During plant establishment
All newly set plants, regardless of their ultimate water requirements, must be watered regularly until they are established. This can take as little as 6–8 weeks or as long as several years. The length of time for a plant to become established is affected by:
- plant species
- the season when the plant is set out
- plant health
- root ball size — Small root balls are usually the best choice because there is a much higher proportion of feeder roots in the root ball, less chance of girdling roots, and a much better volume/surface area ratio (see the table below).
- root damage during planting — Roots are disturbed during transplanting and it takes time for the plant to replace them.
Don’t underwater
Water need is proportional to root ball volume and independent of the plant species. However, rain delivers water in proportion to root ball surface area, which is not sufficient to wet the root zone of even a small container.
| Pot size | Water need | 1″ rain | Difference |
|---|---|---|---|
| gallons | |||
| 1 | 1.0 | 0.19 | 0.81 |
| 2 | 1.8 | 0.24 | 1.56 |
| 3 | 3.1 | 0.41 | 2.69 |
| 5 | 4.6 | 0.48 | 4.12 |
| 15 | 16.0 | 1.10 | 14.90 |
| 25 | 31.0 | 1.90 | 29.10 |
Water plants individually
Uniform application of water over a bed of plants with different size root balls will not deliver the water each plant needs. It is better to water each plant separately, varying the application according to root ball size.
Established plants
Water need is species-dependent once plants are established. When landscaping, group plants by water need to facilitate efficient irrigation.
| Water Need | Irrigation |
|---|---|
| low | none |
| moderate | during dry periods |
| high | often |
During the growing season, most trees and shrubs benefit from thorough watering monthly if it has not rained. Normal lawn watering is not a substitute for thorough tree and shrub watering.
