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This page:Climate and timing | Degree Days | Wind, Light, Shade | Ultraviolet

Climate and timing

Growing Season

That time, between the last frost of Spring and the first frost of Fall, is the growing season. Obviously many cold-hardy plants will grow before and after this period. The 'season' can even be extended on either end by covering plants in clear plastic tents. But most varieties we really like to grow will only do marginally better in tents, and tents for many are impractical. So we are stuck with the season that Nature has given us.

What most garden books do not talk about is the phenomena of night growth. I believe that most plant growth occurs at night. We in Wyoming have adequate day temperatures to plant many varieties that should do well here but do not. I think that happens because our nights begin to cool in late July. By late August cool nights are the norm. This limits plant growth and there is not much we can do about that. There are only 100 days between May 25 and September 3, and about half of those will have cool nights. This means we have a season with only about 50 warm nights. That makes a big difference.

You must resign yourself to the idea that you will have to choose varieties that do not require as many days to maturity as other varieties. The search for short season varieties will be a life-long process, I promise. The real trick is not just getting varieties to grow, but to get them to produce abundantly. I have created pages on this site to help in the search for good short season varieties, with recommendations to get you started.

Spring, Summer, and Fall Crops

Other parts of the U.S. have distinct seasons that are long in duration. The old joke here in Wyoming is that we do have Spring, but no one can predict which day that will be. It is simply foolish, with our short growing season, to think in terms of Spring, Summer, or Fall crops. I know that many books you read will talk of these. But our growing season is so short that, with a few exceptions, we just get one growing season.

LADF Planting vs Soil Temperature

Here in Wyoming the last average day of frost (LADF) is in late May. In Casper it is May 25. We often get a frost between September 3 and September 10. If plants are covered during the traditional 'garden wrecker' September cold spell, they can usually produce for another two weeks or more. This year (2001) we extended the season into October. We had a cold Spring but a warm, mild Fall.

Many books and seed packets will tell you when, in relation to the LADF, to start plants, when to set them out, and when to direct-sow them into your garden. I have followed this advise for many years, but am beginning to doubt the wisdom of doing so.

This last Spring (2001) saw me replanting beans, lettuce, radish, and carrots, even though I had originally planted them late according to the advise of books and seed packets. The second plantings did just fine, and I think I know why: SOIL TEMPERATURE.

I think seeds germinated well for me after the second planting because the soil had finally warmed to an adequate temperature. Next season I will plant only when soil temperature is high enough to get good seed germination. That means I may plant as early as April or as late as June. I am betting that soil temperature is a much more critical factor than the LADF.

Here is a chart to use as a rough guide for soil temperature planting:

Percentage of seed germination per soil warmth

(temperature in farenheit scale)

Crop 41 degrees 50 degrees 59 degrees 68 degrees 77 degrees
Beans 0 1 97 90 97
Beets 114 156 189 193 209
Cabbage 27 78 93 * 99
Carrots 48 93 95 96 96
Corn 0 47 97 97 98
Cucumber 0 0 95 99 99
Eggplant * * * 21 53
Lettuce 98 98 99 99 99
Musk Melon * * * 38 94
Onion 98 98 98 99 97
Parsley * 63 * 69 64
Peas 89 94 93 93 94
Peppers 0 1 70 96 98
Radishes 42 76 97 95 97
Spinach 96 91 82 52 28
Tomatoes 0 82 98 98 97

A problem of timing:

I usually plant my lettuce early, weeks before the LADF. This last Spring (2001) I did not. I planted over a full week past the LADF, and still I got lousy germination. My second planting of lettuce did just fine. In fact none of my lettuce bolted all summer, despite the fact that we had a good hot summer. I do plant bolt-resistant varieties, and that helps. But I believe my success this year was due simply to the fact that I planted my main crop of lettuce so late. Lettuce probably bolts after a certain amount of time in the ground, and it just did not get enough time to do that before it encountered cool nights, which may inhibit the bolting of lettuce. It is just a matter of timing.

Here is a proposal. Try some early plantings of lettuce, radish, and spinach in April. You may have to build a tent to cover your bed to boost soil temperatures to achieve germination. Then plan on picking the radishes in May and June. Pick all the lettuce and spinach by July 1. Then on July 1, plant a good short season bean (Top Crop or Contender) in that space. This is succession planting (one crop after another) and it may be the only one that will work here in Wyoming.

Meanwhile, set aside a bed or two for your main crop of lettuces. Sorry, but late spinach plantings tend not to germinate. So don't bother with late spinach. See chart above. Do not plant your main crop lettuce until June 10 or later. I think you will be quite happy with the results from this late planting.

Degree Days: the 2002 temperatures:

Below is are charts that show the daily highs and lows for the 2002 gardening season in Casper, Wyoming. Please note that the Last Average Day of Frost in Casper is May 25, and that we hit it exactly. Please also note that most plants don't actually grow until evening teperatures rise above 50 degrees Farenheit. What the charts show is that from June 9 through June 15 we underwent a cold spell. Evening temperatures did not rise above 50 degrees until June 21. We did most of our reseeding around June 26. The first hard frost was September 22.

Degree Days are the number of average temperature degrees above 50 degrees each day, and they add as the season progresses. For instance, May 26 had an average temperature of 60 degrees, so that day's degrees are 10 (60-50=10). May 27 had an average temperature of 60.5 degrees. Its ten degrees are added to the previous total (10) to arrive at 20 degrees. I have given a starting point of May 26, the day after the last average day of frost.

DAY May
24
25
26
27
28
29
30
31
 June
1
2
3
4
5
6
7
8
9
HIGH
57
70
75
78
81
77
85
86
81
84
61
67
78
83
71
85
75
LOW
33
30
45
43
40
50
49
45
48
50
49
44
44
52
48
54
40
Degree Days
10
20
31
44
61
77
91
108
123
128
139
157
167
186
193

DAY June
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
HIGH
69
73
74
69
81
81
86
91
84
76
85
88
85
88
90
93
93
92
LOW
39
36
36
41
34
42
47
48
48
48
46
50
59
59
51
50
53
55
Degree Days
197
202
207
212
219
231
247
267
283
295
310
329
351
374
395
417
420
444

DAY June
28
29
30
 July
1
2
3
4
5
6
7
8
9
10
11
12
13
14
HIGH
95
98
97
96
91
93
93
94
88
90
97
84
82
89
97
97
99
LOW
61
66
50
56
53
56
58
61
54
57
59
58
49
50
51
53
53
Degree Days
472
504
 528
554
576
601
627
656
678
702
730
751
766
786
810
835
861

DAY July
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
HIGH
98
96
89
92
91
89
84
84
88
96
71
83
88
84
91
94
97
LOW
56
57
64
60
62
61
58
56
55
53
60
56
51
53
53
52
61
Degree Days
888
914
941
967
993
1018
1039
1059
1081
1106
1121
1140
1160
1178
1200
1223
1252

DAY August
1
2
3
4
5
6
7
8
9
10
11
12
13
HIGH
78
90
84
88
85
89
87
84
76
86
90
83
77
LOW
51
46
59
56
63
68
66
52
45
40
49
52
38
Degree Days
1267
1285
1306
1328
1352
1376
1403
1421
1431
1447
1467
1485
1492

DAY August
14
15
16
17
18
19
20
21
22
23
24
25
26
HIGH
91
89
95
92
79
86
88
82
83
85
80
88
88
LOW
47
48
50
46
42
37
60
55
46
46
52
42
48
Degree Days
1511
1530
1552
1571
1581
1592
1616
1635
1650
1666
1682
1697
1715

DAY August
27
28
29
30
31
 September
1
2
3
4
5
6
7
HIGH
71
79
74
85
88
87
81
90
89
91
85
76
LOW
49
47
55
54
52
48
50
44
63
56
50
50
Degree Days
1725
1738
1753
1772
1792
1809
1825
1842
1868
1891
1909
1922

DAY September
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
HIGH
71
69
73
74
61
73
80
85
83
73
55
66
73
54
68
LOW
68
52
39
48
53
45
39
40
50
50
45
39
47
38
29
Degree Days
1943
1954
1960
1971
1978
1987
1997
2009
2025
2037
2037
2040
 2050
2048
2047

How to use Degree Days:

Some seed catalogs now give you degree day information. Let us say that you are going to plant corn and you are given the degree days for that variety of 1800. Let's say, further that instead of planting your corn on May 26, you are going to wait until June 1. The degree days for June 1, 2002 were 91. Add that 91 to your given 1800 and you will get 1891. Look at the charts above for 1891 and you will see that you could have expected to pick your corn about September 5. Of course the year 2003 or years beyond may not conform exactly to 2002. Future years may be warmer or colder. But these charts should be able to give you a close approximation for climates similar to Casper, Wyoming.

On Wind, Light, and Shade

2006: On Shade:

We think many plants would benefit from some shade and we will make a major effort to prodide that shade next season. We will place canvas on the west side of beds to shade taller plants and then place shorter plants to the east side of beds to let the taller plants shade them. This will be done for Tomatoes, Peppers, Cucumbers, and Carrots.

MORE ON WIND AND SHADE

One of my partners grows in his home garden the biggest and best tomatoes I have ever seen in Casper. He does this consistently every year. He grows the same varieties that we grow together in the plots. I think his location plays a great role in his success.

My partner grows his tomatoes in his backyard. He has terraced his slope back there and grows his tomatoes on the terraces. His L-shaped house is to the north and west of his terraces. He has a high fence completely around his back yard. His soil is naturally sandy, and with the hill and all, his drainage is superb...a factor that tomatoes love.

WIND: His tomatoes are in the ideal spot to be out of Casper's famous southwest wind. They literally get almost no wind at all.

SHADE: His tomatoes get good morning sun, but then as the day heats up, the shade from the house creeps over them, so that they get only about half a day of direct sun.

It is important to note that my partner's tomato plants still get the full heat of summer, which they love. But they also get some relief from direct sunlight for a major portion of the day. I know of another gardener whose backyard is shady all day long. He grows great peppers there. Again, his plants are definitely not avoiding the heat, but they are avoiding sunlight.

We know that these two nightshades (tomatoes and peppers) probably developed in Central America. I think the wild versions of these plants evolved at the edge of the rainforest. They got plenty of heat, but they also got some shade. Their descendents still crave that combination. I strongly suspect that other plants do too.

I first noticed that cucumbers, particularly slicers, did much better when I gave them some shade when they were very young plants.
Now we plant slicers and picklers in tubes. The slicers seem to be particularly susceptible to attack by insects when they are young. So we we place mosquito netting over their tubes. When the plant can touch the netting it is big enough to withstand the onslaught of the bugs, and we remove the netting. But the tube by itself is providing a lot of shade for both types of cucumber. Ever notice that cucumbers don't produce until they shade their own ground completely? I think they want hot days but cool soil. Maybe they need shade even beyond the 'young plant' stage.
Ever notice that carrots don't really grow bigger in diameter until they have established really good shade for their roots? This may be the same phenomena as the cucumbers above. They may need hot tops but cool roots. Please note that I am not recomending total shade. But a half day of shade may be beneficial. Carrots and cucumbers may both benefit from some partial shade.

About ultraviolet light:

WHAT IS IT?

    Like visible light, ultraviolet is electromagnetic radiation. Visible light forms a spectrum of colors that we see. On either side of this visible spectrum are infrared and ultraviolet light.

KINDS OF ULTRAVIOLET

    Ultraviolet apparently comes in three bands, or types: UVA, UVB, and UVC. UVA is not damaging to organisms, UVB and UBC are. UVC coming from the sun or outer space is completely filtered out by our atmosphere. But some UVB light does make it through our filtering atmosphere, and so it is UVB that does most of the damage we associate with Ultraviolet light in general.

DAMAGE BY UVB

WHERE IS UVB STRONGEST?

In previous remarks I have said that I think Tomatoes and other plants would benefit from some shade each day. UVB may be the culprit which is harmful to some plants we try to grow in our gardens. It is an idea which is worth pursuing.

RELATED LINKS

Ultra Violet may deplete nitrogen from soils

NASA: on Ultraviolet Light

Research on UVB being done at Colorado State University

Plants with rapid growth rate may be more sensitive to injious UVB radiation

Aluminum foil may reflect UV into insects' eyes, controlling insect-borne diseases

Short doses of UV can regulate plant growth

Tomato paste may effectively prevent sun burns

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