The sun is everyday moving Northward. The days are growing longer. We are rapidly approaching the first official day of Spring (March 19th this year), the moment when the night is as long as the day (the equinox). The desire to be outside increases. My Audible Spring Onset Indicator (the volume of child-generated noise at the parks and at the school playgrounds) is now telling me Spring is near as we reach a high today of 70 degrees F.
Measure soil temperature to determine when to plant
The easiest and most reliable way for me to advise you of when to plant is by measuring soil temperature. You may do this using a soil temperature probe or, lacking that, a BBQ temperature probe may do the job. Use your judgment to see if the reading makes sense. Below are my temperature measurements using a BBQ temperature probe.
Front yard, South side of house, in full sun, next to house, 44 deg. F
Front yard, South side of house, in full sun, next to street, soil covered by leaves, 41 deg. F
Back yard, North side of house, in partial sun, next to West fence (tulips beginning to emerge), 37 deg. F
You can put these in the ground this spring (my favorites are underlined)
When soil temperature climbs to…
about 2/3 of these seeds will germinate.
45 degrees F
| Beets |
|
Carrots, Danvers Half Long
|
| Lettuce |
|
Lettuce, Butter-head Butter-crunch
|
| Lettuce, Ruby Leaf |
| Parsley, Italian |
| Parsley, Moss Curled |
| Radishes |
| Spinach, Bloomsdale |
50 degrees F
| Arugula |
| Broccoli* |
| Cauliflower* |
| Collard greens |
| Kale (Premier) |
| Kohlrabi |
| Mustard |
| Mustard (Tatsoi) |
| Pea |
| Rutabaga |
| Sunchokes |
| Turnip |
54 degrees F
| Swiss Chard |
| Swiss Chard, Bright Lights |
*Broccoli and Cauliflower take a large area for the amount of food they produce, and broccoli is challenged by our temperature swings from cold to hot as well as significantly damaged by the cabbage moth. I find other crops yield more food more easily in that amount of growing space. But don’t let this discourage you. You certainly can be successful growing broccoli and cabbage if you’re willing to make the investment.
Keep your planted seeds warm and watered
The key to good germination is proper soil temperature and constant humidity. If the soil is too cold or the seeds dry out, they will not germinate.
A deciding factor of when to plant is answered partially by asking, “When do I want to start watering?” While there is danger of irrigation piping freezing, you will need to water by hand.
Water daily or use a thin plank of wood and/or horticultural blanket to cover until germination. Check under the cover daily to see when germination occurs, then remove wood plank and water daily until roots grow deep enough to no longer be effected by daily desiccation of the soil surface. If you’re going to use a wood plank, make sure it is not so big and thick that the soil cannot stay warm.
What to expect
Always work to improve your soil
Most natural soils that I’ve encountered in the High Plains are dense clay. Work in materials that will allow water to drain. The most nutritious supplement you can add is clean compost – black, rich, broken down organic matter, aged and weed-free, low in salt. I make my own from yard waste and kitchen scraps, and I add rabbit manure when I want to heat up the batch and get it processing faster. Most people throw in the trash what I use to make my compost. I never send a fallen tree leaf or anything else organic off of my property (unless it is diseased, painted on, or in some other way unclean or undesirable). In that case, I send it to the trash or to be recycled.
If you don’t have your own compost, just buy good quality organic compost. If your soil is dense clay, then dig and mix in about 1/4 by volume. If your soil already has some organic matter in it, then plant your seeds or seedlings and use the compost as a topdressing or mulch. This way, you won’t disturb the delicate filaments of the mycorrhizal fungi already established in the soil. The fungi help bring nutrients to your plants and increase your yield.
The Burning Heat and Dryness Will Soon Come
We plant our cool season crops as soon as possible because by late-June, many of these crops (especially lettuce) will be suffering from the heat and cannot continue to deliver good produce.
Whenever you put your seeds in, try to do it preceding a storm that will bring precipitation. Then be ready to hand water daily until germination to keep the top layer of soil moist. Be careful with clay soils that you don’t make it too wet. Over-watering causes the roots to suffocate and rot.
Understanding Solar Power in Food Production
Plants need both light and heat. A horticultural blanket allows the light through to the plant while keeping it warm at night or when a cold front moves in. This makes it a wonderful and simple season extender. Your plants will be happier and more productive before your last frost date covered in one of these blankets. The diffuse solar radiation and added warmth will create a more moderate, less extreme, climate for them to thrive in.
More solar energy means more power and more food. At 40 degrees North latitude (Denver’s approximate latitude), the shortest day delivers about 150 Watts/square meter/day of solar insolation. The longest day delivers over 450 Watts/square meter/day (triple that received in winter). At the Vernal (March) Equinox the solar energy will be 300 Watts/square meter/day.
At 300 Watts/square meter/day, we can produce lovely leafy greens, especially during the cool season.
At 450 Watts/square meter/day during the warm season, we can grow amazingly productive squashes that put out their leaves like massive deployed solar panels. But another warm season crop, basil, is overpowered by our sunshine. It will do better and produce larger leaves under filtered light as might be found under a locust tree or produced artificially with shade cloth.
In Conclusion
When your plants have the right amount of light, warmth, moisture, and nutrition, they will have what they need to thrive. My soil temperature is telling me to wait just a little longer before planting my seeds outdoors.