Plant a late season garden
iGrow Garden Column for week of June 29
It’s Not Too Late to Plant Vegetables
By Rhoda Burrows, SDSU Extension Horticulture Specialist
With all the rain we have been getting in the Black Hills and some other areas, gardeners here have had a hard time getting their crops in the ground. When confronted with soggy wet soils, one begins to appreciate the strategy of permanent raised beds with walkways in-between! Whether you have struggled with soils too wet to work, or have just fallen behind in your planting, you may be happy to know it is not too late to plant a wide variety of vegetables.
Following are some guidelines for determining the last planting date for different types of vegetables for your area. First, you need to determine your average first fall frost date. If you have kept records in previous years, you probably already know about when to expect that first frost. If not, you can check out this handy interactive website map:http://climate.sdstate.edu/w_info/frost/frost.asp
Note that this website allows you to select both the % probability and the temperature for fall or spring frosts – try putting in different options and observe the effect on the frost date for your area. For cold sensitive crops such as green beans or basil, select the 32 degree option; for crops that are a bit hardier (many can take at least a few hours of 28 to 30 degrees), or if you use row covers, choose the 28 degree option. For my area, there is an average of 10 days difference in frost dates between those two temperature selections. Along with your average first frost date, you need to know the average days to maturity for the different vegetable varieties you would like to grow. This can be found on the seed packet, or in the seed catalog. For example, many summer squash take about 50 days to mature, while winter squash are around 100 days. Now count backwards from your expected frost date the number of day to maturity (there are calculators online that will do this for you if you don’t like thumbing through a calendar – just search for “harvest date calculator.”) This will give you an approximate “plant by” date.
However, you may want to refine this date, taking into account some further considerations: (1) the days to maturity is an estimate of when the crop will first be ready for harvest, but it doesn’t take into account crops that keep producing over a period of time, so you may want to plant earlier so that the crop is producing for a time period before the first expected killing frost; (2) if your fall temperatures are generally cool, crops will mature a week or two more slowly, especially warm season crops such as tomatoes and squash; (3) some crops will be killed by a light frost, while others can survive even into the lower 20’s; and (4) in warm soils, most seeds will germinate more quickly and plants will grow more rapidly than might be expected earlier in the year.
Some examples, using a somewhat conservative expected fall frost date of Sept 24 (adjust the following planting dates accordingly if your frost date differs):
- Beets (50 days) can tolerate high 20’s, so they can be planted through the end of July
- Green beans (55 days) are very frost sensitive, and should be planted by July 17th
- Melons (70 days) are also frost sensitive, and should be planted by July 2nd
- Peas (65 days) - these plants can tolerate frost, but the pods cannot, so plant by mid-July
- Carrots (50 to 65 days) can be left in the ground until a killing frost, or later with heavy mulch; plant by the end of July.
- Sweet corn (75 days) is another warm season crop that won’t grow under 50 degrees, so plant it by early July.
- Radish (30 to 35 days) roots can tolerate down to soil freezing; however, they do not grow well under long-days (15 hrs) and warm temperatures (over 70 degrees), so plant them in August or early September. Or grow longer-season (60 days), more heat tolerant icicle types.
Spinach (35-45 days) is frost tolerant; germination is reduced in soils over 70 degrees, so plant in mid- to late-August; earlier in cooler years. (Or pre-germinate your seed on moist paper towels in your refrigerator.)
For spinach-like greens during the summer, plant New Zealand spinach or Orach, which are heat-tolerant. Keep in mind you can plant later than the above dates if you can provide frost protection, such as row covers. Often you need only a few degrees difference to keep plants growing for another week or two, or sometimes three. We often experience frost for just a couple nights, then the weather warms again so protecting the plants during those few frosty nights can make a big difference in the length of the growing season for your plants.