Horticulture 2001 Newsletter

It seems that every year about this time the rumor is resurrected that poinsettias are poisonous. This is NOT true. Though there may be an allergic reaction to the milky sap, there has never been a recorded case of poisoning. This rumor has been so persistent that members of the Society of American Florist have sought to dispel it by eating poinsettia leaves for the press.

In the 1985 AMA Handbook of Poisonous and Injurious Plants, the poinsettia "has been found to produce either no effect (orally or topically) or occasional cases of vomiting. This plant does not contain the irritant diterpenes which is the toxin in other members of the genus Euphorbia to which poinsettia belongs. (WU)

FRUIT

Winterizing Strawberry Plants

Winter can be a difficult time for strawberries in Kansas. Our plants need time to become adjusted to cold weather and will gradually become more cold resistant as the fall progresses. Strawberry plants are able to withstand colder temperatures in the middle of the winter than in the fall before they have gone through much cold weather. For example, if temperatures suddenly plummet to lower than 20 degrees F before the plants harden to the cold, they can be severely damaged and a drop to 15 degrees F may kill them. Hardened plants can withstand such temperatures with ease. This lack of hardening off may be a concern this year due to the unseasonably warm fall. If a sudden drop in temperature to below 20 degrees F is forecast, it may be wise to mulch the plants as you would for the winter. After the cold snap is over, uncover the plants so that they may continue to harden off. Normally, we mulch strawberries for the winter around Thanksgiving time. However, if we continue to stay abnormally warm, give the plants an additional couple of weeks to become cold hardy before mulching.

Mulching the plants helps protect strawberries not only from low temperatures but also from heaving damage. Heaving damage occurs when the alternate freezing and thawing common in Kansas winters heave plants out of the ground where they can die.

Wheat straw makes a good mulch and is widely available. The straw should be spread over the plants to a depth of 3 inches. Shake the slabs of straw apart so that there are no large compressed chunks.

This straw mulch not only helps protect the plants over winter but can also help avoid damage from late spring frosts by delaying blooming a few days in the spring. Mulch should be removed gradually in the spring as the plants begin new growth. Remove enough so that the leaves can be seen. Leaving some mulch in place keeps the berries off the ground and conserves moisture. Also, mulch left in the aisles helps protect pickers from muddy conditions. (WU)

MISCELLANEOUS

Soil Tests and Plant Growth

Though soil tests are useful for identifying nutrient deficiencies as well as soil pH, they do not tell the whole story. We often receive soils from gardeners that are having a difficult time growing crops even though the soil test shows that nothing is deficient. Following are some factors that can affect plant growth that are not due to nutrient deficiencies or pH.

Too much phosphorus: Most Kansas soils are naturally low in phosphorus. However, soils that have been fertilized for a number of years may have phosphorus levels that are quite high. As a matter of fact, the majority of soil tests we receive show phosphorus levels in the "high" category. Too much phosphorus can interfere with the uptake of some micronutrients such as iron, manganese and zinc. High phosphorus soils should only be fertilized with fertilizers that have relatively low amounts of phosphorus.

Not enough sun: Plants need a certain minimum amount of sun before they will grow well. As a general rule, flowering (and fruiting) plants need at least 6 to 8 hours of full sun per day. There are, of course, exceptions such as impatiens that bloom well in shade. Move sun-loving plants out from the shade or use plants that are better adapted to shady conditions.

Poor soil physical characteristics: Roots need oxygen as much as they need water. A tight clay soil can restrict soil oxygen levels as well as make root penetration of the soil difficult. Increasing the organic matter content of clay soils can help break them up. Add a 2 inch layer of organic matter and till it in.

Walnut trees: Walnuts give off a natural herbicide that interferes with the growth of some plants such as tomatoes. Vegetable gardens should be at least 50 feet away from walnut trees if possible. For a listing of plants that are susceptible to walnut, go to:

http://www.gov.on.ca/OMAFRA/english/crops/facts/info_walnut_toxicity.htm

Tree roots: Trees not only compete with other plants for sun but also for water and nutrients. Extra water and nutrients may be needed.

Shallow soils: When new homes are built, the topsoil is often stripped off before the soils are brought to grade. Though the topsoil should be replaced, it sometimes is not or is not replaced to the same depth as it was originally. You are left with a subsoil that usually does not allow plants to grow well due to a lack of soil structure. Adding topsoil to a depth of 8 to 12 inches would be best but this often is not practical. In such cases, try to rebuild structure by adding organic matter and working it into the soil.

Improper watering: Roots develop where conditions are best for growth. Shallow, frequent watering leads to roots developing primarily near the surface of the soil where the soil is moist. Such shallow root systems are easily damaged by heat and any interruption in the watering schedule. It is better to water less frequently and to a greater depth to encourage a deeper root system that is less sensitive to heat and water stress.

Watering during the evening can also be detrimental to plants if the irrigation wets the foliage. Many diseases are encouraged by free water on the leaves. Watering late in the day often will keep the foliage wet until dew forms. Dew will keep the foliage wet until it evaporates the next morning. It is better to water early in the morning so leaves do not stay wet as long. If you must water late in the day, use drip irrigation if that is practical (such as in a vegetable garden). (WU)

Water Landscape Plants Before Winter