newsletter logo1        
May, 2010                                                                 Number 37 
Soil temperature on May 10:  64 degrees                                Rainfall past 14 days:   0.50 inches
Ask a Master Gardener

What are the little bumps on the twigs and limbs of my Willow Oak and what can I do
 about them? 

It sounds like brown soft scale insects that have over-wintered as nymphs and are now young adults.  There are beneficial predators that will control small numbers of the pests.  Larger brown scalepopulations can be controlled with light weight horticultural oil in late winter and into early summer.  When plants are heavily infested with scales, leaves may look wilted, turn yellow, and drop prematurely.  Scales sometimes curl leaves or cause deformed blemishes or discolored halos. Bark infested with armored scales may crack and exude gum. Brown soft scale will usually not kill a plant, but large numbers can slow growth and plant vigor.  Soft scale is much easier to control with horticultural oil than the armored scale, but twigs, limbs and undersides of leaves must be sprayed.   Click here for more information.


My pond plants are a mess from last season, should I throw them all away and buy new plants? 

Now is a great time to remove potted plants from the Koi pond and divide and repot.  Plants can be made as good as new.  It is best to divide before spring growth begins. Bog plants and lilies will thrive in organically rich soil, but lotus plants prefer clay.  Convenient clay-based aquatic plant soils will work well for most all plants.   Have plenty of new baskets on hand for divisions.  pond picRemove plants from their pots and rinse pots and roots with clean water.  Carefully pull apart or use a garden shear or sharp knife to divide plant roots.  Place soil in pot allowing the crown ( that part of the stem which is at ground level) to be two inches below the basket rim. Fill  the last two inches with a fish gravel, lava rock, or river rock to hold soil in place when plants are submerged.   Some recommend liquid fertilizers or tablets, but  use sparingly to prevent algae growth in the water.

 We are past the average last freeze date of April 15 and I understand it is safe to plant tender annuals now.  A friend said that I should not plant some types of annuals yet, and to wait until mid to late May.  Which ones are they? 

Tender perennial such as caladium bicolor, Madagascar periwinkle (Catharantus roseus) and petunias (Petunia x hybrid) like their roots to be warm!  Cool soil temperatures will slow the growth of these plants and they may just sit and rot or mildew.  Late spring rains can also wreak havoc by causing root rot or fungus on leaves and stems. It is best to wait until the middle or late May when rains are fewer and the sun is warmer.  

Is it too late to plant azaleas, and what do I look for in our area?

There is no other beloved plant like the azalea and no better time to plant one.  Azaleas can be evergreen, deciduous and re-blooming.  Encore azaleas bloom in spring, mid-summer and fall and come in 24 different varieties.  There are also Kurume hybrids, Girards, and others that bloom as early as February and March, others that bloom in late spring, and still others that bloom as late as September.  By choosing cultivars that bloom at different times, it is possible to have azaleas in bloom throughout the entire growing season.  Local nurseries usually carry varieties that do well in our area.  For more information click here

Mark Your Calendar 

Tuesday Evening Gardening Classes continue at the Extension Center on 15th Street.  Free.  5:30 to 6:00. See next column for dates and topics. 

Showcase Garden Tour of six MG gardens, June 26 and 27.
4 Ways to Contact Us 
Email us at:
See our website at:
Call us at: 746-3701 from 9-4,
Visit us at 4116 East 15th Street, Gate 6 at the Fairgrounds
Whether you call or bring samples of plants to the office, trained Master Gardeners will answer your gardening questions with science based information.
Forward to a friend
If you would like to forward this issue of our eNewsletter to a friend, just click the "forward email" at the bottom of the page.
May Lawn and Garden Tips
  • Plant watermelon, cantaloupe, cucumber, squash, eggplant, okra, sweet potatoes and southern peas.
  • Bagworms may appear on juniper and Arbor vitae in late May. A botanical pesticide containing Bacillus thuringiensis (Bt) is safe and effective.
  • Lacebugs may appear on azaleas this month. Call Master Gardeners for recommendations for control. 
  • Seeding of warm season grasses such as Bermuda, zoysia and buffalograss are best done from mid-May through June. This allows enough time for winter hardiness to develop. 
  • Recycle those nursery pots from spring planting. Nurseries accepting used pots for recycling are Colebrook, Riddles, Ted and Debbies, Sanders and Southwood. 
  • Be sure to keep your newly planted trees well watered.  And don't forget to mulch around them.  The mulch should be placed like a donut, not a volcano. 
  • If you did not fertilize your cool-season grasses in March and April, do so now. 
  • Plant your summer bulbs such as cannas, dahlias, elephant ear, caladiums and gladiolus when the soil temperature reaches 65 to 70 degrees, which is usually during the last half of May.  See the answer to the question in the left column.
Free Tuesday Evening Gardening Classes

Our popular classes continue every Tuesday evening through the end of May at the OSU County Extension Offices, 4116 E. 15 Street (gate 6 at the fairgrounds).  Classes begin at 5:30 and last for 30 minutes, however, we will stay to answer questions for as long as needed.  There is no cost and no pre-registration.  Stop on your way home from work.


May 11 - Drip Irrigation

May 18 - Landscaping for Low Maintenance

May 25 - The Plants of OSU Demonstration Garden

Watch for Powdery Mildew



Powdery Mildew, major enemy of most gardeners, is a common plant fungus. Many varieties of vegetables such as grapes, squash and cucumbers are susceptible. Ornamentals commonly affected are crapemyrtles, crab apples, euonymus, lilacs, roses, photinia and zinnia.

The fungus appears as a powdery white or gray coating on leaves and stems, hence its name. It prefers warm days and cool humid nights when dew is likely powdery mildewto form-conditions found in the spring and fall. It is interesting that PM is mostly plant specific; unlikely to spread from crapemyrtles to cucumbers.

Powdery Mildew prefers to infect new growth in plants and may cause leaves and stems to twist and distort, but plants usually survive. In vegetables it reduces production and may alter the overall taste because of the stress to the plant.  The best approach to control is prevention. Many plant types at risk have PM resistant varieties which should be selected.

Other ways to help prevent any fungal leaf disease is by pruning to improve air circulation. Also, if the leaves are kept dry, this discourages any fungus growth. Water the bases of plants, not leaves. It is best to water all landscape plants, including lawns, in the mornings so they will be dry by nightfall. Most fungi grow best at night.  If an infection does develop, prune out and remove the infected parts from your landscape promptly.

Garden centers have many effective fungicides labeled for PM. However, they will only prevent new disease. Once the disease is established, there is no chemical which will cause it to disappear.  Always remember that any chemical you spray on vegetables, you will end up eating. For your health's sake, make sure the product is labeled for vegetables if you intend it for this use.

Many garden books and web sites mention the use of baking soda for Powdery Mildew. Studies have been mixed about its use and found it was best when combined with horticultural soaps or oils. Plant damage occurred when too much soda was used. So as much as one would like to use a simple safe kitchen product, be wary of possible risks to your plant.


Spring in the Square


Enjoy the flowers in Utica Square this coming Saturday, May 15th.  Master Gardeners will be available to answer your questions at their location in front of Talbots from 10 to 5.  At 12:30 Master Gardener Philip Skoch will present a seminar on drip irrigation at the stage area by Starbucks. 

Need more information?  Click on any of the links below
How to Take a Soil Test
How to collect a good sample of soil from your lawn or garden and get it tested at the OSU lab.
Trade names and where to find them   
How to Plant a Tree in Oklahoma Soil
Show and tell.
Landscaping and Gardening for Butterflies
How to attract butterflies to your garden 
Fescue Lawn Care
12-month maintenance calendar.
Bermuda Lawn Care
Ditto above.
Trees for Tulsa
A list of 50 recommended trees with descriptions.
Crape Myrtles
A list of over 100, by size and color.
Oklahoma Proven Plants
The new list for 2010.  State horticulturists, nurseries and growers pick their favorite plants, shrubs and trees.
Current and historical source of rainfall, air temperatures, soil temps and much more.  Click on Bixby station. 


Extension Logo  tulsa county logo

Oklahoma State University, in compliance with Title VI and VII of the Civil Rights Act of 1964, Executive Order 11246 as amended, Title IX of the Education Amendments of 1972, Americans with Disabilities Act of 1990, and other federal laws and regulations, does not discriminate on the basis of race, color, national origin, gender, age, religion, disability, or status as a veteran in any of its policies, practices or procedures.  This includes but is not limited to admissions, employment, financial aid, and educational services.