Saturday, February 27, 2016 0 comments By: Ask A Master Gardener

Excess Phosphorus may be Harmful to Plants

Too much phosphorus can be harmful to plants

Bill Sevier: Ask a Master Gardener  

Saturday, February 27, 2016 1

Q: Do my roses need a lot of phosphorus to produce more blossoms? S.R., Tulsa
A: In a word, no. The effect of phosphorus on a plant’s metabolism and the amount needed by all plants is greatly misunderstood and misstated.
At least 16 mineral nutrients are needed for healthy plant growth, and the three needed in the largest amounts are nitrogen, phosphorus and potassium. These are the three numbers on fertilizer containers and are often abbreviated NPK.
Nitrogen is important for leafy growth and energy production, phosphorus is key for the storage and transfer of energy (in plants, as well as animals), and potassium is essential for many aspects of metabolism.
Nitrogen is water soluble and that which is not used by plants may be leached from the soil. Phosphorus is tightly bound by soil particles and remains in place unless used by the plant or is washed into gutters and streams. Potassium is bound to soil less tightly than phosphorus and potassium excesses are not usually harmful.
There is a belief by many that large amounts of phosphorus are needed for root growth and bloom production. It is often recommended that when planting roses or other ornamentals that a cup of bone meal or other preparations high in phosphorus be added to the planting hole.
Well-qualified horticulturists have reviewed the status of phosphorus as it relates to plant function and have stated there is no scientific evidence that excessive phosphorus is needed by roses for any reason. There is no evidence that excesses have any beneficial effect on blooming or healthy roots of plants in general — in fact, too much appears to be harmful.

No doubt all plants and animals need phosphorus for normal function. In commercial agriculture, phosphorus fertilizer is needed yearly. It is tilled into the soil but only in amounts needed for that growing season. If it were simply added to the top of soil, it would remain in place for years.
Soil tests from Tulsa-area homeowners’ lawns and gardens, performed by OSU, show adequate or more often excessive amounts of phosphorus in more than 75 percent of the tests. These excesses of phosphorus have several undesirable effects. It has been shown to interfere with a plant’s absorption of iron, manganese and zinc, resulting in yellowing of leaves and poor health of the plant.
Excesses may also interfere with the growth of beneficial fungi, called mycorrhizae. These fungi are normally present on most plant roots and assist the plant in absorbing water and nutrients. Without these fungi, plants must work harder than they would otherwise.
So before using bone meal or a high phosphorus fertilizer, do a soil test. If there is no documented need, do not use phosphorus fertilizer because it may be detrimental to your plants, and if washed into the waterways, it will result in pollution.
For more information or to ask a question about gardening, contact the Master Gardeners at 918-746-3701 from 9 a.m.-4 p.m.
Garden tips
§  The normal window for pre-emergent herbicide use is mid-February to mid-March. With the unusually warm weather we have had, it may be prudent to put out the pre-emergent earlier, rather than later, to prevent early weed establishment related to the weather.
§  By mid-February, many cool-season vegetables like cabbage, carrots, lettuce, peas and potatoes can be planted.
§  Spray peaches and nectarines with a fungicide to prevent peach leaf curl before bud swell.
§  Collect and store graft-wood for grafting pecans later this spring.

Saturday, February 20, 2016 0 comments By: Ask A Master Gardener

Oklahoma Proven Plant Selections for 2016

Best choices for planting in Oklahoma

Brian Jervis: Ask a Master Gardener

Saturday, February 20, 2016

Q: I would like to plant a perennial grass border other than monkey grass around one of my garden beds. Any ideas? Kay, Tulsa

A: If you go to the Oklahoma Proven website, you will find that among this year’s new selections are varieties of a sedge genus called Carex, which may be a good substitute for liriope (monkey grass).
Oklahoma Proven is a program that has been in place since 1999. It is organized by OSU Horticulture faculty and involves nurserymen around the state. Every year, they select a tree, shrub, perennial, annual and a “collector’s choice” plant. These plants are ones proven to grow well in Oklahoma.
The Carex selection for perennials is a large group of plants. They are sedges, not grasses, although they are similar to ornamental grasses. They may be evergreen or deciduous and have a wide range of colors. They tolerate moist and dry soils and grow in full sun and full shade. Of the many varieties, two suggested by OSU faculty are Ice Ballet and Lemon Zest. These are two of several that may be used for ground covers, perennial borders and habitat restoration.
The tree selection by Oklahoma Proven for this year is the escarpment live oak. This is a smaller version of the coastal live oak, which is the tree associated with antebellum Southern plantations. The escarpment variety is our only native evergreen oak and grows predictably in hardiness zones 6-10. The tree is more drought and cold tolerant than the coastal live oak and is tolerant of a wide range of soils. Mature height is 20 to 40 feet. It is not usually carried by local nurseries yet but is available online.
The shrub for 2016 is a yucca cultivar called “color guard.” It needs full sun to part shade and is hardy in USDA zones 3-8. The leaves are gold centered, variegated and sword shaped. Stalks emerge in late spring with creamy white bell-shaped flowers, said to be fragrant.
The annual plant selection this year are improved cultivars of annual vinca, also called Madagascar periwinkle. Improved cultivars include plants in the Cora, Mediterranean and Titan series, along with others. These plants do best with full sun and warm soils. They bloom throughout the summer and flower colors come in shades of white, pink, red and purple. Some varieties have disease resistance and drought tolerance.
The “collector’s choice” selection for 2016 are several deciduous magnolia cultivars. These trees bloom early in spring and have a tulip-like blossom, causing some to incorrectly call them “tulip trees.” They range in size from a shrub to a large tree and need full sun to part shade. They are rated for hardiness zones 4-9. Oklahoma Proven has a list of cultivars recommended on its website, and it has a wide range of colors — from red and white to pink and purple — and a new hybrid with yellow blossoms.
Go to the Oklahoma Proven website at for more information and photos of all the plants.

For more information or to ask a question about gardening, contact the Master Gardeners at 918-746-3701 from 9 a.m.-4 p.m.

Garden tips
§  Mid-February is a good time to begin pruning and fertilizing trees and small fruits.
§  Now is a good time to cut back your perennial ornamental grasses, such as pampus grass. Cut back to remove the dead grass but avoid damaging new buds and early green growth at the base.
§  Begin planting blackberries, raspberries, strawberries, grapes, asparagus and other perennial garden crops this month. Contact Tulsa Master Gardeners at 918-746-3701 for specifics about these plant

Saturday, February 13, 2016 0 comments By: Ask A Master Gardener

Use Preemergent Herbicide now to prevent Crabgrass

Now is the time to use preemergent herbicides

Bill Sevier: Ask a Master Gardener

Saturday, February 13, 2016

Q: When is it time to use a preemergent herbicide? J.T., Tulsa
A: Preemergent herbicides are helpful in preventing weed establishment. They are used in early spring (mid-February through mid-March) to prevent crabgrass and other summer weeds. They also are useful in the fall (mid-August through mid-September) to prevent winter weeds such as henbit. Some of the herbicides will need a second application in spring 60 days after the first for complete coverage of crabgrass. The label on the product will indicate if this is needed.
Many people are reluctant to use herbicides of any sort for weed control. That is a reasonable choice for those who are willing to tolerate some weeds. If you have a well-established lawn, this may prevent much of the weed invasion. A healthy thick lawn depends on good soil, proper turfgrass for the area, adequate sunlight and supplemental irrigation. Most lawns need some fertilizer, and there are organic and synthetic sources available for nutrients.
Helpful lawn maintenance calendars for what to do, what to use and when to do it for Bermuda and fescue lawns are available in the turf section of the Master Gardener website.
Master Gardeners are often asked if there are any “organic” preemergent herbicides, as opposed to commercial or “synthetic” ones. Unfortunately, while there are other organic pesticides, there is no effective organic preemergent herbicide.
Corn gluten is an organic sold as crabgrass prevention. While some reports say that if applied during a narrow window in spring, there may be some benefit; OSU turfgrass specialists cite studies that show little benefit.
For those wishing to use a synthetic preemergent herbicide, OSU has some recommendations. While there are several varieties of preemergents available on the market to prevent weeds, especially crabgrass, OSU feels that one of the many commercial brands containing either the chemicals dithiopyr, pendimethalin or prodiamine are good choices. These preemergents cost a bit more than other types but last a lot longer and, in many cases, can kill crabgrass and other weeds after they have sprouted.
The labeled directions of these products must be followed. These herbicides usually come on a dry particle such as fertilizer or other inert material. They may also be found less often as liquids. They must be washed onto the soil with at least ½ inch of water after application. After washed onto the soil, they form a barrier for weed prevention, which may last for months if undisturbed.
One of the benefits of these three products is that they are not soluble in water and do not leach into groundwater or spread from where they are applied. They are broken down in nature by sunlight and soil microorganisms.

For more information or to ask a question about gardening, contact the Master Gardeners at 918-746-3701 from 9 a.m.-4 p.m.

Garden tips

§  Most bare-rooted trees and shrubs should be planted in February or March. The roots of these plants are easily damaged and should never be left exposed to air. Plant them at the same depth as in the nursery and make sure good root and soil contact is made by gentle tamping and irrigation after planting.
§  Finish pruning shade trees, summer flowering shrubs and hedges. Spring-blooming shrubs such as forsythia and azaleas may be pruned immediately after flowering. Do not top trees or prune just for the sake of pruning.
§  Dormant oil can still be applied to control overwintering insects.

Saturday, February 6, 2016 0 comments By: Ask A Master Gardener

OSU Vegetable Fact Sheets

Find guides on caring for vegetable gardens
Brian Jervis: Ask a Master Gardener
Saturday, February 6, 2016
Q: Do you have information about when to plant different vegetables? R.M., Sand Springs
A: OSU has some excellent guides about how to grow and care for your vegetable garden. The Master Gardener office, located in the OSU Cooperative Extension Service building at 4116 E. 15th St., is a busy place in the spring and a lot of the activity is vegetable-related.
There are several useful vegetable fact sheets, which are frequently requested and are available as a free service in our office and online. Master Gardeners are available by phone or by visit in this office from 9 a.m. to 4 p.m. Monday through Friday to answer any questions that you may have about vegetables or gardening in general.
Fact sheets may be obtained one of several ways. First is directly from the office, as described above. Another way is to go to the Master Gardener’s website at and look for vegetables, found in the drop-down menu of the Lawn and Garden section. These may then be printed for your convenience. By no means are all of OSU’s useful gardening fact sheets listed there, but it includes the key ones.
Yet another route to the fact sheets is to access the “print on demand” (PODS) area on the OSU Extension website. This site gives one access to all of the thousands of OSU fact sheets. Many are related to commercial agriculture.
The quickest and easiest way to search for a fact sheet if you know the name, number or have a general idea of what you want is to go to a search site such as Google, and type in Oklahoma State and the name, number or topic of the sheet you need. This bypasses several steps for the search.
The fact sheets that are in greatest demand by vegetable gardeners in the spring are listed below with a brief description about content:
·        F-6004 Oklahoma Garden Planning Guide: This lists most all of the vegetables grown in Oklahoma and describes how and when to plant, along with days to maturity. This is the No. 1 sought after fact sheet.
·        HLA-6032 Vegetable Varieties for the Home Garden In Oklahoma: Individual varieties of a vegetable that do well in our area are listed.
·        F-6436: Healthy Garden Soils: This is an approach to preparing soils using Organic Gardening techniques.
·        F-6007: Improving Garden Soil Fertility: General information about planning a garden and correcting for any deficiencies
·        F-6033: Raised Bed Gardening: The best approach for gardening if you have unfavorable soils.
·        F-6020: Growing Vegetable Transplants: How and when to start, care for and transplant sprouts.
·        K-State: Top or Side Dressing Nitrogen Fertilizer for Vegetables and Ornamentals: While not an OSU document, this is a useful list on how, when and how much fertilizer to use on different vegetables.
Garden tips
Early February through March is the recommended time to plant strawberries. It is important to plant them in full sun and in well-drained soil. There are several types to choose from. June-bearing varieties do best in our area. They have a single crop usually early May to mid-June. Ever-bearing strawberry is another variety, which fruits May to June, a few during summer and again in the fall. The quality and size of this type of strawberry plant may not be as good as June-bearing varieties.
For full information about plant selection, planting and care of strawberries in your garden, obtain OSU fact sheet "Growing Strawberries in the Home Garden" online or in the Master Gardener office.