Garden Tips for March

 by David Hillock

Lawn and Turf

  • Remove excessive thatch from warm-season lawns. Dethatching, if necessary, should precede crabgrass control treatment. (HLA-6604)
  • Broadleaf weeds can easily be controlled in cool-season lawns at this time with post-emergent broadleaf herbicides.
  • Pre-emergent crabgrass control chemicals can still be applied to cool- and warm-season turfgrasses. Heed label cautions when using any weed killers near or in the root zone of desirable plantings.
  • March is the second best time of the year to seed cool-season turfgrass; however, fall is the best time to plant. (HLA-6419)
  • Cool-season lawns such as bluegrass, fescue, and ryegrass may be fertilized now with the first application of the season. Usually, four applications of fertilizer are required per year, in March, May, October, and November. (HLA-6420)
  • Begin mowing cool-season grasses at 1 ½ to 3 ½ inches high. (HLA-6420)

Flowers & Vegetables

  • Cultivate annual flower and vegetable planting beds to destroy winter weeds.
  • Apply mulch to control weeds in beds. Landscape fabric barrier can reduce the amount of mulch but can dry out and prevent water penetration. Thus, organic litter makes the best mulch.
  • Prune roses just before growth starts and begin a regular disease spray program as the foliage appears on susceptible varieties. (HLA-6403 & EPP-7607)
  • Avoid excessive walking and working in the garden when foliage and soils are wet.
  • Start warm-season vegetable transplants indoors.
  • Divide and replant overcrowded, summer and fall blooming perennials. Mow or cut back old liriope and other ornamental grasses before new growth begins.
  • Your cool-season vegetables like broccoli, cabbage, carrot, lettuce, onion, peas, spinach, turnips etc. should be planted by the middle of March.
  • Watch for cutworms that girdle newly planted vegetables during the first few weeks of establishment.  Cabbage looper and cabbageworm insects should be monitored and controlled in the garden (EPP-7313).

Trees & Shrubs

  • Prune spring flowering plants, if needed, immediately following their bloom period.
  • Plant evergreen shrubs, balled and burlapped, and bare root trees and shrubs.
  • Anthracnose control on sycamore, maple, and oak should begin at bud swell. (EPP-7634).
  • Diplodia Pine Tip blight control on pines begins at bud swell.
  • Chemical and physical control of galls (swellings) on stems of trees should begin now. EPP‑7168 & EPP-7306)
  • Dormant oil can still be applied to control mites, galls, overwintering aphids, etc. (EPP-7306)
  • The first generation of Nantucket Pine Tip Moth appears at this time. Begin pesticide applications in late March. (EPP-7306)
  • Control Eastern tent caterpillars as soon as the critters appear.


  • Continue to plant strawberries, asparagus, and other small fruit crops this month.
  • Start your routine fruit tree spray schedule prior to bud break. (EPP-7319).
  • Remove winter mulch from strawberries in early March (HLA-6214).

Establishing a new Vegetable Garden

by David Hillock

Site SelectionThe following is a list of considerations when selecting a site for the vegetable garden:

  • Sun exposure: select a site that receives at least six hours of direct sunlight each day. Southern exposures are ideal for greatest sun incidence.
  • Soil: well-drained soils such as sandy loam provide ideal conditions for growing vegetables. Soil pH near 6.6 is optimal. Avoid steep slopes where erosion will be a problem.
  • Air flow: avoid low-lying areas as these tend to collect cold air which slows germination and plant development in spring.
  • Avoid placing a vegetable garden near walnut trees. Walnuts exude a substance called juglone from their roots which is allelopathic, meaning it can kill other plants. Tomatoes and other solanaceous plants are highly sensitive to juglone.

Make sure the site is situated near a water supply.

Removing VegetationIt is important to start with a clean slate when preparing a new garden bed. And this means removing existing vegetation and controlling weeds. Usually, this is a chore for the summer prior to planting. There are several methods available to kill off vegetation. The most common method is to apply a herbicide, but there are other non-chemical methods such as solarization and smothering.

Solarization is a simple technique that captures radiant heat energy from the sun and uses that heat to kill seedlings and weed seeds, as well as some soil-borne disease organisms. Sheets of plastic are used to trap the solar heat. Solarization is most commonly used to kill weed seeds in areas where the vegetative layer has been removed.

To smother weeds, cover the soil with black plastic, or several layers of newspaper. Carpet or boards have also been used for smothering.

Solarization can combined with other control methods. For example, an herbicide may be used to make the initial kill, then solarize to control subsequent seedlings and kill seeds in the soil. Solarization can also be combined with the application of soil amendments and fertilizers. In fact, solarization can speed up decomposition of organic matter, releasing soluble nutrients into the soil.

Whatever method is used it is ideal to control perennial weeds before establishing a new garden. It will be much easier to manage them before you have the area planted with vegetables.

Soil preparationOnce the vegetation is removed, till the soil to loosen it. This is a good time to add manure or other organic material. To preserve soil structure, avoid tilling when the soil is too wet. To determine if the soil is too moist for tilling, grab a handful of soil and squeeze it slightly. If it sticks together in a ball it is too wet. If it crumbles easily it is ready.

How to Collect Soil for TestingSoil tests should be included as part of garden preparation. It is easier to amend soils and add nutrients before planting, rather than after. Soil tests collect information on soil nutrients and pH.

When collecting soil samples, test areas with drastically different soil conditions separately. To get started you will need a tool for collecting small samples. A soil probe is a great tool for sampling, if you have one. A shovel or even a small bulb planter can also be used. You will also need a bucket for sampling. You should obtain a representative sample for each area being tested. To do this, collect a number of samples from across the entire area being sampled and combine them into a single, representative sample. Take samples to a depth of six inches. In a large garden, as many as 15 to 20 cores should be taken.

Make sure to use a clean bucket that does not have any cleansers in it. Many cleaners contain chemicals that could alter your soil test results. Mix samples taken from one area together, then fill the sample bag for analysis.

Sample bags are available at your county extension office, where soil samples may also be submitted. The samples are sent to the OSU Soil, Water, and Forage Analytical Laboratory for testing. Tests cost $10 each, and evaluate soil pH, nitrate nitrogen, phosphorous and potassium contents. You can also request micronutrient tests as well as organic matter content and other specific tests. Test results include fertilizer recommendations specific to the type of vegetation growing on the site. Be sure to mark the proper space on the sample label indicating the type of area sampled, such as turf or garden.

Extension Leaflet L-249 contains detailed information on collecting soil samples.

Starting Seeds IndoorsMany gardeners choose to start their own seeds at home, rather than purchasing transplants. The advantages include savings in cost, and also the availability of a much wider selection of cultivars. You can also time seed sowing according to your expected planting date so that transplants are ready when you need them. Of course, planting seeds and tending seedlings is also a great way to spend a winter day.

You can start seeds in flats purchased from a plant supply company or garden center, you can use expandable peat pots or you can use a variety of household items. When selecting a container to start your seeds, consider drainage. We do not want water sitting in the bottom of our container. We also want to make sure the container holds enough media that it will not dry out too quickly and will have plenty of room for roots to develop.

The potting media you use is also important. Often you can find a media labeled specifically for seeding. Look for media that has both good drainage and high water holding capacity. These things seem contradictory, but we want our soil to hold adequate moisture for seeds to germinate without drying out too quickly, but we also want excess water to freely drain from the medium.

Light is often a limiting factor with starting seeds indoors. To produce hardy seedlings, you need 12 to 14 hours of light per day. Natural lighting is generally not enough. Supplement natural light using a shop light with alternating cool- and warm-white fluorescent bulbs.

To plant the seeds, sow in rows 2 to 3 inches apart. Use a fairly tight spacing within the row. As a general rule, sow seeds to a depth of approximately 3 times the diameter of the seed. Most seeds will germinate well at a temperature around 70 degrees F held constant during day and night. After germination, temperatures can be lowered according to the type of plant you are growing. Refer to OCES Fact Sheet HLA-6020, “Growing Vegetable Transplants” for ideal growing temperatures. For tomatoes, a day temperature between 70 and 80 degrees F and a night temperature between 60 and 65 degrees F is ideal.

Managing water in seed trays can be tricky. Over-watering is a common problem. The seeds do not use much water until they have germinated and seedlings are actively growing. However, the seeds need moisture to germinate. Misting the soil until it is thoroughly damp is a good way to provide moisture. Then, cover the seed tray loosely with plastic, checking soil moisture periodically. Remove the plastic once you see seedlings emerge.

Though fertilizer labels recommend weekly fertilizer applications, an application every two to three weeks is usually sufficient. The first application is not needed until seedlings are ready to be transplanted, two to three weeks after sowing.

Cutting Back Ornamental Grasses

by David Hillock

Ornamental grasses should be cut back in late winter before new growth emerges. It can also be done in fall, but the seed heads provide nice winter interest, and some birds will also feed on the seed. To make the job easier, tie up the stalks with string. Depending on the size and density of the grass, the following tools might be used: house scissors, shears or hand pruners, and electric hedge trimmers (for very large clumps). For smaller grasses, trim to about 2 to 3 inches from the ground; for larger grasses cut 6 to 8 inches from the ground. One exception is with the species Nassella (Stipa) tenuissima, Mexican Feather Grass, it does not respond well to heavy pruning and prefers to only be cut back by 1/3 to 1/2 its height.


by David Hillock

Hellebores include some 20 species of herbaceous perennials belonging to the genus Helleborus. Many hellebores are evergreen. The plants have beautiful dark green, leathery foliage year round and a winter flowering habit. The exact flowering time is variable by species, and has given us the common names used for this group, which includes Christmas Rose (Helleborus niger) for those species flowering near the Christmas season, and Lenten Rose (Helleborus orientalis) for the late winter, early spring bloomers. The flowers are indeed rose-like in appearance and nod toward the ground; however, recent breeding work has lifted the flowers more upright so we can appreciate them more when in flower.

The plants readily seed and each spring you will find hundreds of seedlings near the base of your mature hellebores. However, most of the seedlings are out-competed for light and water by the parent plant, as such, hellebores do not become weedy. If you wish to multiply the plant it is best to transplant seedlings away from the parent plant where they will not be shaded or smothered by the heavy foliage.

Hellebores, in general, require little care. They do well in the shade garden, prefer slightly alkaline soil, and only need a little pruning in early spring to remove old tattered leaves. Hellebores are also unpalatable to deer, rabbits, gophers and moles.

Upcoming Horticulture Events

Shackelford Floriculture Lecture Series
July 14, 2016
Wes Watkins Center - Stillwater, OK

Global Horticulture Conference
November 17, 2016
Wes Watkins Center - Stillwater, OK

For more information about upcoming events, please contact Stephanie Larimer at 405-744-5404.

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