April 2012 / Volume 61         

In This Issue
April Lawn and Garden Tips
Spring Plant Sale!
Oklahoma Proven Shrub for 2012
Weed Control: What's it all about?
Weed Control: What's it all about?
Herbs in Your Windowsill
Summer Forcast
Ask A Master Gardener

Weather Stats for Gardeners

Soil Temperature 2" below sod:   

67 degrees 


Rainfall total last 30 days:  

6.06 inches


4 Ways to Contact Us
Email us at:

See our website at: www.tulsamastergardeners.org 

Call: 746-3701 from 9-4, M-F 
Visit us at 4116 E. 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.
Need More Information?

Click on any of the links below:


All about butterfly gardening in Tulsa County 

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.
Understanding Your Soil Test Results
Once you have collected your soil test and gotten the results back, now what? Find out here. 
How to Plant a Tree in Oklahoma Soil
Show and tell.
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 60, by size and color.
Demonstration Garden
Visit our demonstration garden on 
15th Street, open 7 days a week.  
Oklahoma Proven Plants
State horticulturists, nurseries and growers pick favorite plants, shrubs and trees for use in the Oklahoma landscape. See the winners for this year and years past.
Current and historical source of rainfall, air temperatures, soil temps and much more. Click on Bixby station.  

Back Issues  

Past issues of our eNewsletters can be read and downloaded.

Become a Master Gardener

Classes start in September. Register for more information.

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.
April Lawn and Garden Tips


  • Warm-season veggies to plant this month are most of the beans, tomato, squash, pepper and eggplant. See the Oklahoma Garden Planning Guide for specifics. 
  • Diseases which may need control this month include cedar-apple rust in apples and crabapples and fire blight bacterial disease in apples, pears, pyracantha and other members of the rosaceae family. Contact the Master Gardeners for recommendations.  


  • Bermuda lawns can be fertilized three to five times per season using one pound of actual nitrogen per 1,000 sq. ft. per application. Apply up to one pound per month April through August for a high quality lawn. Thoroughly water in nitrate fertilizers. See the Bermuda Lawn Maintenance Schedule.
  • Fertilize tall fescue lawns with one pound of nitrogen per 1000 sq. ft. this month, if you did not fertilize in March. See the Fescue Lawn Maintenance Schedule.
  • Mowing of warm-season lawns can begin now, mowing 1-1/2 to 2 inches tall. Mow tall fescue 2-1/2 inches.


  • Most bedding plants, summer flowering bulbs, and annual flower seeds can be planted after danger of frost has past. This is usually mid-April in most of Oklahoma. Plant warm season annual after the soil warms into the 60's. Log on to Oklahoma Mesonet for soil temperatures. Click here for a partial list of annuals for the Tulsa area. 
  • Let spring flowering bulb foliage remain as long as possible in order to replenish energy store in the bulb for next year. These bulbs are best fertilized either in the fall or in spring when tops first emerge using a nitrogen fertilizer labeled for bulbs. 
  • Proper watering of newly planted trees and shrubs often means the difference between success and replacement.
  • Clean out water garden and prepare for season. Divide and repot water garden plants and begin feeding fish when water temperatures are over 50 degrees F. Click here for a fact sheet on Water Gardens - A Low Maintenance Approach. 

Spring Plant Sale! 

The Tulsa County Master Gardeners Spring Plant Sale is coming up soon. This exciting annual event is the place to be for a wonderful selection of plants for your yard and your containers. These will include hard-to-find native plants, Oklahoma Proven varieties, perennials, annuals, herbs and veggies. Master Gardeners will be there to answer your questions and assist you in selecting just the right plants for your site and needs. Whether you are interested in annuals, perennials or native plants, we will have a great selection with many of our plants not widely available elsewhere.


This one day event is one you don't want to miss. Bring your friends and come early for the best selection!


Our sale will be held Thursday, April 19, from 9:00 am to 7:00 pm in Central Park Hall at the Tulsa Fairgrounds (21st Street entrance). Thank you to all of you who have already ordered plants from us this year! Please remember, you must pick up your order on April 19.


The funds earned from our annual Spring Plant Sale support the many educational services and programs offered free of charge to the public by the Tulsa County Master Gardeners. Your support enables us to continue this service...Thank you!

 Free Tuesday Evening Classes   
Tulsa Master Gardeners present the return of the Tuesday Evening Classes. Join us from 5:30 p.m to 6:00 p.m. at the Tulsa County OSU Extension Office, 4116 East 15th Street, Tulsa. Call (918)746-3701 for more information.


April 3            Fruits in the Garden  

April 10          Tomatoes- Is this the Year?

April 17          Colorful Annuals

April 24          Perennials for the lazy Gardener

May 1             Is Organic Gardening for you?

May 8             New Cultivars for the old standbys:  

Hydrangeas, Azaleas and Roses

May 15           What can we grow in the shade?

May 22           Using Shrubs as a focal Point

May 29           Our Demonstration Garden Tour

 Beware the Late Freeze!   

By taking a look around, it would be easy to surmise that spring is in full force in northeast Oklahoma, so it must be time to set out those tender, summer crops (tomatoes , peppers, squash, etc.) to get them a head start for a bountiful summer harvest. But Oklahoma weather has a way of throwing a wrench into even the best-laid plans...and one that could ruin a promising summer garden is an April freeze!


While the average last freeze date at the official observing station at Tulsa International Airport has actually just passed (March 29), remember that this site is in a more urbanized area and does not necessarily (or likely) represent conditions at your location. For practical purposes, we generally indicate April 15 as a safe time to plant frost-tender vegetables in the Tulsa area. Light freezes have occurred as late as Early May, and killing freezes (24 degrees) have occurred in early April on several occasions.


For a good example of this, look no further than the spring of 2007. That year, Tulsa saw its third warmest March, with temperatures running 15-20 degrees above normal over much of the last half of the month (sound familiar?). The warm weather lasted the first couple of days in April, then took a dramatic turn for the worse with much colder temperatures and even a little snowfall. Low temperatures fell into the mid 20s by the 8th.


If you must plant your summer crops now, be sure to have some type of frost protection handy (e.g. blanket, heavy row cover, cloches) in case of a late freeze, and keep an eye on the local weather forecasts for your area.

 Potatoes in the Garden  

Potatoes in the Oklahoma garden are a cool weather crop: the prime time for planting is when the outdoor temperatures are between 59 and 75 degrees. The variety of seed potatoes available is far greater than what is found at most stores, coming in all colors, shapes, and sizes; a good incentive to try planting these in your vegetable garden. Choose varieties according to how you plan to use them. Russets are best baked, fried, or mashed. Red skinned potatoes are good in potato salad, or can be boiled, creamed, or roasted. One pound of seed potatoes will yield approximately twenty pounds of potatoes. 

Choose a site that receives full sun with a nutrient rich, well drained soil. If you want to get a head start and plan in advance, work plenty of compost into the soil in the fall prior to planting. To prepare the seed potatoes for planting, cut them into pieces, with each piece containing two or more eyes. Plant at a depth of four inches, spacing the potatoes twelve inches apart. 

When the potatoes sprout and reach a height of eight inches, draw the dirt up around the plant, covering all but the top four inches. This is a process called "hilling." Repeat again, when the plants have grown another six inches. Potatoes grow from the lower stems; the more of the stem that is covered, the more potatoes you will harvest. 

Potatoes need one inch of water per week, and possibly more when in bloom. Monitor them periodically to ensure the soil is kept consistently moist. "New Potatoes" can be harvested from the base of the plant while it is blooming. The main crop is harvested later on in the summer when the lower leaves of the plant turn yellow. Using a shovel or cultivating fork, gently dig around the base of the plant, taking care not damage potatoes. Allow them to dry in the shade before storing.
Click here for the Potato Production Fact Sheet.

Some online sites that offer a wide variety of seed potatoes are:
The Potato Garden,  Irish Eyes Garden Seeds,  and Seed Savers Exchange  


Bt...What is it?
How does it work organically?   

Bacillus thuringiensis (Bt) is a naturally occurring bacterium common in soils throughout the world and a common bacterial disease of insects. It has been developed as an insecticide with unique properties that make it useful for pest control in certain situations. There are several strains that can infect and kill insects. Because of this property, Bt is the most common microbial insecticide in use.


Unlike typical nerve-poison insecticides, Bt produces proteins that paralyze the insect's digestive system and cause it to stop feeding and, eventually, starve to death. In order to work, Bt must be ingested by the target pest...it does not work as a contact insecticide. There are many Bt varieties, and each one will control only a few species of a specific group. Make sure the product you purchase contains the correct strain to control your particular insect problem.


Advantages: Unlike most insecticides, Bt does not have a broad spectrum of activity, so it does not kill beneficial insects, such as the natural enemies of insects (predators and parasites), or beneficial pollinators (honeybees). Therefore, Bt integrates well with other natural controls. Perhaps the major advantage is that Bt is essentially nontoxic to people, pets and wildlife.


Disadvantages: Bt is susceptible to degradation by sunlight. Most formulations persist on foliage less than a week following application. Since Bt does not kill rapidly, users may incorrectly assume it to be ineffective a day or two after treatment. However, this is merely a perceptual problem, because Bt-affected insects eat little or nothing before they die. Bt-based products tend to have a shorter shelf life than other insecticides, with reduced effectiveness after 2-3 years of storage. Liquid formulations are more perishable than dry formulations. Shelf life is longest when storage conditions are cool, dry and out of direct sunlight.


Insects Controlled by Bt include vegetable insects (cabbage worm, tomato hornworm), leaf roller, tent caterpillar, fall webworm, and the larval stage of Colorado potato beetle, elm leaf beetle, cottonwood leaf beetle and many others.

Some common trade names that include Bt as an ingredient include: Biobit, Dipel, M-Trak, Javelin, Xentari, and Thuricide.


Click here for the Biological Pest Controls Fact Sheet.

Another Hot Summer on the Way?  

After living through back-to-back cold and snowy winters in the Tulsa area, the sixth warmest winter (December-February) was a refreshing change of pace for many. And, if that wasn't enough, how about following that with the warmest March of all-time! No wonder flowers and trees (and, unfortunately, pollen) seem to be awakening much earlier than usual this year. Not only that, the rains we received in the Fall and this past month were enough to remove Tulsa County from its long-standing drought status...at least for now!


But with nightmares of 2011 weather still fresh on our minds, doesn't this make you wonder, what will the summer of 2012 be like? The official outlook from the Climate Prediction Center tilts the odds very slightly in favor of near or above normal temperatures for June through August...but more or less even odds. A slightly less scientific approach is to do a simple comparison with past years, by looking at the top 20 warmest Marches in Tulsa and seeing how the following summer stacked up.


The results were not too surprising: of the 20 years sampled, 10 of them saw above normal summer temperatures, and 10 saw below normal summer temperatures...even odds! The simple truth is, temperatures in a given season are not a determining factor for those in subsequent seasons. 


Question: I had almost no tomatoes last summer. The blossoms developed and then fell off. How can I prevent that this year?    

Answer: Your lack of tomatoes was not a unique experience last summer. At a recent horticulture conference a consensus from vegetable gardeners was that almost no one had significant tomato production during this past summer when the temperature peaked at 113 degrees. However, if the vines survived, most reported they did have tomatoes in the fall.


Even though the tomato developed in South America, it has limits as to heat tolerance. When the daytime temperature is consistently above 85 or the night temperature is above 70 during a few days, the pollen of most tomatoes becomes infertile. If the female part of the flower is not pollinated, the blossom drops from the plant and no fruit develops. Some research has shown that after as little as 4 hours of temperature of 104 or greater, tomato blossoms may be damaged and drop from the plant.


Other factors which may cause infertility and blossom drop are low night-time temperatures, low humidity, over or under watering, and too little or too much nitrogen fertilizer. Excessive nitrogen fertilizer is very common among tomato growers using the "more is better" mentality. Another cause for blossom drop is excessive fruit set. If the capacity of the plant is exceeded, the plant survives by dropping blossoms.


Strategies to cope with heat stress and summer infertility of tomato plants are several. First, if you plant earlier in the season than usual and protect plants from cold spells, this may allow fruit production before the excessive summer heat. Likewise, if you can keep your tomato plants alive through the hot summer, the cooler September weather will allow the plants to become fertile again and produce great fall tomatoes.


There are commercial sprays advertised to prevent blossom drop. These sprays have a hormone which may be somewhat effective to prevent blossom drop due to cold nights, but they will not help prevent heat damage.


Another approach is to look for one of the new heat tolerant tomato varieties. These often are labeled as "heat set, hot set or heat tolerant". There are many varieties in this group, many have "sun" in their names such as "Sunbeam", "Sunmaster" and "Suncrest" They will not be fertile at the unusually high temperatures we had last summer, but will be more productive in less extreme heat.


 Click here to send your question to the Tulsa Master Gardeners or see Answers to other Questions on the Web site