ARS Master Rosarian
Wow, talk about a “change in the weather!” This winter has seen an additional 10” of rain in Temecula compared with last winter (December thru March). While that bodes well for water available to drive growth, we've also seen lower average high temperatures.
While last winter's highs tracked the historic average (with some days getting as warm as 84o), each month's highs this season have averaged 8o to 10o below normal. (“Normal” is usually the average for the previous 20-30 years, depending on the source.)
That means that the air and soil haven't warmed up as much as normal, so roots and new shoots are less active. Consequently, you're probably seeing slower growth. Most years by now you'd have, or be about to have your first flush of blooms (8 - 10 weeks after your winter pruning), but this year you're likely to see at least a 2-week delay.
As far as diseases are concerned, you might expect that more moisture automatically means more disease (especially fungal such as powdery mildew, downy mildew, and rust), but the lower temperatures and the cleansing action of the rain (washing off dust and spores) may be offsetting that. In the next few weeks you may begin to see some powdery mildew and rust, especially if you haven't begun a preventative spray program.
Under these wet conditions, now is the time to pay attention to the drainage of your soil. Roses like plenty of water, but they generally don't respond well to soggy soil. If you see pools of water standing in your rose beds for a few hours after a downpour, you might do well to provide a temporary path for drainage using a hoe or shovel.
Roses love food, preferably good quality food on a regular basis. Not all fertilizers include all the micro/macro nutrients needed, so read the label on the packaging. Alternating the major fertilizer with fish emulsion every two weeks will help provide some of the micro nutrients. As I always say, organics are much better for your soil and ultimately for your garden and the environment.
I'm told that sprinkling 1/2 cup of epsom salt (magnesium sulfate) around large size plants, 1/4 cup for smaller plants, once in spring and once in fall, can assist in getting new basal breaks (new canes from the bud union). I've done this many times but I'm not sure it works! However, recently I've read that epsom salt helps plants assimilate other minerals (fertilizers) in the soil. It assists in “greening” up vegetation.
For general health and aeration, the soil needs a supply of organic material such as humus incorporated into the depths. That isn't easily accomplished in established gardens, however adding 3-4” of a good composted mulch over the entire garden, leaving a 12” diameter circle open around the base of each bush will go a long way to enriching your soil overall.
Over time earthworms help transport that mulch down into the soil where the microbiology is complex and multi-tiered. Adding a handful of worm castings now is a good idea for improving the soil biome.
A healthy garden soil system is teeming with beneficial microbes that inhibit, compete with, and consume disease-causing organisms. This creates a sustainable soil "immune system." In fact, plants grown with organic fertilizers are themselves more resistant to pests and diseases. In addition, when you feed those beneficial organisms, they feed your roses. That's because they are busy breaking down organic matter and releasing mineral nutrients slowly and reliably.
I've recently learned that extra phosphate in the fertilizer that you use is most important in assisting and in creating a soil environment that aids immensely in helping plants to be resistant to pests and diseases. Phosphates help plants to develop hardier root systems and larger blooms.
Many gardeners become discouraged when they first experiment with organic treatments while still using chemical fertilizers. It is difficult, in fact, almost impossible to have it both ways. Chemical fertilizers negatively impact the soil food web by poisoning entire portions of it. The fact is, chemical fertilizers are salts!
What gardener hasn't seen what table salt does to a slug or snail? Salts absorb water and dehydrate the soil microbes which are the foundation of the soil nutrient system. Once you've used chemical fertilizers regularly you must keep adding more because the soil microbiology is weakened and unable to do its job of releasing naturally available nutrients to your plants.
Rains help to leach accumulated soil salts from the soil, provided there is sufficient drainage. Organic fertilizers and amendments (such as manure, compost, or mulch) break down slowly, generally staying where you put them, and don't contribute to groundwater pollution (as long as you prevent runoff into drains). In addition, they improve the soil food web, so in the long run you end up using less product.
Chemical fertilizers are artificial growth stimulants and, in the long run, harm your soil and pollute local waterways because as dissolved salts they quickly leach through the soil (becoming unavailable to your plants) and enter the groundwater.
How about swearing off chemical fertilizers for the rest of the year and starting to use organics? Give it a year. See if your roses don't reward you! Fish emulsion diluted in water is also a good amendment, applied either foliarly or onto the soil around each bush.
You may have had some blooms already. Prune off the spent blooms. Cut the cane back to an outward facing bud at a 3-5 leaflet leaf for new growth. Air circulation is important to help prevent fungi diseases. The small spurs growing inside the bush can easily be finger pruned to keep the center of the bush free of extraneous growth.
Giving the bush an early morning shower to rinse off the leaves may help to avoid powdery mildew. Do this early enough that the leaves will dry prior to hot sun. It is possible that with night time dew a disease called botrytis can appear as discolored spots on the blooms, especially on blooms with 40 or more petals. Remove these as soon as disease is noticed.
Even with great observations and preventive methods, fungi may become a problem and chemical treatment may be needed to keep disease at bay. Make sure to deep water. An extended slow watering is more beneficial than a frequently short application.
Now that we're no longer social distancing and masking, rose societies are returning to regular meetings and suggesting for persons with a health issue to wear a mask for their protection. San Diego Rose Society is planning an April 22 Pacific Southwest District Rose Show and Convention. For more information, go to: https://www.sandiegorosesociety.com/.
This promises to be a big show, so please make an effort to attend, to see, smell and learn about different rose varieties and find a new one for your garden!
For more ideas visit TVRS' Rose Haven garden at 30592 Jedediah Smith Road, Temecula, as well as at TemeculaValleyRoseSociety.org/index.shtml.