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Irrigation for Plant Establishment

Newly planted plants of any size must be treated differently than plants that have been growing in a landscape and have fully extended their roots out into the native soil. They must be watered more frequently and checked on more often. Importantly, after California native or waterwise plants become “established,” they must then begin to be watered less frequently, allowing the soil to dry significantly between deep and infrequent soakings in order to maintain the health of most of these species.

When should plants be considered “established”?

Established plants have been growing well in the ground, usually for at least one year, sometimes longer, but generally no more than two years. They have not yet reached full size, but have grown significantly. Before this, even low water demanding or “drought tolerant” plant species are not yet adapted to the infrequent waterings we recommend for established plants.

General watering needs during the establishment period

During this establishment phase, most plants, even low-water use and native plants, will benefit from a deep watering once per week, applying 1” of water each time. Establishing plants that are being hand watered should receive 3-5 gallons of water per plant once per week. Your goal is to thoroughly soak both the existing root area of the plant plus the surrounding soil to encourage the roots of the plant to spread wide and deep, necessary for the plant to become “established.” If hand watering, one simple way to achieve this is to fill “watering rings” made of a soil mound encircling each plant with two can-fulls of a two-gallon watering can, easy to order online.

Watering for plant establishment

Every site is different, but in general, most waterwise plants, if well matched for the space they are planted into, will establish well using the following watering guidelines for the first year or so they are in the ground.

When you plant: water, water, water! It is hard to water too much immediately after planting! You want to ensure that the root ball and the soil all around is saturated down to at least 1.5’. This may require building a soil “watering ring” and will require applying water to each plant multiple times with a hose. Anticipate filling watering rings at least three times immediately after planting.

Individual one gallon plants should receive a total of at least 5 gallons of water and up to 10 gallons of water to ensure this thorough soak.

Drip or spray irrigation systems should be run for their normal run time to provide 1” of water (PROVIDE LINK TO PART IN MAIN INFO PAGE ABOUT CALCULATING RUN TIME), then a hole should be dug to check how deeply the moisture penetrated. If the soil is extremely dry, the irrigation may have penetrated less deeply than may happen going forward. Dig in a few spots and check how deep the moisture penetrated. While it may not be practical to dig multiple holes 18” deep, you will want to be sure to dig to at least 12” down and check to verify that the soil became quite wet to that level and looks to have penetrated deeper. This may require running the system multiple times in a row immediately after planting, even if this is not required for normal waterings going forward.

Establishment period (appx. one year, possibly longer): In general, during the warm season, expect to water plants once per week-ish during establishment. When you water, apply about 1” of water to the landscape area. Some plantings do well with less, so if things seem to stay too wet, you can experiment. With providing less water or watering less often. You will likely need to provide an absolute minimum of 0.5” of water every week or so during establishment. If it rains sufficiently, you can skip watering.

How to check

In the weeks following planting, check both the surrounding soil AND the nursery soil root ball of the plant. If the root ball seems dry, you may need to water even if the surrounding soil still has moisture because the roots may not have grown out into that soil yet.

Plants installed in late spring or summer may need water more often than once per week to avoid drying out and damaging the plant. On most sites, it is not likely to ever need to exceed watering newly installed one-gallon plants more than twice per week.

It is always easier to be successful installing plants in the fall or winter or early spring if necessary. Plants planted in late spring or summer must be monitored carefully to avoid either over or underwatering. This is an important enough issue that it is worth planning when your landscape will be planted to be sure it can happen in the ideal time of year for planting.

Following planting

As mentioned above, in the weeks following planting, it is recommended to observe both the natural soil in the landscapes AND the nursery soil root ball of the plant to the best of your ability.

If the root ball seems dry, you may need to water even if the surrounding soil still has moisture as the roots may not yet have grown out into that soil.

In most cases, we do not recommend using soil moisture meters to check soil moisture due to inconsistent results across different mineral soil types. However, they may be useful for testing moisture directly into the nursery pot root ball where digging would be damaging to the plants.

High quality moisture meters that can be calibrated (e.g. Reotemp brand or
similar) may be helpful if you suspect that although the surrounding soil appears
moist, the root ball may be beginning to dry out. This situation is more likely to be
a potential issue with warm season planting.

Refining how often to water during establishment

Check the soil in the general zone of the planting before watering again and dig down a couple inches or so. If there is still significant moisture within the top two inches, and the root balls do not seem dry, you can wait a bit longer before watering. Depending on the weather in the fall and spring, if plants have already started to root into the soil around them (which you can normally determine by the presence of some significant branch or stem growth), you might not need to water quite as often as every 7 days, potentially going 10-14 days in between waterings if the plants and soil look good.

Once plants have at least tripled in size from planting and it has been a year or more, it is time to begin to water less frequently to both save water and better support the long-term health of your plants.

What to do once plants seem established

While keeping an eye on how your plants respond to be sure you are not overly stressing them, begin to move toward our recommended ongoing irrigation schedule for established plants for the plant species you have in that area of the landscape.

At this point you have two options. When they believe their plants have reached “establishment,” some people will jump directly to our recommended “established” watering interval. If plants react well, they will then keep this as the ongoing irrigation frequency, while making small tweaks as observations dictate (LINK TO RELEVANT PART OF OTHER ARTICLE?)

Another option for those growing native plants that will eventually only be watered every three to four weeks or less is to move into a “transition year” where plants are watered less than once per week, but still more frequently than the final irrigation schedule. Often this frequency might be every other week. In certain instances, this may help allow plants to begin to experience the necessary longer dry period in between waterings while still providing a bit more water to plants that may not yet be completely established. If following this approach, be sure to watch for signs of both overwatering and underwatering over the next year.

Overwatering and underwatering can both look like a plant wilting, so if you see what looks like wilting leaves, first check the soil to see if it seems overly wet or overly dry before making any watering adjustments.

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