By Urban Harvest
Different vegetables originated in particular world biological regions (or biomes), so they generally grow best in those conditions. In many respects, successful vegetable gardening here hinges on our understanding of these origins especially the temperatures.
Annual vegetables and fruits need to be planted at the right time to exploit their preferred temperatures. The right time is when soil and air temperatures promote growth and will be for the 2-6 months the plant will live.
As well, for some plants, it is important that air temperatures be right for pollination to occur; for others, day length must be correct.
In our area, gardeners need to plant tropical vegetables and annual fruits when it will be hot for the lifetime of the plant so okra, sweet potatoes, southern peas, butter peas, long beans, eggplant, basil, and tropical gourds need tropical heat only, so are best planted in May to produce all summer.
Cucumbers, squashes, watermelon and cantaloupe all get planted as soon in the spring as they will grow, which is in late March to April. They will thus be large productive plants by late June when we have the most hours of heat.
Vegetables from warm (but not hot) summer biomes need to grow and produce during the relatively brief periods of spring and fall when our high temperature is between 65-85 and our lows are above 55. So plants like green beans, for example, should be planted in March or April.
In spring, Houston highs average above 65 after Feb. 5, but nighttime lows are still below 55 until April 1. By then, highs are about 76. Highs get above 85 on May 16 when lows are 66. So the good dates for warm vegetables are just six weeks from April 1 to May 16. These temperatures will occur a few days earlier in inner city locations, southern Houston, and Gulf shores; and 2-4 weeks later in colder parts of Montgomery and other counties well north of Houston.
Bush beans, however, need seven weeks to produce and pole beans nine, and will produce for two months perhaps if temperatures aren't too hot. So beans need to be planted in early March or late February to get high production.
To flourish, sweet corn must have low temperatures above 59, and high temperatures between 66 and 95. So corn can be planted from March all the way to June or even later in cooler places. But in inner city areas, the urban heat island makes 98 summer temperatures much more likely, so planting mid-March to early April is best.
Tomatoes and peppers can be long-lived plants. However, they do not grow in cool or cold weather, die at temperatures just below freezing, and pollinate their flowers only when temperatures are warm but not hot. Tomato blossoms fall off unpollinated when nighttime temperatures are higher than 70-76 or lower than 55, or if day temperatures are much above 85. Sweet peppers can pollinate as low as 64 but stop pollinating when temperatures are above 82.
Tomatoes and peppers need about three months growing above 55 to flower. Temperatures are right for pollination by April 1, with occasional good growing conditions before this in March, so plants covered with flowers about March 15 will usually produce the most fruit. In order to achieve this, indoor grown transplants need to be set out in Central Houston the second or third weeks of February and then protected well from nighttime cold. To learn more about tomatoes, Urban Harvest offers a Growing Great Tomatoes class, Saturday, Feb. 14, at the University of Houston. Register at urbanharvest.org/classes
Do this with protective devices. Best by far is the Aqua Dome; less effective and durable, but less expensive is the Wall of Waters; still less effective is a homemade device: place a gallon plastic jug of water next to the plant, surround with a tomato cage, then wrap with transparent plastic or spun polyester row cover, and fix with wooden clothespins or twine.
This column is produced by Urban Harvest. Learn about gardening classes, community gardens and orchards, farmers markets and more at Urban Harvest website. Article is written by Bob Randall, Ph.D., who is the former executive director and a cofounder of Urban Harvest. He is also the author of "Year Round Vegetables, Fruits and Flowers for Metro-Houston". You may contact him at YearRoundGardening@comcast.net.