by Nanette Londeree, Master Rosarian
After one of the wettest winter and spring seasons on record, why in the world would one even think about drought? Isn’t that when there is a water supply shortage? With our reservoirs still near their capacity, it can’t be too much a problem, can it? Well, it really depends on what kind of drought we’re talking about. There’s a meteorological drought, the kind where you don’t get enough normal precipitation over a period of time. An agricultural drought occurs after a meteorological drought and is the lack of adequate soil moisture needed for a certain crop to grow and thrive during a particular time. You may experience a socioeconomic drought, when the physical water supplies are so low that they negatively affect the community where the drought is occurring. Or a hydrological drought – when precipitation has been reduced for an extended period of time, and water supplies found in streams, lakes, rivers, and reservoirs are deficient. From a plants perspective, a drought is simply when it doesn’t get enough water to grow.
Nature produces all types of plants with varying water needs; there are drought tolerators – plants that are able to survive and even thrive with minimal water like many of our California natives. There are drought avoiders – plants that have very deep taproots that allow them to grow well during limited rainfall. Many species roses fall into this category. Our garden roses are drought evaders – they avoid water stress by dropping their leaves, producing small blooms, or becoming virtually dormant. In this stressed state, they become targets for all kinds of pests and diseases. Roses are generally drought wimps, they like water and lots of it. The key is to make sure they get the right amount of water when they need it.
You already know that, like most living things, roses are made up primarily of water, so in order to grow and flourish, they need a steady supply of this vital element. There’s lots of information available about how to water, when to water, maintaining moisture in the soil, all the available systems and tools for watering, so no need to discuss that further here. But are you sure your plants are getting enough? You water your potted roses religiously and have all the others on an automated system. No restrictions from your water provider, so you needn’t worry about drought. But think again – have you ever had a rose that looked great during the spring rains, only to sulk for the rest of the season? It didn’t wilt, it just didn’t do much of anything. Or a rose that put out some really stingy little flowers, and was a magnet for spider mites? Time to look a bit closer to be assured that your roses are not inadvertently suffering from drought.
Consider some examples; a well established, mature ‘Cathedral’ floribunda put on a spectacular display in the spring. Then along came late rains, a bit of blackspot, leaf drop and warmer temperatures. Other roses in the area bounced back from the disease – but not the ‘Cathedral’ roses. They’re on an automatic irrigation system that puts out plenty of water, three times a week but these roses didn’t put out one new leaf – for months! A little probing into the soil revealed that it was BONE DRY. A tree that was 25 feet away, searching (and finding) water put out a lot of tiny roots and created a nearly impermeable mat above the rose roots preventing water from penetrating the soil. The roses got enough moisture to stay alive, but not to grow. Similarly, a beautiful five year old miniature rose standard in a fifteen gallon pot had been thriving for years. It was hand watered every day, and you could see water running out the bottom of the pot. Once again, after the big spring bloom it dropped all of its leaves and looked horrible! It was nearly dead. That had never happened before. Early in the spring, a new, very vigorous groundcover had been planted in the pot to dress it up; it looked great spilling over the edge. In investigating what was going on with the rose, the groundcover was removed and the ground beneath it was completely dry. The groundcover had diverted the water around to the edge of the pot to run off around the root ball, and absorbed whatever it could. In these cases there was some sort of barrier between the supplied water and the rose roots. Careful planting as well as vigilant observation of your roses performance can prevent this type of drought.
Automated irrigation systems are a real blessing for the roses and the rosarian. But it’s so important to design and install them correctly and confirm that they’re working as intended. Recently, a rosarian in near panic was trying to figure out why the roses in her new home were dying. They’d looked fabulous during the spring, but were now dropping leaves, and in some cases completely dead. The large rose bed had rosemary planted at the base of a number of the plants. It was all on an automated irrigation system. What was killing the roses? Drought – the soil was completely dry around all but a very small area at one point at the base of each plant. Each rose had a single, one-gallon per hour emitter at the base of the rose. The timer was set for daily watering for 15 minutes which calculates to about a quart of water per plant per day in one location. In warm weather, the shallow watering encourages development of surface roots, and rapid evaporation due to high temperatures can deprive the plant of needed water. Ensuring that you have the appropriate number of emitters producing the required volume to deeply water the plant is crucial. It is generally better to water less frequently for a longer duration.
A final example – a large shrub rose that had been producing abundantly for years wasn’t doing a thing a month or so after the rains stopped. It was on an automated system and should have been getting plenty of water. Alas, it was suffering from drought because the spray head was plugged! Sprayers, misters, drip emitters and even distribution lines can get plugged up, and no water gets delivered to your plants. Again, keen observation of your plants performance and diligent maintenance of your irrigation system is key to keeping your roses watered and healthy.