Care of new plantings

A newly transplanted woody ornamental typically requires up to ten years to fully re-establish its root systems. Generally, the older & larger the transplanted plant, the longer the re-establishment period. During that process, whenever the output of water through transpiration exceeds input via root absorption, the leaves will be the first to be compromised. The more severe the water’s imbalance, the more damage to the foliage or more severe the dieback. First the oldest leaves turn yellow and are cast off, then the tiniest new growth dies, usually turning greenish brown, then younger and younger leaves drop, followed by peripheral necrosis and leaf cast. Finally twigs and branches die, generally from the top down, and if the imbalance is severe, the whole plant dies.

Coniferous evergreens are the most unforgiving. Once significant wilt occurs, indicated by a change in the needles’ luster, temperature and color, it is probably already too late to save the plant. Applying any amount of water is usually a waste of time. They seem to die over-night.

When herbaceous or deciduous plants lack water, they `wilt'. Wilting does not necessarily produce visual signs. It may produce a color or luster change in the foliage. Some plants like, impatiens and coleus, visually wilt whereas other do not. Yellowing of the leaves is only one of the many visual signs of imbalance that a plant is attempting to correct. By wilting, a plant is trying to shut down the evaporation from its leaves, thereby conserving moisture. Generally speaking, wilt occurs approximately a week before the oldest leaves turn yellow. Watering a plant once the leaves begin to turn yellow helps prevent additional leaves from turning yellow a week later and beyond. Those that started the wilt process just minutes before watering will continue to turn yellow, as the process cannot be reversed. People often fail to recognize for this delayed effect and end up over-watering the plant, believing more water must be the answer. The philosophical error is further reinforced as the plant stops loosing leaves in about a week. I don't believe you or anyone else can reverse cellular death represented by yellow leaves. If you can, you are in the wrong occupation.

Over-watering produces a different set of symptoms that I will describe in a future issue. 

In Spring, with its cooler temperatures and generally abundant moisture, a plant puts out nice healthy growth as water needs and availability are nicely balanced. Once the temperatures begin to heat up, things may go out of balance. If drought and heat are combined for too long, death commonly results. If you were to look closely at some woody ornamentals, you will notice that some have finished growing for the season once the heat and drought begins. When the Spring flush of growth is over, the plant settles down to producing seeds, fruits, store nutrients, continue developing wood, roots, etc. Acer -- Maple, Quercus ­ Oak, Tilia ­ Linden and Cercidiphyllum ­ Katsura, Pinus ­ Pines, and Picea ­ Spruce are some examples that commonly produce a flush of growth in the Spring and are pretty much finished growing by July.

Other woody ornamentals continue to grow during the entire season. Salix ­ Willow, Morus ­ Mulberry, Rosa ­ Roses, Malus ­ Crabapple, Gleditsia ­ Honey Locust, Juniperus ­ Juniper, Taxus, -- Yews and many others continue growth until the first hard frost. On some plants, very late growth simply doesn’t have enough time to properly harden off before Winter and tip die-back occurs. We tolerate this on roses but not on Junipers. Therefore, those with pronounced tip die back are unwanted in the landscape even though some may be very worthy garden plants.

I have come up with a formula on how to calculate water requirements on any plant, especially a newly installed one.

The following information will need to be gathered for the following watering formula.

(((((Ev2 x S)/1000)/Tcm) + ((Wv x Sm%)/1000)/T°C)+((Wv x ºDOPE)) + (((Bv x Po% + Pr)2 x Rt ) - Nut + M) /V )/10000)/10 = Dah

Ev2       Transpiration surface of the entire plant. This is the total measured surface area of all living leaves in square centimeters

Tcm      The thickness in the leaf’s upper cuticle in millimeters.

S          Stomatal number per square centimeter

Wv       The velocity of the wind at the foliage level as an average of kilometers per hour for the previous 2 hours.

Sm%     The hours of Sunlight per day directly falling on the leaves as a percentage of total leaf surface in square centimeters

T°C      The average centigrade temperature during the daylight hours only

DOPE   Hours of Daylight Over the Plant’s Environment takes into account the effect of light when direct sunlight is not falling on the plant.

Bv        The volume in cubic centimeters of soil in the original root ball. On an existing plant, multiply the radius of the crown by 5, times a  depth of .5 meters for woody plants. For herbaceous perennials, multiply the radius of the crown by 2, time a depth of .3 meters.

Po%      The percent of porosity of the original root ball soil. On an existing plant use the existing soil’s porosity.

Pr         The porosity of the soil in which the plant is being installed or the existing soil’s porosity.

Rt         The medium’s moisture retention in percent of total weight in the original root ball. On an existing plant use the existing soil.

Nut       The total available soluble salts in ohms/centimeter squared.

M         The depth of the organic mulch that is remaining on the soil within 1 meter of the plant’s center.

V          The volume of water flow, from the watering device, in liters per minute.

Dah   Equals the number of minutes to water the plant per week. If the total number is 30 to 59.9, divide by 2 and water every 4 days for that period of time. If the number is 60 to 119.9, divide by 3 and water every 3 days for that period of time. If the number is 120 to 179.9, divide by 4 and water that period of time every other day. If the number is over 180, then divide by 7 and water every day for that period of time. Tee Hee

This should once and for all answer the question on how much and how often to water a plant. On the other hand, you could feel the plant’s leaves and stick you finger in the soil to determine if it needs water. Moisture meters are available at most garden supply stores to help determine the soil’s moisture content if you don’t want to get soil under you nails.

originally published 2002 V16 #2

Offices: 5434 Dahlen Drive, Madison, WI 53705 • (608) 233-4215 • Operations: 3290 Elvehjem Road, McFarland, WI 53558