Your Urban Horticulture Resource



SieveTube is a web site devoted to diagnosing and solving landscape problems in the environment where people live and work. This discipline is often called Urban Horticulture, horticulture of the “built environment”. The site in not about gardening, agriculture or native environments.

SieveTubes are the part of a plant than translocates or moves sugars made using the suns energy, carbon dioxide from the air and water from the soil. SieveTubes are like the heart of a plant.

The SieveTube web site belongs to John T. Law Jr., Ph.D. The information, photos and graphics has been collected for about 30 years. Sometimes the origin of the materials is not known. If you see content that belongs to you let me know and I will take it off, or acknowledge you. (

John and Linda in SF

Dr. Law is a Plant Physiologist by training and in his approach to sustainable landscape practices and solving landscape problems.

A Plant Physiologist looks at the plant growing environment, pest pressure, and landscape design for their effect on essential plant functions such as growth, pest tolerance, photosynthesis, and respiration. Healthy, vigorous plants look better, have fewer pests, use water more efficiently and live longer.

SieveTube focuses on urban landscapes in the West, especially California. This region is distinguished by geologically young soils and irrigated landscapes. Geologically young soils are usually very fertile. Typical soil tests have very little value for Western urban landscapes, except perhaps to document visually obvious symptoms. Woody plants on established landscapes typically require no fertilizer. Weeds typically respond much better to fertilizer than the desirable landscape plants.

The mineral part of soil is sand, silt and clay. Geologically young clay is extremely reactive. This means soil with only a small amount of clay is very cohesive as it dries and the soil has a clayey character. Clayey soil can be easily molded and roots have difficulty growing into the soil.

California has high earthquake damage risk. To mitigate this risk, site development requires all the soil to be compacted. Roots grow poorly in compacted soil. Western clays and compaction result in very slow water infiltration rates. Most root growth is close to the soil surface. Irrigation design and management, and plant installation should accommodate slow infiltration rate and shallow roots. Stormwater infiltration from bioswales and detention areas is very slow.