Let’s get one myth over with right now. There are only a very few common perennial flowers that will happily live and tolerate a drought and of these – every one will have reduced blooms in a dry year or the year after.
Perennial flowers are over 90% water. If you reduce the water in the garden, then the first thing a plant will do is conserve water by not producing flowers. And perennial gardens without flowers are so… sad.
This is where water-conserving mulch comes in but the hard reality is that if the soil is dry, the vast majority of perennials will reduce blooms. If you want a perennial garden that looks like the magazines, you have to water.
Some perennials will survive on dry soils – but almost none will thrive in dry soils
Perennial flowers on a well-drained organic soil will require (on average) one-inch to one and a half inches of water every week. I apply my water in two equal watering sessions each week.
Sandy soils (like around new homes or unimproved housing tract soil) will require one and a half to 2-inches a week for best performance. Clay soils are a special case and the gardener with clay will have to do spot trials (stick your finder in the soil to test if it is dry or “almost-dry” and then water accordingly) to determine soil moisture. There is no hard and fast rule for any soil that tends to hold moisture rather than drain it through.
I recommend using measuring cup to ensure you get the right amount of water onto the plants. Gardeners always overestimate how much water they’ve really put on. Put the sprinkler on – time how long it takes to get a half-inch of water into the tub. Now you know how long it takes running your sprinkler systems to apply the amount of water you need.
Ditch the automatic watering systems and timers. They’re more trouble than they’re worth and nothing is funnier than sprinklers running during rainstorms – not to mention how much water you waste.
I find myself switching more and more to drip irrigation. There’s no question you use far less water with drip than overhead sprinklers. This is a good thing if you’re living in a city where you pay for your water or if you live in a drought zone. (I live on the shore of Lake Ontario and have a well that’s fed by that massive body of water)
But still – I’m moving to drip.
Here’s why: With drip, I can water at any time of the day/night. I can get water to plants when they need it. And I lose next to nothing to evaporation no matter what time of day I apply water (overhead sprinklers lose 50% of the water to evaporation with daytime watering)
It’s just as easy to set up and take down drip systems in the fall before winter as it is to remove and store the overhead systems. Both have to be drained and taken in (before the mice decide to feed on them for the heck of it)
I can set up watering zones just as easily but I can water far more of my garden all at once than with overhead. The flow rate of drip irrigation hoses allows me to water quite a few more gardens than with the flow rate of overhead (higher)
I don’t have sprinklers to all parts of my garden, so I have to stop what I’m doing to move sprinklers regularly. With drip, I turn on the tap, and come back a few hours later when things are done. Most of the garden can be watered at the same time.
If you’re mulching your perennial garden, you’re going to have to do finger testing as well. Water levels under mulch are much higher than when the soil is exposed to air and sunlight. It’s a little trickier to get the water right which is why you really need to stick your finger under there.