Fall Planting

Now is a good time to think about re-working or establishing raised beds in your landscape. In addition, fall is the time to plant trees in your landscape. The cooler weather we have this month is not only beneficial to the plants but also to the planter.

According to LSU AgCenter horticulturalist Dan Gill, shrubs, ground covers, vegetables, annuals and perennials should always be planted into well-prepared beds. Trees are generally planted into individual planting holes, and the soil used to fill in around their roots should not be amended. The soil of beds, however, is usually improved in some way with the addition of amendments. Soil amendments are materials blended with the soil to enhance the growth of plants to be planted in the bed. Here are the basic steps in preparing a bed.

First, do a thorough job of removing unwanted vegetation in the bed. This might mean taking up existing turf to create a new bed or just cleaning out weeds that have grown up in an existing bed. Weeds or turf grass may be removed physically or killed with a herbicide. If you are removing weeds by hand, use a shovel or trowel to get out all of the roots, rhizomes and bulbs. As an alternative, you may spray and kill the weeds with a systemic herbicide (weed killer), such as glyphosate that will not leave a residue in the soil.

When the weeds or turf have been dealt with, turn the soil over to a depth of at least 8 inches using a shovel, spade or garden fork, and break up the large clods.

Next, spread any desired soil amendments over the turned soil. You will almost always want to add two to four inches of organic matter. I think homemade compost is the best, and every gardener should have a compost pile. If you can’t make your own, you can purchase compost from local companies or city departments that produce it or bagged from your local nursery. Other suitable choices of organic matter include aged manure (available from local stables or bagged at nurseries), peat moss, soil conditioner or finely ground composted pine bark.

If a soil test indicates that your soil is alkaline (a pH above 7), sulfur, copperas (ferrous sulfate) or aluminum sulfate may be applied to make it more acid. This is especially important if you intend to plant acid-loving plants. If your soil is too acid (a pH below 5.5), lime or dolomitic lime may be applied to raise the pH and provide essential nutrients such as calcium and magnesium.

The fertility level of the soil may be improved with the addition of fertilizer. If your soil is low in phosphorus and potassium, generally choose an all purpose fertilizer with about a 1:1:1 ratio, such as 8-8-8 or 13-13-13.

If phosphorus and potassium levels are moderate to high, generally choose an all purpose fertilizer with about a 3:1:2 or 4:1:2 ratio, such as 15-5-10, 16-4-8 or something similar. Appropriate organic fertilizers could also be used. Remember, a soil test can help you decide what amendments need to be added to your soil.

Finally, thoroughly blend all of the amendments you have applied into the soil of the bed. A garden tiller is great for this step, but it can also be done by hand. Rake the bed smooth and shape the sides, and you’re ready to plant. When you finish, you will find that the bed is several inches higher than it was before preparation. This is desirable as it will help improve drainage and reduce root diseases that can cause plant death.

Garden Problems

I have seen some recent problems in home and commercial gardens. Let’s start with some problems associated with growing shallots or green onions, which are in the Alliaceae or onion family.

The fungus Alternaria porri causes purple blotch disease on shallots. This disease starts with water-soaked spots, which turn brown rapidly. As the spots expand, they turn a purplish color with darker margins surrounded by yellowish zone. These spots can become up to 1 to 2 inches. In our typical moist weather, the spots become covered with a brown dusty-appearing mold. Long periods of rain or heavy dew promote the disease.

Another fungal disease in shallots is downy mildew, which is caused by the fungus Peronospora destructor. This disease appears less frequently than purple blotch and the symptom usually appear after the leaves are six inches long and on the oldest leaves first. A white to purplish mold develops on elongated leaf spots during cool moist weather. They then will become pale green and will change to white or tan. As the leaves are affected down to the leaf sheath, they will droop over and dry up. Cool, moist weather promotes disease development- welcome to the South Louisiana winters!

Gardeners can use a fungicide containing chlorothalonil to help control both of these diseases. Always READ, UNDERSTAND AND FOLLOW LABEL directions.

The major insect pest on shallots is the thrip. The thrip is a small soft-bodied brown insect that is difficult to see. An easy way to determine if you have them is to get a white sheet of paper, place it on the ground next to the plant, lay the plant over the paper and tap the plant briskly with your hand. The thrips will be knocked off the plant onto the paper where they are easy to see.

Thrips are piercing/sucking insects that have highly developed mouth parts designed for piercing and sucking. They insert their mouthparts into the plant tissue and suck out the plant juices. High infestations of thrips can decrease the quality of the harvest.

Home gardeners can control thrips by using an insecticide such as Malathion as per label directions. There is a three-day cut off before harvest when using Malathion. Another option is to use ultra-fine oil according to the label but it may take several applications to get adequate control. When using insecticides, make sure your water pH level is between 5.5 and 6.0 for best results.

For more information on these and other horticultural topics, give me a call at 985-446-1316 or email me at bhfletcher@agctr.lsu.edu or check out our web site at www.lsuagcenter.com.