Issue: July 12, 1999

Plant shrubs in summer?

Is it too late to plant shrubs in the landscape? I had wanted to plant some low water plants but got busy. I hope I still have time.

No, it is not too late, especially for many of the shrubs used in xeriscapes. Many of these, especially those native to New Mexico, are genetically programmed to grow during our monsoon season, so this is a good time to be planting them. If the monsoon rains are productive this year, you will need to irrigate less to establish the plants, though you will still need to irrigate. If the monsoon rains are rare, then you will need to irrigate regularly to establish the plants.

Establishment of these plants means development of an adequate root system to sustain the plants. It will usually take one to three years for the plants to establish. During these establishment years, little irrigation is needed during the dormant season unless the winter is exceptionally dry. A few plants, such as desert willow, do not respond well to winter irrigation, even in the establishment years. So, be certain to learn the requirements of the plants you choose.

Potting soil from compost

Can I use homemade compost as a potting soil? How do I get the insects out?

Yes, you can make your own potting soil from the compost you have made. It is a good idea to pasteurize the soil to assure that there are no diseases in the compost to injure your house plants. Properly produced compost should generate sufficient heat during composting to kill disease organisms, but the edge of the compost sometimes doesn't heat properly and may still contain some fungi or bacteria which could cause problems. You can remedy that by pasteurizing the compost yourself before using it in a potting soil mixture. This will also kill the insects you mentioned.

Pasteurize compost by heating it to a temperature of about 160 degrees Fahrenheit for 30 minutes. If you can generate this temperature for that length of time throughout the compost, you will kill most disease organisms, while allowing many beneficial fungi and bacteria to remain.

Heating the compost to this temperature may be done in the kitchen oven, but it will create a very unappetizing odor in your home. If you can, use a smaller portable oven outside, or a barbeque, or even allow sunlight to do the heating for you. Then you can avoid the unpleasant odors indoors. The compost must be moist when it is pasteurized.

To use your compost as a potting soil, you will probably want to add sharp sand, perlite, or other material to it. A few plants will do well in the compost without amendments, but a well-decomposed compost will probably become too soggy for many container plants, so the addition of materials to increase drainage will be beneficial. If you plan to add other soil and amendments to the compost to make your potting soil, it is wise to add these ingredients to the compost before pasteurization so that these components are also pasteurized.