Once the seedlings have established themselves, then the plants out so that there are 2 feet (0.61 m) between them.  If you are growing the plants in containers or otherwise want the plants to remain short and stunted, it is possible to leave only 8 to 12 inches (20 to 30 cm) between each seedling. Wait until the stems of the seedlings have already developed two sets of leaves before thinning them out. Keep the healthiest, strongest looking plants and remove the weakest. Four o'clock flowers are somewhat drought-resistant, but the should not be allowed to remain dry for more than a day or two.  Try to give the plants at least 1 inch (2.5 cm) of water weekly, either by rainfall or hand watering with a hose or watering can. Note that flowers grown in a container will require more regular waterings than those grown outdoors. Choose a water-soluble, all-purpose floral fertilizer and apply it before a rainfall or when you water the plants. Choose a balanced 10-10-10 fertilizer, which contains equal parts nitrogen, phosphorus, and potassium. This type of fertilizer will promote an overall even state of health for the plant. Four o'clock flowers rarely have problems with insects and diseases, so pre-treatment for such conditions is highly discouraged. If problems do develop, treat the plants with an appropriate pesticide or fungicide. The product can either be organic or chemical. Each bush should grow a large tuber below ground. If you live in mild climates, you should be able to leave this tuber in the ground without causing damage to the plant. If you live in notably cold climates, however, you should dig it up in the late fall.  Store the tubers in between layers of newspaper in cardboard boxes or wooden crates. You can also store the tubers in peat moss or sand. Do not use plastic containers or other closed boxes, since these can encourage the tubers to rot. Place the tubers in a garage, shed, or similar environment. They should remain dry and dark throughout the winter.  Replant the tubers in the spring. Dig a hole large enough for the tuber in the same location it once grew. Place the tuber back in the ground, cover with soil, and care for the plant as before. If you do not want to dig up the tuber, you can usually protect it over the winter by covering the planting area with 1 or 2 inches (2.5 or 5 cm) of organic mulch.  Organic mulch can include leaves, grass clippings, wood chips, and newspaper. The mulch provides insulation and keeps the soil a little warmer. Note that in notably cold climates, mulch may not be enough to protect the tuber over the winter. If you are growing the plants in containers, it is also recommended that you spread mulch on top of the container during the spring or summer to help reduce the amount of water evaporation that takes place. This can help prevent the soil from drying out too severely.

Summary:
Thin out the seedlings. Keep the soil moist. Apply a mild fertilizer monthly. Treat for insects and diseases only as needed. Consider digging up the tubers before winter. Consider covering the area with mulch.