Practice No. 10. Plant in the Preferred Season
Spring Planting Window
Timing may not be everything, but it's quite important. If you have just finished preparing your beds or borders and then immediately plant, the soil life needs time to “establish” along with the plant. For optimum success of cold hardy perennials, the April 1st – May 15th is the best spring planting period. Young tender plants with limited root zones need time for the root zone to grow and expand prior to the onset of summer’s day and nighttime heat, which usually begins prior to June 1st. I noticed the percentage of survivors planted after May 15th decreased dramatically, and most planted into June failed to survive at all. My typical plants sizes were 2 inch and quart-sized containers.
In beds and borders where the soil drainage and organic content is well prepared in advance (6 or more months ahead of planting), there is more leeway on planting times. Active and thriving communities of microorganisms make all the difference in a quicker establishment of your plants. Soil microorganisms do much of the work, so you don’t have to.
The section on Stepping Stones, my month to month gardening pleasures, details correct planting times for our climate for perennials, bulbs and vegetables, both cold hardy and warm season plants. Please refer to it for specifics.
February heralds the return of spring. The day, or period, of equi-umbra in Feburary is more important to me that the first day of spring. I've noticed the tipping point to warmer soil temperatures occurs about February 20-25th. Time of daylight and angle of the sun's rays (duration and intensity) reaching Earth increases to the point when one can see plant growth, providing we don't have a snow cover or colder than normal conditions. In Amarillo, day length has reached eleven hours and the sun has risen to 45 degrees at Midday providing additional solar radiation intensity. This pinnacle is called equi-umbra, or equiumbra, meaning, equal shadow -- the time when the length of the horizontal shadow of a vertical object is equal to its height; the time when the angle (altitude) of the sun is equal to 45° at its highest altitude at Midday, the solar noon or transit. The altitude of the sun at midday depends on the time of year and the latitude of any location. Locations at different latitudes have a different date for equi-umbra, in contrast to the dates for solstices and equinox shared by all.
As the soil warms up, roots really start growing. As long as we don't have a blizzard or snow cover at this time, this is about the earliest to plant trees and shrubs and other bareroot plants. One's bulbs and plants should be planted as soon as they appear in the stores. If one wants to have a spring crop of cold-season vegetables, this is the time to plant if not already done so. Covering with a grow cloth and/or poly tunnel will increase soil and daytime/nighttime air temperatures that hasten germination. Instrustions for construction a tunnel system like I use is printed at the end of the February Stepping Stones.
Bienniels like carrots and other root vegetables planted last year make a switch to flowering and setting seed. If you want to use these root vegetables as root vegetables, pick them all now, othersize let them flower and collect the seeds. Once flower/seed mode kicks in they become woody. A good source of information about vegetable gardening through fall, winter and early spring is Four Season Harvest, by Eliot Coleman.
Cool Season Plants
Cold-hardy perennials can be divided and transplanted as soon as mid-March (weather permitting), and if ordered plant shipments arrive early, once you have hardened them off, it should be safe to plant them. Again, if your soil is well amended, transplanting can be done earlier. Planting at the beginning of the planting window provides quicker establishment with less on-going maintenance (irrigating). This is due to cooler temperatures and the occurrence of springtime moisture (hopefully). There is less environmental heat stress – more energy goes into root zone development. I discourage myself from transplanting after mid-April, particularly grasses, which can be transplanted from February 20th on, at the same time they are cut back. Transplanting earlier is better than later, but each plant has different requirements. With some plants, no time is a bad time to move it, others are much more finicky. I discourage planting and transplanting container plants in the heat of summer or frigid winter months (the the possible exception for bare-root trees).
Warm Season Plants
Non-cold hardy annuals and perennials for containers are best set out after May 1st (recall the 2” snowfall Amarillo received on May 2, 2005). Plants in containers are more sensitive to environmental changes than plants rooted direct in the ground. Even nighttime temperatures in the low 50º’s are too low for tropicals. The minimum chill threshold for subtropicals is 33º – 40º. To be safe, this means the nighttime lows must be above 40 degrees for subtropicals, and above 55 degrees for tropicals to safely leave them outside. The chill threshold varies from genus to genus, species to species, and variety to different variety. Even minimum exposures of 4 – 6 hours are enough for irreversible damage to occur in the cell membranes. These temperatures may damage their tissue and stunt their growth that will not be able to be overcome. Damage to the plant includes slowed and delayed growth, delayed or no flowering, blackened and death of leaves and reduced water and nutrient absorption. If you have subtropical and tropical plants, monitor the temperatures closely and plan to move then back and forth, inside and out, or wait until May 15th.
Springtime is a busy season, not only in the garden, but also in gardener’s lives; often life preempts planting. The planting window can be left open longer under these circumstances:
- Well prepared soil a minimum of 2 ½ -3 months in advance of planting,
- Buying the perennial in a gallon or larger size container (bigger root zone),
- Planting xeric plants,
- A cooler and wetter June.
Any combination of these factors increase your success rate when planting late. Flowerbeds and borders with an active soil life for several years allow this flexibility.
Fall Planting Window
Fall planting can begin whenever summer’s heat breaks. In some years, relief comes along with Labor Day, but generally, by September 15th, it is safe to resume planting until the end of October, first part of November. Again, allow enough time for root development prior to winter’s onset (but we never know when that will be). Many books and nurserymen allow for the planting of trees and shrubs throughout winter in unfrozen ground. Trees definitely need cooler weather for planting and transplanting, mid October throughout the winter and into early spring. The end of March is the last reliable time to plant trees until October. Trees planted in summer suffer greatly and usually fail.
Bulbs, Corms, Tubers and Rhizomes
Planting bulbs, corms, tubers and rhizomes adds a lot of pop and sparkle to the floral display, similar to fireworks lighting up the nighttime sky. There is a good deal of leeway on planting bulbs. Spring flowering bulbs (spring blooming crocus, daffodils, tulips, muscari, puschkinia, scilla, hyacinths, ipheions, etc.) can be planted from mid October through December. I usually plant Thanksgiving week in November. After that, the weather is too unsure. Iris should be planted/transplanted by June to insure next year's bloom.
Summer flowering bulb planting should not begin until April 20th; May 1st is better. Summer flowering bulbs (the non-cold hardy ones – caladiums, elephant ears, spider plant, dahlia) are temperature sensitive and will rot if planted before the soil has warmed. Perennial, cold hardy summer flowering bulbs such as white rain lilies, Zephrantes candida, and the pink Naked Lady, Amaryllis belladonna, canna, Crocosmia, lilies and daylilies can be planted when purchased. Planting by late spring is more hopeful for current year bloom.
Fall blooming crocus, Colchicums, Sternbergia lutea should also be planted when purchased or when your order is received, in September for current year bloom.
Cold hardy vegetables can be planted as early as mid-February through mid-April for spring crops. Warm season vegetables can be planted beginning mid-April through mid-August. Begin seeding cold hardy vegetables around August 15th through the beginning of October for fall and winter crops. Succession planting of lettuce is recommended to insure a steady supply until spring. Row covers and poly tunnels are advised fall through early spring. Please refer to Stepping Stones section for more exact timing of specific vegetables.
Disclaimer: As always in the Texas Panhandle, our weather is unpredictable. Even with careful planning and adherence to guidelines, extreme or unseasonable weather can descend and nullify our best intentions.