Monthly Horticulture Tips for September
Oklahoma Cooperative Extension Service
Division of Agricultural Sciences and Natural Resources
Oklahoma State University
Download the entire list here –> HORT TIPS SEPTEMBER 2016
- Watch for fall specials at garden centers and nurseries since fall is a great time for planting many ornamentals.
- Choose spring flowering bulbs as soon as available.
- Plant cool-season annuals like pansies, ornamental cabbage or kale, snapdragons and dusty miller when temperatures begin to cool.
- Watch for and control any late infestations of tree webworms.
- Twig girdler insects should be controlled if large numbers of small branches of elms, pecans, or persimmons are uniformly girdled from the tree and fall to the ground.
- Begin to reduce the amount of light on outside tropical houseplants by placing them under shade trees before bringing them indoors for the winter.
- You have all of September to plant cool-season vegetables like spinach, leaf lettuce, mustard and radishes, and until the middle of September to plant rutabagas, Swiss chard, garlic and turnips.
- Last nitrogen fertilizer application of the year on warm-season grasses should be applied no later than September 15. (HLA-6420)
- Winter broadleaf weeds like dandelion will begin to emerge in late September, which is also the best time to control them with a 2, 4-D type herbicide.
- If pre-emergent control of winter-annual weeds (henbit, chickweed, annual bluegrass, etc.) is desired in lawns, the application should be completed by the second week of September. Note: Do not treat areas that will be seeded in the fall.
- Continue bermudagrass spray program with glyphosate products for areas being converted over to tall fescue this fall.
- Plan to seed bluegrass, fescue or ryegrass as needed in shady areas in mid- to late-September. Fall is the best time to establish cool-season lawns (HLA-6419).
- White grub damage can become visible this month. Apply appropriate soil insecticide if white grubs are a problem (EPP-7306). Water product into soil.
Building Healthy Soils
Gardeners want a healthy soil in which to grow plants. This includes ample organic matter, good drainage, sufficient water holding capacity, a rich supply of nutrients and active biological life. Unfortunately, healthy soils are commonly removed from building sites during construction, leaving a new home sitting atop sub-soils, which are often compacted and devoid of nutrients.
Before you can build a healthy soil, you need to know what you have to work with. Soil tests are a great way to determine soil pH, nutrient contents and organic matter content. Simply feeling the soil, running it through your fingers is a good way to identify the texture of your soil. Sandy soils feel gritty and clods break apart very easily. Clay soils are sticky and clods are very hard. A clay soil can be molded in your hands. Loam soils, the ideal condition for gardening, feel smooth in your hand. They are easy to work.
Surface and sub-soil types vary significantly across the state. If you live near a river you may have a very sandy soil, while other areas have heavy clays. Fortunately, the secret to improving soil is the same for both conditions. And that secret is organic matter. Organic matter is a term used to describe living and dead materials derived from plants or animals including, compost, manure, straw, leaves, grass clippings or kitchen scraps. Organic matter enriches soils by providing a surface area where water and nutrients can bind. In clay soils, organic matter loosens structure to improve drainage. Organic matter also invites beneficial organisms into the soil. Soils rich in organic matter are going to have a darker color and many more nutrients.
Fall is a great time of year to add organic matter to the garden. It will decompose over the winter months to build healthier soils.
- HLA-6436 – Healthy Garden Soils
- PSS-2257 – Building Soil Organic Matter for a Sustainable Organic Crop Production
Plants for Poorly Drained Soils
When dealing with poorly drained soils, additions of organic matter address many of the problems faced with garden soils. But sometimes, we run into problem areas in the garden where our efforts have little impact on drainage. Areas where water often drains that are low, have poor soil, or sit at the end of a slope can be such problem spots.
In many urban sites the upper eight inches or so of the soil are in very good condition from years of compost and organic matter inputs, but when we dig deeper, we find compacted clay subsoil. This subsoil has very poor drainage. Plants often struggle to survive in these locations.
Our options for managing these sites can be limited. We could excavate the soil to 18 to 24 inches and add improved topsoil, but that can come at a great expense and can sometimes create more problems, and if we have established trees and shrubs growing in the area that is out of the question. Sub-surface drainage pipe can be installed to help pull excess water away from problem areas. And in some cases, we can just build up by installing raised beds. We can also reduce some of the water problems through careful irrigation management, but that is only part of the solution.
Another option, which is generally easier, is to plant plants that don’t mind wet feet. The following plants tolerate poorly drained soils.
- Deciduous holly, Ilex decidua
- Red buckeye, Aesculus pavia
- River birch, Betula nigra
- Bald cypress, Taxodium distichum
- Black gum, Nyssa sylvatica
- Ruby Anniversary™ Abelia, Abelia grandiflora ‘Keiser’
- Chokeberry, Aronia arbutifolia
- Summersweet, Clethra alnifolia
- Buttonbush, Cephalanthus occidentalis
- Waxmyrtle, Myrica species
- Switchgrass, Panicum virgatum
- Inland sea oats, Chasmanthium latifolium
- Feather reed grass, Calamagrostis arundinacea
- Prairie dropseed, Sporobolus heterolepis
- Sedges, Carex species
- Yarrow, Achillea millefolium
- Beebalm, Mondard didyma
- Milkweed, Asclepias spp.
- Iron weed, Vernonia lettermanii
- New England Aster, Aster novae-angeliae