures we have had this month this might be harder than I thought.

Now of course your neighbor may a different microclimate than you, but should get you in a better ballpark than the generic number you find fro your city.  You could always spend $500-$1000 on your own weather station to get some better accuracy, but for me seems close enough to me.  Though the weather station would be a really cool gadget to have.

Last frost dates are not the same

It came to my attention it seemed every time I see my average last frost date it comes up as a different date.

Average Frost Date (Seattle, WA) Location
3/10 The Old Farmer’s Almanac
4/20 Victory Seed Company
3/22 Ed Hume’s Seeds
4/15 USDA Zones
5/14 USA Gardener
3/25 Clyde’s Garden Planner
3/24 Garden Web

 

 

 

 

 

 

 

Now the humorous part of this is I didn’t go out trying to find as many non-matching dates as I could, these came in order from my Google query for “last frost dates”.

Under conventional wisdom, this number should be simply an average of the last frost dates for the past 30-40 years to give you about a 50% chance of avoiding frost given past history.  So it seems really strange why these numbers vary so much.

Then I came across U.S. Climate Normals this site includes no only the dates but the probability of them being true.  So if you are a betting man/woman (or just impatient) you can press your luck and plant with variable odds.

For my area (Seattle, WA) I have the following options:

Probability Level
Threshold (°F) 90% 50% 10%
36 °F Mar 27 Apr 11 May 18
32 °F Feb 13 Mar 10 Apr 22
28 °F Jan 01 Feb 25 Mar 20
From the information above, only The Farmer’s Almanac had the number I was really expecting.  But given the information above and how late frosts have “bitten” me in the past I think I will give myself a couple extra weeks and plan on my last frost being Mar 24th to hopefully avoid and hard frosts for tender seedlings.

Average last frost dates are only right half of the time

Our last frost date in my area should have been March 24th but given the frosty mornings this past week and the fact we had snow coming down most of today it looks like this year our last frost date will fall on the other side of the bell curve. Unfortunately, I was optimistic with some of the great weather we were having earlier and planted my tomato seeds for a much earlier move outside. The poor tomatoes are still growing in my PC grow box but starting to not look so good. As you can see from the picture below my tomato plants are in some dire need of some non-artificial light. I am afraid I might end up buying my tomato plants at my local nursery (yet again) this year. Vegetable gardening is definitely one of those hobbies which it does not pay to be a too optimistic.

When to start garden seeds indoors: Seed starting calculator

When to start your vegetable seeds

When you start seeds indoors in a vegetable garden, it can be difficult getting your schedule down to ensure that start your vegetable seeds with enough lead time that they are mature enough to venture outside but also not so large they take over your growing area.

Personally this has been a difficult part for me where I am really good getting the early vegetables started on time (onions, peppers, tomatoes) but when it comes to the later plants and/or second/third plantings is where I begin to get forgetful.  Over the years I have come across a couple of great tools to make this easier that I thought I would share.

No matter which option you choose to start garden seeds indoors you will need to determine an important date, your last frost date. There are many sites/tables out there that will give an estimate I actually have a couple posts on the subject but at the moment my favorite site that makes this very easy is WeatherSpark, it uses historical data with great visuals to easily determine when the best probability of picking the right date. Here you can take a look at this historical data and make your call of what date you think will be safe.

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1. Create a garden schedule.  Just by figuring out your last frost date and doing a little math (Excel works great for this) you can determine the optimal seed starting dates and even get a general idea of when your plants should be ready for transplanting.  What I love about this technique is you can tweak it each year as things worked well (or not so well) in previous years to get the schedule finely tuned to your particular garden and the micro-climates within it.

In addition knowing an estimate of when these plants will be venturing out in the wild can assist in your space planning for your seeding area as well as having a reality check if you see your peppers will be ready to be transplanted in March when it doesn’t get above freezing until mid-June.

Here is my schedule for starting seeds indoors my area and estimated last frost date (April 20th), though sure everyone that is reading this will not have the same date as mine so thanks to my infinite nerdiness I made the following table so you can adjust the “Last Frost Date” to yours and see how my schedule would look in your area.

 Last Frost Date:  
Vegetable Name Seed Start Date Estimated
Transplant
Date
Estimated
Harvest
Date
Celery 1/19/2013 3/18/2013 4/24/2013
Onion 1/19/2013 3/25/2013 5/24/2013
Leeks 1/19/2013 3/21/2013 6/3/2013
Kale 1/26/2013 3/7/2013 3/22/2013
Artichoke 1/31/2013 4/27/2013 6/20/2013
Kohlrabi 2/9/2013 3/15/2013 4/5/2013
Pak Choi 2/9/2013 3/6/2013 4/10/2013
Parsley 2/8/2013 4/6/2013 4/24/2013
Lettuce 2/9/2013 3/6/2013 4/5/2013
Broccoli 2/9/2013 3/15/2013 4/20/2013
Pepper – Jalapeno 2/9/2013 4/28/2013 4/25/2013
Pepper – Bell 2/9/2013 5/4/2013 4/25/2013
Swiss Chard 2/16/2013 3/20/2013 4/7/2013
Cabbage 2/16/2013 3/31/2013 5/7/2013
Brussel Sprouts 2/22/2013 3/31/2013 5/23/2013
Collards 3/2/2013 3/24/2013 5/1/2013
Tomato 3/2/2013 5/4/2013 5/21/2013
Spinach 3/9/2013 4/23/2013
Peas 3/9/2013 5/13/2013
Turnips 3/9/2013 5/8/2013
Watermelon 3/16/2013 5/27/2013 6/14/2013
Basil 3/24/2013 5/14/2013 6/22/2013
Potatoes 3/30/2013 7/8/2013
Radish 3/31/2013 5/5/2013
Beets 3/31/2013 6/4/2013
Carrots 4/9/2013 6/23/2013
Corn 4/9/2013 5/7/2013 6/28/2013
Cucumber 4/9/2013 5/16/2013 6/8/2013
Okra 4/9/2013 5/11/2013 6/13/2013
Pumpkin 4/9/2013 5/7/2013 7/28/2013
Summer Squash – Sunburst 4/9/2013 5/16/2013 6/3/2013
Winter Squash – Hunter 4/9/2013 5/16/2013 7/3/2013
Zucchini 4/9/2013 5/16/2013 6/3/2013
Lettuce 4/13/2013 6/7/2013
Beans 5/4/2013 7/13/2013
Dill 5/11/2013 7/15/2013
Carrots 5/27/2013 8/10/2013
Broccoli 6/22/2013 8/2/2013 8/31/2013
Cabbage 6/22/2013 8/2/2013 9/10/2013
Kale 6/22/2013 7/22/2013 8/16/2013
Kohlrabi 6/22/2013 7/29/2013 8/16/2013
Cabbage – Napa 7/24/2013 8/21/2013 10/7/2013
Pak Choi 7/24/2013 8/21/2013 9/22/2013
Onion – Bunching 7/24/2013 10/2/2013
Turnip 7/24/2013 9/22/2013
Lettuce 8/3/2013 9/27/2013
Spinach 8/10/2013 9/24/2013
Corn Salad 8/10/2013 9/29/2013
Garlic 10/12/2013 2/14/2014
Pak Choi 12/14/2013 1/26/2014 2/12/2014

* N/A because vegetables should be sown directly in the ground.

 

2. Create a garden plan online and get reminders.  My favorite online vegetable gardening software is GrowVeg.  It is very easy to use and provides some great visuals when to specifically plant seeds and transplant your seedlings outdoors, which you can see below.

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In addition you also can recreate a virtual copy of your garden and plan exactly where you want to plant your vegetables, to ensure your ambitions for growing a huge crop this year does not exceed the reality of the limited space you have to actually grow.  It also remembers where you planted vegetables in previous years to help enforce crop rotation to ensure pests/diseases will be forced to remain in check.

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Though one of my favorite features is the weekly reminders, once a week you get a simple email letting you know what plants you should be starting/transplanting that week.  This was very helpful later in the season where I probably would have completely forgotten about my carrots without this helpful reminder.

 

3. Buy a garden planning book.  If you want something that you can really get your hands on you might want to check out the Week-by-Week Vegetable Gardener’s Handbook helps with this problem by providing weekly reminders of what vegetables you should be order/planting and what preparations you should be doing in your garden.  This can be a very helpful tool in getting a little more organized in your vegetable garden.

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Already falling behind on your seed planting here are a few great options to get a great selection of seeds without spending a lot of money:

  • One of my favorites is Burpee Seeds, they have been around since 1876 and definitely know their stuff. The actually have a seed sale going on now where you get $15 off on order of $75 (just use code AFFB4A35) expires on 1/15.
  • The name is not too exciting but Generic Seeds offers no thrills packaging with quality seeds and very reasonable prices and if you spend $20 or more shipping is on them.

When to bring your vegetables outside?

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Every time I have a discussion with a beginner gardener, this is the most common question.  Typically the answer involves figuring out your last frost date then doing some backwards math when to start your seeds or purchase your plants from your local nursery.  The problem with this is there is an assumption of the rate at which temperatures will increase after this no frost date.  It doesn’t really matter how many weeks after the last frost when you bring out your tomatoes but the fact that it is over 65° F

Read More …

How to make your own cheap weather station

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Though the prices for personal weather station have dramatically dropped (around $100) over the past few years, I decided to work on making my own. The primary measurement I wanted was temperature given this is the specific one that could be dramatically different from my neighbors (or neighborhood weather station) given the many unique microclimates your yard can have.

Step 1: Create an account and weather station at Weather Underground. This will allow you a place to view your weather station results as well as a permanent storage location for your data. After you have created your account it is really easy to create a weather station after clicking this link you just need to enter some basic information such as address and time zone click “Submit” and you have yourself a weather station. Now this is not very exciting unless data is being updated so we will look at this next.

Read More …

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