4 Advice to Choose a ammonia sulphate for lawns

Robert Morris

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Xtreme Horticulture

Question:

 I read an article about using ammonium sulfate to keep lawns green. Can I apply this all summer long, every 8 weeks?

Answer: Yes, you can. Use a high-quality lawn fertilizer once a year as one of the applications. The best lawn fertilizers have a ratio of nitrogen to phosphorus to potassium of 3-1-2 or 4-1-2, with most nitrogen available as slow release. An example is 21-7-14. Many others are available.

The primary nutrient lawns need regularly is nitrogen. Nitrogen fertilizers keep lawns green and lush. Nitrogen is the first number on a fertilizer bag's triad of numbers.

For ammonium sulfate, this is 21-0-0. A bag of ammonium sulfate contains nitrogen, hydrogen, sulfur, and oxygen in mineral form with no fillers. Ammonium sulfate is 21% nitrogen. The usual recommendation for lawns is 1 pound of nitrogen per 1000 square feet.

This is applied using a spreader such as a drop spreader, broadcast spreader, or hose end applicator. Since ammonium sulfate is 21% nitrogen, then 5 pounds of 21-0-0 delivers about 1 pound of nitrogen.

However, I find that half to three-quarters of this rate is sufficient, especially if using a mulching mower and letting clippings fall back onto the lawn. Lawn clippings are rich in nitrogen and act like an extra fertilizer application.

In most cases, we have two types of lawns: tall fescue and Bermudagrass. Both types require a high nitrogen fertilizer about every eight weeks, but the timing differs.

A fertilizer application at Thanksgiving is vital for a dark green tall fescue lawn through winter. Bermudagrass does not need this.

To simplify, apply lawn fertilizers to tall fescue on Labor Day, Memorial Day, and Thanksgiving. For Bermudagrass, replace the Thanksgiving application with one on the Fourth of July.

There is no harm in a fourth application to tall fescue around the Fourth of July during the heat, but it is likely unnecessary. Any summer application to tall fescue should be at half the recommended rate.

Question: What causes brown spots and leaf scorch on my tomato plants? I grow about 17 different tomato plants of various varieties in containers with good potting soil and compost, and they are drip irrigated.

Answer: This time of year, brown spots can develop on tomato leaves. As the season progresses, disease issues can become inevitable. Preventing disease should be a priority for tomato plants.

It's too late this season, but some varieties are more disease-resistant than others. Research and choose varieties that are disease-resistant and produce the type of fruit you prefer.

Tomato cages are useful in supporting fruit off the ground, reducing rot risk. However, cages can crowd the plant's interior, preventing enough sunlight and air circulation, promoting disease. Trim older leaves near the center to improve air circulation and reduce disease issues.

Drip irrigation helps by watering at the plant's base, unlike overhead watering, which keeps the plant's center wet and encourages disease. Avoid overhead watering; it can spread disease from leaf to leaf.

Feed the plants regularly, continuing monthly feedings when fruit has set to replace nutrients taken from the soil.

At the first sign of disease, take action. Fungicide applications may be necessary. Choose a fungicide effective against common tomato diseases like early blight. Fungicides are generally preventive, not curative, once the disease has started.

Question: My passionfruit tree on the north side of the house flowers but the flowers fall off after self-pollination. What can I do?

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Answer: Passionfruit is a tropical or semi-tropical vine, not a tree, and requires a trellis for support. In desert conditions, it requires more care and may freeze back to the ground annually. If roots are protected, it will regrow in the spring.

Planting on the north side of a building is okay, but the east side is better for morning light and afternoon shade. Add compost to the soil at planting and annually.

Wood chip mulch helps retain moisture and keep roots cool. Drip irrigation works, but the plant might perform better if rooted in a large basin that fills with water.

Different varieties perform better in desert conditions. Varieties like Frederick, Incense, and Blue Crown have shown success in Phoenix. More information is available at phoenixtropicals.com.

Remember, Phoenix has milder winters and better soil than our area, requiring better winter protection and soil improvements.

Passionfruit is a heavy feeder, needing frequent fertilization. It sets fruit more easily in late spring and early summer but struggles in extreme heat. Hand pollination might be necessary if fruit does not set.

Question: My tomato plants, transplanted outside on April 3, have holes in the leaves but no visible insects. What could be the cause? It only affects a few upper leaves.

Answer: Having closely examined the pictures, it does not appear to be a disease problem. The ragged edges of the holes do not suggest insect damage, likely indicating wind damage. I wouldn’t worry about it.

You transplanted them a bit late. Transplants should be planted by mid-March.

Avoid overhead watering; water at the base. Once fruit appears, apply light fertilizers monthly.

Remove the oldest, shaded leaves from the plant's center to improve air circulation, reducing disease risk. Watch for whiteflies and spider mites as temperatures rise.

Robert Morris is a consultant, horticulture specialist, and professor emeritus in horticulture with the University of Nevada Cooperative Extension (UNCE). His blog is Xtremehorticulture of the Desert Blog. He can be reached on Skype at RLLMorris, cell and VOIP at 702-630-5173, and LinkedIn at Robert L Morris. Email questions to morrisr@unce.unr.edu.

Types of Nitrogen Fertilizer

Nitrogen fertilizers are classified by the rate of nitrogen release. The two primary types are water-soluble nitrogen and slow-release nitrogen.

Water-soluble nitrogen becomes available immediately after being watered in, rapidly greening the lawn and stimulating growth. However, its effect is short-lived, requiring more frequent, lower rate applications to maintain nitrogen supply. Examples include ammonium nitrate, urea, ammonium phosphate, and ammonium sulfate.

These fertilizers have salt-like characteristics that can cause desiccation injury (burning) by drawing water out of leaf tissue. This is common when ammonium sulfate or urea are applied to moist turf but not watered in immediately. Avoid foliar burn by thoroughly irrigating turf after application to wash off granules or dissolve them completely.

Slow-release nitrogen fertilizers dissolve slower than soluble fertilizers, providing nitrogen over time. They cause less initial color and growth response but have a lower burn potential. Because of this, they are more expensive than soluble fertilizers.

Common slow-release nitrogen fertilizers include methylene ureas (Nitroform and Nutralene), sulfur-coated urea (SCU), polymer-coated urea (PCU), polymer-coated SCU (PCSCU), isobutylidenediurea (IBDU), and natural organic sources such as activated sewage sludge and mixtures of feather meal, dried poultry waste, and dried blood.

Synthetic methylene ureas release nitrogen when soil microorganisms break them down, making them effective in warm weather but less so in cooler times.

SCU fertilizers rely on water permeating the sulfur shell to dissolve the urea. They release nitrogen faster at higher temperatures, with common SCU materials releasing nitrogen faster than other slow-release sources.

PCU and PCSCU fertilizers depend on water movement through a polymer shell to dissolve the urea, which then diffuses into the soil where plant roots absorb nitrogen. Their nitrogen release is faster in warm weather and slows down significantly in colder temperatures.

IBDU relies primarily on water hydrolysis to release nitrogen and performs effectively year-round but shows weaker responses on initial applications. Over time, it is highly effective.

Protein-based natural products release nitrogen when broken down by soil microorganisms, being highly temperature-dependent and faster in summer and fall. Their effects are similar to methylene ureas, PCU, PCSCU, and IBDU. Natural organic materials are well-regarded and commonly used in Oregon.

Commercial fertilizers often combine soluble and slow-release nitrogen sources to provide both an immediate and lasting response, lower burn risk, and intermediate cost.

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