It’s a good time now to give your roses about two cups per plant of alfalfa either pellets (buy at a feed store) or meal (sold at some nurseries). Alfalfa is a great soil amendment and provides a bit of nutrition, it contains a growth hormone triacontanol which is said to be a plant growth regulator. Some rosarians are skeptical about the effects of the hormone, but I will say that I see a distinct improvement to soil structure in rose plantings where it has been used for a few years.
Many of our exhibitors add poultry manure at the same time as alfalfa following label directions for application rate. Lightly scratch both into the soil. Make sure to wear gloves when working with manure and have your tetanus shot current. Avoid fresh poultry manure since it may burn feeder roots. Use only aged manure. I make my own compost and will add that sometimes to stretch the poultry manure.
Many rosarians add a two-inch layer of compost twice a year to suppress weeds and help retain moisture. In the fall this top dressing can be turned into the soil where it helps aerate, hold water, and nourish soil.
The middle of March is a good time for an application of organic fertilizer, then another application in May after first bloom, and then another lighter application in July. Finally, the last feeding is in September to allow time for growth to harden off before the dormant season.
I had used an organic called Perfect Blend and applied their 4-4-2 formula which worked well for me. The distributor I got it from no longer carries it, so I have switched to a slow-release fertilizer called Apex which was recommended by rose grower and plantsman Tom Liggett. Apex, a chemical fertilizer, is similar to Osmocote in that the slow steady feeding prevents growth spikes which may lead to insect and disease problems. With a slow-release food like Apex, which feeds for eight or nine months, you can periodically augment your program with a light application of a bloom food or low nitrogen food like fish emulsion. Fish emulsion is a 5-1-1 formula. Fish emulsion is mixed with water. Apply it at the rate indicated on the label. A nurseryman I know, who has been in the business 50 plus years, says you can’t burn with fish. Fish emulsion helps build soil tilth and provides a slight acidic reaction which roses enjoy since they prefer a pH of 6-6.5.
There are many other organic and synthetic formulas available through nurseries and mail order houses. Always apply any fertilizer to a damp soil and in the case of dry fertilizers be sure to water well after applying.
Chemical fertilizers are an option still used by many rose growers often due to the fact that usually they are less expensive than organics. Many people have stopped using high nitrogen synthetics since they do nothing to improve soil health and can cause salt to build up over time in soil. High nitrogen synthetics cause such rapid growth that roses form elongated cells with weak thin walls making them easy targets for insects like aphids and others. This vulnerable and succulent growth is also attractive to foliar diseases.
Osmocote or Apex can be pricey, but some formulations can last an entire season of time release feeding. So, you spend a lot less time feeding.
The results I got my first year were nothing short of spectacular. A climber called ‘Darlows Enigma’, which had sat in a 15-gallon pot for seven or eight years with Max Sea 16-16-16 as the primary food and just never did much growing, pushed out three or four new basal canes and these grew to eight feet or more by the end of the season. This rose was covered entirely by a profusion of flowers . It had previously been a sparse bloomer. ‘Hot Cocoa’, which in the previous year had smallish leaves and meager blooms, put on good size foliage with plenty of blooms including a large candelabra for the first time.
I had a client with a big rose garden on the slopes of Mount Tamalpais who called asking if I could get her ‘Royal Sunset’ climbers in shape for a wedding at her estate in early July which was about six weeks off.
The first thing was deadheading and some light cutting back. After that, I used a Ross Root Feeder since the roses were in a big cement patio with cutouts in the concrete that were no more than 10 or 11 inches across. The root feeder seemed to be the only way to make sure food was delivered to the root zone and could saturate the root zone. The formula I used was a 15-25-10.
I had the client instruct her gardener to apply Max Sea Bloom Formula 3-20-20 several weeks after the Ross food. I talked with her, as our Marin Rose Society pruning team did dormant pruning in February, and she said the roses were incredible for the wedding.
Climbers, when mature, are two to three times bigger than shrub roses so they are given two to three times the amount of food. When using a dry food apply double rate and a bit more often than for shrubs. If using a liquid, use enough to saturate the soil very well.
Miniatures are generally hardier to heat and cold than their big sisters, but very sensitive to fertilizers. Always feed them half strength. Minis love fish emulsion and organics. Water minis in pots well before feeding, remove saucer if used and allow them to drain completely and not sitting in standing water.
We have all seen the chemical rose food that also contains systemic insecticides and systemic fungicide. It is tempting to use this product when trying to control a pest like rose curculio aka ‘rose weevil’ or bristly rose slug. However, I can recall that as a student at the College of Marin landscape program in the late 70’s we were cautioned that using this product more than once per year caused damage to the tiny feeder roots of roses. It seemed to make the most sense to use it as the first feeding of the season, since that is usually when the possibility of rain can make it difficult to apply spray controls.
Epsom salts are another fertilizer related topic that many rose lovers have definite opinions on. Epsom salt is the micronutrient magnesium sulfate. Some good things Epsom salt does for roses includes the following claims – more basal canes, more brilliant colors, larger blooms, more blooms, greener foliage, a more vigorous plant. Epsom salt is said to have no impact on pH so that is not a concern. Epsom salt can be applied as a spray, providing care is taken to avoid burning leaves. It should not be applied in direct sunlight, probably best in early evening or late afternoon. It can also be added to soil as per directions.
In California, soils contain sufficient magnesium, so to be safe it may be best to limit use to container plants. Former ARS President, Jolene Adams, spoke to our membership and said that Epsom salts should not be used on roses in our state.
By Richard Holtz, Consulting Rosarian
Edited for the website by Nanette Londeree, December 2020