Issue: November 3rd, 1997

Using homemade compost

I used home made compost to pot some of my houseplants, and they have either died or are looking very unhealthy. I thought compost was good. What did I do wrong?

Compost is good when properly made, but it is not recommended for use alone as a potting soil. The compost holds too much water for most plants and tends to suffocate the plant roots by not allowing enough air into the soil. If the compost has not matured sufficiently, it may also continue composting in the pot, releasing heat or substances toxic to plant roots. Of course, if the compost didn't heat sufficiently during the composting process, there may be disease organisms causing root rots.

As long as the last two conditions are not causing the problem, immature compost or diseases, addition of sand, perlite, or vermiculite can open the soil enough to promote proper drainage and aeration. The quantity of material added depends on the structure of the compost and the plants being grown. If there are undecomposed chunks of bark or shredded wood in the compost, they will facilitate drainage and aeration while continuing to compost slowly without causing problems. If the compost has been screened to remove the larger chunks, greater quantities of sand or perlite may be added to open the soil for drainage and aeration. Plants natito bog soils will need less drainage. Houseplants from the tropical rain forests need more or less aeration depending on their native growth conditions. Plants with fleshy or spongy roots will often need more drainage while those with fine, fibrous, roots will need less. Cacti and plants from desert regions will need little compost and a potting soil composed of a large percentage of sand or gravel. You can compensate for a soil that is too well drained by more frequent watering, but a soil that is too poorly drained can be a very difficult soil in which to grow plants. So if you must err, err on the side of excess drainage and aeration.

When to prune roses

Is it time to prune roses now in New Mexico?

No. You may prune them back a little and tie or stake the canes to prevent wind damage during the winter, but save the final pruning for the spring beginning about a month before your expected last frost. If you prune the roses now and the weather turns warm, the roses may begin growth which will be killed by the cold weather which follows. Roses, especially hybrid tea roses, floribunda, and other roses commonly planted, do not go dormant like deciduous trees; they are merely quiescent, waiting for appropriate weather conditions for growth.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!