Horticulture Tips for April 2017 presented by the Horticulture and Landscape Architecture Department, the Oklahoma Cooperative Extension Service, and the Division of Agricultural Sciences and Natural Resources at Oklahoma State University.

Garden Tips for April by David Hillock

Fruit and Nut

  • Don’t spray insecticides during fruit tree bloom or pollination may be affected. Disease sprays can continue according to schedule and label directions. (EPP-7319)
  • Control cedar-apple rust. When the orange jelly galls are visible on juniper (cedar), following a rain, begin treating apple and crabapple trees with a fungicide. (EPP-7319, EPP-7611)
  • Fire blight bacterial disease can be controlled at this time. Plant disease-resistant varieties to avoid diseases.
  • Continue spray schedules for disease prone fruit and pine trees.

Tree and Shrub

  • Proper watering of newly planted trees and shrubs often means the difference between success and replacement.
  • Remove any winter-damaged branches or plants that have not begun to grow. Prune spring flowering plants as soon as they are finished blooming. (HLA-6404, HLA-6409)
  • Control of powdery mildew disease can be done with early detection and regular treatment. Many new plant cultivars are resistant. (EPP-7617)
  • Leaf spot diseases can cause premature death of foliage and reduce plant vigor. 


  • Most bedding plants, summer flowering bulbs, and annual flower seeds can be planted after danger of frost. This happens around mid-April in most of Oklahoma. Hold off mulching these crops until spring rains subside and soil temperatures warm up. Warm-season annuals should not be planted until soil temperatures are in the low 60s.
  • Harden off transplants outside in partial protection from sun and wind prior to planting.
  • Let spring flowering bulb foliage remain as long as possible before removing it.


  • Wait a little longer for it to warm up before planting cucurbit crops and okra.
  • Plant vegetable crops in successive plantings to ensure a steady supply of produce rather than harvesting all at once.
  • Cover cucurbit crops with a floating row cover to keep out insect pests. Remove during bloom time.
  • Watch for cutworm damage and add flea beetle scouting to your list of activities in the vegetable garden

Garden Planting Guide for Warm-Season Vegetables (chart)

Garden Planting Guide for Warm-Season Vegetables

*These dates indicate planting times from southeast to northwest Oklahoma.  Specific climate and weather may influence planting dates.  For cool-season vegetables, the soil temperature at the depth where the seeds are planted should be at least 40°F.


  • Warm-season grass lawns can be established beginning late April from sprigs, plugs or sod. (HLA-6419)
  • Fertilizer programs can begin for warm-season grasses in April. The following recommendations are to achieve optimum performance and appearance of commonly grown species in Oklahoma.

      - Zoysiagrass: 3 lbs N/1,000 sq. ft./year
      - Bahiagrass: 3 lbs N/1,000 sq. ft./year
      - Buffalograss: 2 - 3 lbs N/1,000 sq. ft./year
      - Buffalograss/grama mixes: 3 lbs N/1,000 sq. ft./year
      - Bermudagrass: 4-6 lbs N/1,000 sq. ft./year
      - Centipedegrass: 2 lbs N/1,000 sq. ft./year
      - St. Augustinegrass: 3-6 lbs N/1,000 sq. ft./year

  • When using quick release forms of fertilizer, use one pound of actual nitrogen per 1,000 sq. ft. per application; water in nitrate fertilizers. (HLA-6420)
  • Mowing of warm-season lawns can begin now (HLA-6420). Cutting height for bermuda and zoysia should be 1 to 1½ inches high, and buffalograss 1½ to 3 inches high.
  • Damage from Spring Dead Spot Disease (SDS) becomes visible in bermudagrass (EPP‑7665). Perform practices that promote grass recovery. Do not spray fungicides at this time for SDS control.
  • Grub damage can be visible in lawns at this time. Check for the presence of grubs before ever applying any insecticide treatments. Apply appropriate soil insecticide if white grubs are a problem (EPP-7306). Water product into soil.

Landscape - General

  • Hummingbirds arrive in Oklahoma in early April. Get your feeders ready using 1 part sugar to 4 parts water. Do not use red food coloring.
  • Keep the bird feeder filled during the summer and help control insects at the same time.
  • Lace bugs, aphids, spider mites, bagworms, etc. can start popping up in the landscape and garden later this month. Keep a close eye on all plants and use mechanical, cultural, and biological control options first.
  • Be alert for both insect pests and predators. Some pests can be hand picked without using a pesticide. Do not spray if predators such as lady beetles are present. Spray only when there are too few predators to be effective. 

All-America Selections present both Regional and National Winners for 2017

All-America Selections (AAS) judges have again finished a rigorous year of trialing and now the AAS Board of Directors is pleased to announce the newest AAS Winners. A few years ago the organization began recognizing regional performance; the entries that did well in a majority of regions are designated as traditional National Winners.

At the beginning of 2017, seventeen plants made it on the National Winners list with ten vegetables and seven flowers. Vegetable selections include Bean (Pole) Seychelles, Fennel Antares F1, Okra Candle Fire F1, Pepper Aji Rico F1, Pepper Chili Pie F1, Pepper Mad Hatter F1, Tomato Midnight Snack F1, Tomato Patio Choice Yellow F1, Watermelon Gold in Gold F1, and Watermelon Mini Love F1; the flowers include Celosia Asian Garden, Dianthus Supra Pink F1, Geranium Calliope® Medium Dark Red, Verbena EnduraScape™ Pink Bicolor, Vinca Mega Bloom Orchid Halo F1, Vinca Mega Bloom Pink Halo F1, and Zinnia Profusion Red.

The Regional Winners include an additional seven plants, five vegetables and two flowers. Winners include Pea Patio Pride (Regional-Southeast), Pepper Sweetie Pie F1 (Regional-Heartland, Northeast, Southeast), Squash Honeybaby F1 (Regional-Heartland), Squash Sugaretti F1 (Regional-Southeast), and Tomato Chef’s Choice Yellow F1 (Regional-Southeast) as the vegetables, and Penstemon Twizzle Purple (Regional-Heartland and Southeast) and Petunia Evening Scentsation F1 (Regional-Heartland, Greatlakes, West/Northwest) as the flowers.         

All of these winners were trialed next to similar varieties that are currently on the market. The AAS Judges do a side-by-side analysis of growth habit, disease resistance and more to determine if these entries were truly better than those already available to home gardeners. Only those flower entries with superior garden performance or the vegetables with superior taste and garden performance are given the AAS stamp of approval.

A complete list of all AAS Winners since 1932 can be found here:  

A complete list of trial grounds and judges can be found here: 

All-America Selections® was founded in 1932 and continues as the oldest independent testing organization in North America. Every year, new, never-before-sold varieties are trialed in our Trial Grounds and professional horticulturists determine which varieties will be deemed winners based on their garden performance. AAS relies upon a public relations program to inform gardeners about AAS Winners that are announced three times each year.

Using Bedding Plants in the Landscape!

by David Hillock

Bedding plants or annuals continue to be a garden favorite because they can provide a full season of color and interest. They also have many uses, to name a few – temporary ground covers, hanging baskets, containers, dried flowers, cutting gardens, wildflower gardens, bedding plants, etc. The following tips will help to ensure a successful and stunning display.

Bed Preparation - The real key to a successful planting is proper bed preparation. Remove all debris and gain control of weeds before planting. Choose a suitable site: i.e. – sun, shade; close to a water source; and away from shallow rooted trees and shrubs, which compete for water and nutrients. Soil tests are recommended to determine proper amounts of fertilizer to apply. Often gardens need only applications of nitrogen. Amend soil by incorporating 3 - 4” of composted organic matter into the area; this improves soil aeration, improves drainage, encourages healthier root systems, and is easier to plant and manage. Spade or till in the organic matter at least 6” deep. After planting, apply a light mulch a couple inches thick if necessary. Mulches can aid in shading out weed seed as well as moderating soil temperatures and moisture. 

Timing – In Oklahoma, planting times will vary some depending upon which part of the state you live in. In the north central portion of the state the middle to latter part of April is the time to begin planting many of the annuals available in your garden center or nursery. Southeast residents may be a week earlier and northwest residents may be about a week later. Remember that these planting times are based on average last frost dates. The planting of flowers like Catharanthus roseus (Annual Vinca) should be delayed until warmer weather is sure to stick around and the soil temperatures are at least 65°F or better.

Design - a living bouquet – While the following are not necessarily hard and fast rules and may create a bit of a challenge for some of us, it is certainly worth the time and effort when the right “combination” is achieved. Take time to plan the design properly. Take into consideration cultural requirements, principles of color, and placement of different species. Also, don’t be afraid to copy what others have already proven to be successful. 

Avoid planting monocultures (beds with all of the same species e.g. – all vinca or all marigold, etc.) or monochromatic gardens (all one color). Instead, try combining several annual species into one design. The benefits of mixing several species together are twofold: 1) it adds interest (height, color, and texture differences) to the garden and is pleasing to the eye. While the flower and color in themselves are beautiful, using just one flower and/or color will not hold one’s interest for very long. 2) At the same time, you protect yourself from total failure due to a pest particular to one species that could wipe out the whole bed. Mixing species and/or cultivars provides genetic diversity, which reduces the chances of an insect or disease to become well established in a bed.

Group plants that have the same cultural requirements to increase success; make sure you select those species best suited for the site i.e. sun, shade, wet, or dry (HLA-6425). Do not place plants that thrive in cool, moist shade into a bed in full sun and little water.

Working with colors can be tricky, but by using the following principles and tips, and some practice, you will soon be creating some wonderful bouquets.

  • The color wheel is divided into cool and warm hues, using three primary colors – red, yellow and blue. Cool colors such as blue, green and violet are subdued. Warm colors such as red, yellow and orange tend to catch the eye more easily.
  • Color groupings can be harmonious or contrasting. Hues are particular shades of colors.  Hues in any neighboring group on the color wheel are harmonious or analogous. Complimentary contrasts are formed by choosing colors opposite each other on the color wheel.
  • A successful design will have a balance of analogous and complimentary contrasts.
  • White, silver or gray, and yellow should be used sparingly since they have a tendency to drown out the rest of the design. These colors can be used as a “sparkle” and in general should not make up more than 10 percent of the composition.

In general, flowers need to be planted in drifts or clumps large enough to make a visual difference when viewed from the farthest vanishing point. Of course this may not be practical as dictated by the pocket book. But large masses of flowers are more dramatic and satisfying.

Color balancing and strategically placing the dominant colors in the composition or throughout the garden will lead the eye from one end of the bed or garden to the next.

Color balancing can be used to trick the eye into thinking that the garden is deeper or larger than it really is. By using bright strong colors close to the viewer, and then getting progressively bluer and grayer and lighter as you go further back, you can create the illusion of depth.

Height differences can also be used to exaggerate depth by emphasizing the height differential between the little plants in front and the tall ones in the back. The ever-increasing height allows more of each color to be seen enhancing the overall effect.

In general, small or short plants are placed in the front and tall ones in the back. However, more interest can be created by bringing some of the tall plants closer to the front and pushing short ones toward the back. Some successful combinations for partial or light shade might include: begonia, impatiens, lobelia, wishbone flower and a touch of marigolds for sparkle; for sun you might use combinations of: blue salvia, summer snapdragon, vinca, Joseph’s coat, and use zinnia and dusty miller for sparkle.                                             

How many bedding plants do I need? – Avoid overbuying or under-buying the number of bedding plants you need. All it takes is some simple arithmetic.

1) Measure the area of your garden and calculate its square footage (width x length = square feet). If the area is irregularly shaped – oval, round or long and winding – a rough estimate is good enough.

2) Use the chart below to estimate the number of plants you will need. You will probably want to get at least a few more than you will need, just in case some are damaged by weather, animals or pests.

                           Recommended Spacing                   Number of Plants per Sq. Ft.

                                      6 inches                                                     4

                                      8 inches                                                     2.25

                                    10 inches                                                     1.44

                                    12 inches                                                     1

                                    18 inches                                                     0.44

                                    24 inches                                                     0.25

Example: A 125 sq. ft. garden, using plants recommended to be spaced 10 inches apart would need approximately 180 plants.

The above information is only the tip of the iceberg. For more information and ideas look for books that discuss the principles of design and color and study them, or visit your local public gardens or retail garden centers for their expertise. Oh and don’t forget, Have Fun!

 Tomato Cages

by David Hillock

Tomato cages are very beneficial to the production of your tomatoes. Not only do they provide a support for indeterminate types to sprawl upon, but they also keep the fruit off of the ground and provide better air circulation through the plants thereby reducing chances of disease development. By encouraging vertical growth, you can also grow more in smaller spaces. 

Though manufactured cages are available for purchase, some are even quite ornamental, you can build your own. Any strong material can be used including wooden stakes or wire fencing/mesh. Wooden stakes about 6 feet long should be used. Tie the plant to the stake as it grows. Wire fencing/mesh cages should be about 18 to 25 inches in diameter and 3 1/2 to 5 feet tall. Use concrete reinforcing mesh, 10-gauge wire frame or other sturdy wire mesh that has openings of at least six inches. These larger openings allow you to reach in and harvest fruit more easily. Cut and bend the mesh into cylinders fastening the ends together. Snip off the bottom one or two rungs. By cutting off the bottom one or two rungs, the cage can be pushed into the ground at least six inches deep around each plant.

Watering Time Affects Slug Population

by David Hillock

Several years ago researchers in Switzerland examined irrigation timing effects on slug damage to lettuce plantings. Overhead irrigation in the morning (2 hours after sunrise) resulted in significantly less feeding injury to lettuce plants than watering in the evening (2 hours before sunset). So, morning watering not only cuts down on diseases, it may cut down on slug damage too.

Selecting New Vegetable Crops

by Lynn Brandenberger

Whether you are a vegetable farmer or a home gardener most of us are interested in new and different crops.  Maybe, just maybe we’ll find something that’s easy to grow, nutritious, and popular for either the table or the market.  The great thing about the vegetable world is that there are over 40 crops to choose from, so surely we can find something that will knock our socks off!

We can start our search based on when we hope to grow the crop.  First question: Warm-season or cool-season crop?  We have super stars for each season.  At issue here is: When do you prefer growing crops, does your market have a big open spot during a specific season that no one is currently filling and you could make money during that time? 

Another question that you need to ask yourself: How difficult is the crop to grow?  Realize this, some crops require less management while others are challenging even for growers that have grown them for years.  A couple of examples of this would be leafy crops vs. fruiting crops.  With leafy vegetables you normally direct seed and once you have a good stand you will keep an eye on water, fertility, and potential pests.  Fruiting crops can be direct seeded or transplanted, but you need the crop to flower, set fruit, and mature the fruit in addition to the cultural issues that we mentioned for leafy crops.  Fruiting crops normally take more time and potentially have more risk since there is more that needs to happen to grow and produce the crop.  Crop inputs including water, fertilizer, etc. vary greatly between crops and you may want to consider the cost and need for these essentials when selecting a crop.  For more information on crop basics check out E-995 Oklahoman’s guide to growing fruits, nuts, and vegetables, available at:  

Along with thinking about growing the crop you may also want to consider the nutritional profile of the crop that you will be producing.  In other words what types and amounts of nutrients will the crop provide to those that will be eating it.  USDA has a great website for this called the Food Composition Database.  This site is available to anyone and has the nutritional content of everything from cereal, cookies to specific vegetables.  The web address for USDA’s Food Composition Database is

Last, Realize that it is best to start small with a new enterprise (crop in this instance) and learn how to grow it.  You will make mistakes as you learn, so if you have a small planting and you lose it all to a problem it won’t cost you nearly as much.  Long story short, don’t bet the farm on a new crop until you have some experience with it. 

Summing up, making decisions about a new crop includes determining when you will want to grow it, considering how it is grown and how that works with your current experience, how the crop adds up nutritionally, and last allowing time to learn how to grow it before you grow it on a larger scale.

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