The heady aroma of apple blossoms and citrus blooms have filled our backyards recently. As hobby fruit growers, we are anticipating baskets of lemons, oranges, apples, figs, peaches, persimmons and more. This article will address watering and fertilizing fruit trees at the best time and in the appropriate amounts. This will help them achieve their purpose and you to gain a bountiful harvest.
Trees in suburban environments are often under high stress conditions due to low moisture availability, soil compaction, physical damage, nearby construction, and competition from turf and nearby trees and shrubs. Fertilizer applications may reduce, but cannot eliminate, environmental stresses such as these. Additionally, not all fruit trees need fertilizer every year and they don’t need it in the same amounts. Too much fertilizer means lots of leaves and shoots, but not a lot of fruit. Luckily, fruit trees are pretty good at telling us what they need.
There are several ways to determine if your tree needs fertilization. The best indicator is a soil test. Ideally, a soil sample should be taken before trees are planted. Additional samples can be taken every 3 to 5 years thereafter to determine whether any nutrients are lacking. A soil test kit may be obtained from your county AgriLife Extension office.
In the absence of a soil test, the best indicator of the need for additional fertilization of established stone and pome trees is shoot growth. Begin your assessment of a tree by locating last year’s growth rings. The growth ring is the point on the branch where the tree started growing the previous year.
Measure from the growth ring all the way out to the end of the branch. Repeat these measurements at several spots around the tree, and average them as the previous year’s “annual growth” of the tree. If the tree was pruned heavily the prior year, don’t fertilize this year.
Use this chart to evaluate your tree’s annual growth. If the tree’s number is at the low end of growth, then you should fertilize the tree this year.3
Foliage color is another indicator of the need for fertilization. Yellow or “off-color” leaves may indicate the need for fertilization as these symptoms generally occur on trees which are not taking up enough of one or more required nutrient. Always remember, however, that seemingly “off-color” leaves can be normal for certain plants at certain times of year.
Citrus that are lush and green do not need fertilization. Too much fertilizer can actually retard fruit production. If the canopy is sparse and “off-color” you will improve productivity with the fertilizer application described this article.
A final indicator of the need for fertilization is the history of the yard. Trees in yards that are fertilized for turf on a regular basis rarely need to have supplemental fertilizer applied. Supplemental fertilizer should only be considered if shoot growth is less than 2 inches, or if a soil test reveals a specific nutrient deficiency.
If the only indicator of the need for fertilization is slow shoot growth, then a high nitrogen fertilizer should be applied to the tree. If, however, the leaves of the tree are yellowing, or there is some other indication of a nutrient deficiency, then it is appropriate to take a soil sample from around the root zone of the tree and have a soil analysis performed.1
The soil must provide 13 nutrient elements essential to all plant growth. Texas Gulf Coast soils generally are quite fertile and contain more than adequate quantities of all essential elements except nitrogen. The other elements rarely need to be applied to mature fruit trees. However, the exceptions are important.
Clay soils usually contain plenty of iron, but citrus trees may exhibit iron deficiency in the early spring. Usually, the deficiency clears up as the soil warms up. If it does not, soil application of iron chelates is necessary. Where iron deficiency does occur, do not use fertilizers which contain phosphorous because high phosphorous aggravates iron and zinc deficiency in high pH (alkaline) soils. Red, sandy soils may need supplemental potassium and sandy soils in general may need additional zinc.
Mature, bearing trees should receive enough nitrogen to provide for good but not excessive growth. If the percentage of nitrogen in the fertilizer is less than 15 percent, apply about 1 pound per inch of trunk diameter per year. If the percentage is above 20, use 0.75 pound or less per inch of trunk diameter per year. One pound of dry fertilizer is approximately 2 cups.
The fertilizer may be applied at one time for the year, usually in February, or it may be split into two or three applications. Your AgriLife Extension office recommends using the dates of Valentine’s Day, Mother’s Day and Father’s Day to remember the best time for fertilizing in the Texas Gulf Coast area. Remember to divide the original amount into three equal applications.
The most expedient application is to spread the fertilizer uniformly on the soil surface under the tree canopy and slightly beyond and water it in thoroughly. It is not necessary to drill holes in the soil for fertilizer as a thorough watering will carry surface-applied fertilizer down to the roots. 4
Remember that plant nutrition is a balancing act and that too much fertilizer, as well as too little, can negatively affect the growth and production of your trees. The correct amount will keep trees healthy, enhance landscape beauty and ensure a delicious harvest.1
According to Julian Sauls, Texas A&M Professor and Extension Horticulturist, irrigation in the home landscape, probably the most expensive and time-consuming production practice, is poorly understood. Water commonly is applied too frequently and in inadequate amounts, resulting in inefficiency, waste and less than optimum growth and production.
Newly planted trees require a gallon of water (approximately 6 inches5) every 7 days or so during a normal growing season. This water amount will naturally increase as the tree puts on new leaves and moves into summer, decreasing again in the fall. This may require hand watering since most irrigation systems are not run long enough to be sufficient. If you are experiencing rainfall in that time, you should not need to provide additional water, but use your best judgment and a rain gauge since water availability and soil drainage may vary greatly from one location to the next.
Although newly planted trees need to be hand watered to insure proper irrigation, Dr. Sauls suggests a good irrigation schedule for established trees is simple to develop. You need a couple of pet food or tuna fish cans about 2 inches tall. Set them up somewhere in the middle of the yard so they will be exposed to wind, rain, and sun, covering with wire mesh to prevent birds from drinking from them. Fill with water immediately after a thorough irrigation or good soaking rain.
Assume the cans will hold 2 inches of water. From mid-April through mid-September, irrigate with 1 1/2 inches of water when the cans are completely dry, then refill the cans and wait for the water to evaporate again. The rest of the year, irrigate with 1 inch of water when the cans are dry. The difference is that growth in the cooler months uses only about half as much water as evaporates, while growth in the warmer months uses about three-fourths as much water as evaporates.
Sandy soils usually can absorb water as fast as you can apply it, but water penetrates very slowly in clay soils. Adjust the application rate to prevent water runoff. 4
As a tree grows older, its roots become established, and the need for watering moves away from survival and growth to fruit size and quality. Timely watering, especially during droughts, will make a big difference. Always pay attention to that period after seasonal rains end and you suddenly realize it hasn’t rained in weeks.
Water-related stress occurs at both ends of the spectrum. Overwatering can cause yellowed leaves and defoliation. Under watering can cause curled leaves and defoliation. Try to keep things at a happy medium: your trees will tell you what they need if they are unhappy! 2
These springtime garden tasks will get your garden in shape for the long growing season ahead. Should you have any questions concerning your trees do call the Master Gardener Hotline, 281-341-7068 or email us at FortBendmg@ag.tamu.edu. Photos are always appreciated and makes diagnosis easier.
1 Tree Fertilization: A guide for fertilizing new and established trees in the landscape
Jeff Gillman and Carl Rosen
Modified from original publication by Bert Swanson
2 Fruit Tree Care: Watering & Fertilizing
3When & How to Fertilizer Your Fruit Trees, GrowOrganic.com
4 Fruit & Nut Resources, Citrus
Julian W. Sauls, Professor and Extension Horticulturist, Texas Agrilife Extension
5Arizona Cooperative Extension, Converting from Gallons – to Inches – To Runtime, Edward C Martin and Armando Barreto