Summer Days, Summer Roses, Summer Care

by Julie A. Matlin, Master Rosarian, Butte Rose Society

This is a 2020 AOM winner

“Summertime, summertime; sum, sum, summertime”. Remember that song? That was an anthem for “freedom” for many kids, unless you had to go to summer school. For most California kids it also meant soaring temps and finding ways to keep cool! The years have passed here, but our summers are still very hot! We’ve already seen local temps climb over 100°, then plummet 20° into what many of us locals remember as the “thunder and lightning” summers of Chico in the late 60’s through the 70’s. ABOVE: Nitrogen Fixation, photo by Permaculture Magazine.

For many plants, but roses especially, our summer heat and fluctuating temps equals stressed growing conditions that, when combined with a lack of consistent watering, nutrients or healthy soil and mulching, can easily lead to a reduction in flower production, plant vigor, soil health and in extreme instances, shrub death. Roses growing in our mountain areas and places that receive little or no water go into dormancy just to survive.

Just the look of our roses during the summer months can alert us to rose health: too little or too much water; nutritional issues; soil fertility problems; shrub diseases; insect and rodent damage; bush injury. As a CR, when asked about checking rose health, I answer: get up close and personal with your roses and the soil they live in during these summer months. The number one question about rose care I’m always asked during this time of year concerns plant nutrition, and the “why, how and when” of nitrogen.

Nitrogen is a magical element in itself - “born of the stars” - and found in all living things. All plants and animals contain organic materials that contain nitrogen, and nitrogen is stored in living and dead organic matter!

Fun Fact:

Did you know that all nitrogen found both on and in the earth originally came from our atmosphere? Large amounts of nitrogen enter the soil in rainfall and through the effects of lightning. It’s estimated that about 140 million metric tons are added to the ecosystem yearly through fixation (the way nitrogen stored in the soil is changed or fixed by soil organisms).

Many gardeners don’t realize that California soils are naturally low in nitrogen, and that for optimal plant growth, nitrogen must be included in any rose feeding program. The “why” is straightforward: roses require nitrogen for basic biological processes, and therefore soil health is important. In general, the first sign of nitrogen deficiency is a yellowing of mature leaves, and sometimes young leaves, depending on the deficiency. The “how” of nitrogen is complex; embodied in a process called the nitrogen cycle and essential to all living things. The “when” of nitrogen depends on whether commercial rose fertilizers are preferred to using organic fertilizers. No matter the type of bagged inorganic rose fertilizer used, it is important to feed roses regularly during the growing season for optimal performance, but especially during summer months, for happy, healthy shrubs. Feeding regularly depends specifically on what the fertilizer label says. Not all fertilizers are the same, so always follow the directions exactly!

Roses cannot take up nitrogen directly. Its compounds must be broken down into nitrates through a complex process called nitrification. The final result: rose roots are able to absorb the nitrates that have been dissolved in soil water, which can then be transferred into the rose roots in solution. This process equals strong canes, green leaves, good bloom and happy, healthy roses. As a gardener, “soil health” is my mantra and I can't even guess at the number of bags of rotted chicken manure I’ve purchased just this year as the caretaker of five gardens. Although the nitrogen amounts vary in chicken manure, the way in which it improves soil quality and tilth, as well as providing nutrients for plant growth, is unbeatable! I can use manure all year round. I put it down in December, let the rain do its job, and the soil organisms will begin absorbing all that organic goodness when the sun really begins to shine again. Follow bag application instructions carefully, although I toss about 1 ½ shovelfuls around the diameter or drip line area around each rose. One bag will feed/compost/mulch approximately five large roses, and last for three months.

Choosing a rose fertilizer can be confusing, but the one fact to remember is that roses are “foodies” that will eat up any and all food given to them! When shopping for the “right” rose food, keep in mind that just because the bag/box says “rose food” doesn’t mean it’s just for roses! Ask yourself: are you looking for bloom, roots, leaves, general shrub health or all? The most common nutritional problems in roses in California are generally related not only to nitrogen deficiency, but also to phosphorus, potassium, zinc and iron deficiencies. The first three nutrients are the primary nutrients found in all rose fertilizers, whether dry (granular), liquid (soluble powder) or slow release. These primary ingredients are known as N (Nitrogen), P (Phosphorus) and K (Potassium).

N: Nitrogen is always the first letter listed and the most important in the spring, as it promotes green growth and strong, healthy rose shrubs. Nitrogen is the backbone of DNA. It is important in photosynthesis and bush metabolism, and essential for many growth and developmental processes.

P: Phosphorus, the second letter listed is important for rose energy systems as it stimulates early growth and root formation. It also plays an important function is photosynthesis. Phosphorus is instrumental in flower development. Many rosarians who are diehard exhibitors look for the highest “P” nutrient available to get those big blooms for show!

K: Potassium, the third letter listed, is not needed in most gardens because California soils naturally contain this element. However, potassium is important in rose root system development, and also influences rose bloom quality. Most rose fertilizers contain enough potassium to keep root systems happy. But if you think you’re not getting enough, get your soil tested and know you can always apply 0-0-10!

Whether you buy rose fertilizer in the types available: liquid, pellets, granular, tablets or stakes, know that nitrogen is always the first letter listed on the bag. Nitrogen is the most important nutrient needed by roses in spring, as it promotes green growth. Time release for roses can be as high as 19-6-12. By law, the guaranteed content of the fertilizer, given as a percentage of each plant nutrient supplied, must be listed on the bag. Think 100% - so 37% of the bag is actually fertilizer, and the rest are fillers. If micronutrients are included, they also must be listed by percentage.

Because organic matter processed through one part of the nitrogen cycle called mineralization (this occurs when organic matter is decomposed by organisms in the soil’s top layers and modifies existing nitrogen), is known to improve soil fertility, it is often added to soils in large amounts. However, adding organic matter to garden soils doesn’t necessarily improve soil fertility immediately. Further, whether a material is considered a soil amendment or a fertilizer is usually determined by its effect on plant growth. Amendments affect plant growth indirectly by improving the soil's physical condition like tilth, structure and water absorption, while fertilizers affect plant growth directly by improving the supply of available nutrients in the soil. Manure can be both: supply readily available nutrients and also supply lots of organic matter to the soil.

Even when our local temps stay high for weeks, garden soil in good physical condition (good tilth) can provide and hold adequate amounts of water, nutrients and air to plant roots as long as you, the rosarian, pay attention and plan for summer weather. If you use lots of manure to feed and compost roses like I do, remember that it’s impossible to create a permanent build up of manure/organic matter in the soil because organic matter decomposes fast and soil microorganisms gobble it up. It takes about three months for one bag of manure to dissolve into the soil.

Can you OD your roses with too much nitrogen? Yep! Nitrogen toxicity can cause excessive vegetative growth. It can also cause roses not to give much bloom because all the shrub’s energy is going into pushing growth. This can result in stunted growth and weird dark green foliage. In some Old Garden Roses and some English (DA) roses, excessive nitrogen causes “vegetative” centers to form, which actually is quite curious if you’ve never seen one. Of course the bottom line is to really pay attention to your roses during the summer months, and always follow the directions given on bags of commercial rose fertilizers.