Gardening Help FAQs

Here are answers to some of the most common questions we receive about garden plants. You will find concise information on general gardening techniques as well as plant selection and care. For detailed information on specific plant pests and problems refer to our Common Garden Pests and Problems page.

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Horticulture Questions and Answers

When can I plant in St. Louis?

Most planting activities revolve around the average last killing frost in the spring. In St. Louis this date is considered to be April 15. This is an average and the actual date of the last killing frost will vary from year to year. With April 15 as your target date, seeds and transplants of hardy vegetables can be planted around March 20th. This includes: lettuce, radishes, peas, spinach, mustard greens, collard, beets, carrots, potatoes, onions, early cabbage and broccoli. Pansies can also be set out at this time. After the threat of frost is past and the soil is warm, around May 1, set out tomatoes, and plant seeds of beans and corn. This is also a good target date for starting to set out bedding plants such as marigolds, salvia and impatiens. When the weather and soil is warm, around May 10th, plant heat loving plants such as cucumbers, eggplants, okra, sweet potatoes, watermelons, peppers, summer squash and zucchini.

For fall vegetable gardens determine how many days the vegetable needs to mature and work backwards from October 20, the average first killing frost in the fall. Add a couple of weeks to compensate for the shorter days of fall. For most vegetables this will place planting between mid-July and mid-September.

Planting dates for trees, shrubs and perennials can be more variable but there are few guidelines to follow. First, plant as early in the spring as you can. Generally, planting can be started in March and should be concluded at least by early June. Trees, shrubs and perennials planted early will have more time to develop a good root system before the hot St. Louis summer arrives. As soon as the ground can be worked, bareroot, balled and burlapped and container grown plants can be set out. Delay planting, however, if the soil is wet and will compact during planting. Summer planting of balled and burlapped and container-grown plants can be done but follow-up care is very important as the plant's root system may be inadequate to deal with the water demand of the leaves. Dropping of leaves or browning leaves may be the result. Mulch well and check weekly for watering. If the plant is dry, water thoroughly.

Fall planting should not be overlooked. Many hardy plants which are well adapted to the area take very well to fall planting. After the leaves have fallen from deciduous plants they can be dug and moved. The cool soil temperatures of fall are ideal for root formation. Conifers, such as pines and spruce can be moved in late September or early October. Tender plants or plants which are more difficult to transplant are best planted in spring, as are those plants which may have their young roots broken by heaving caused by the freezing and thawing of the soil in winter. To help guard against heaving, mulch the plants well and check them periodically to make sure they are not being pushed out of the ground. If they are, press them back down into the soil and firm the soil around the root ball. Other plants which may not transplant well in the fall are those which can rot easily if their roots are in wet, sodden soil.

One final reminder. Most failures with planting are generally caused by choosing a plant which is not well suited for the site and poor follow-up care. For success, select plants carefully, mulch after planting, check them at least once a week, and water if necessary until well established.