For those of you in the Seattle area, now's the time to really start watching your soil moisture levels. It seems like we're getting rain, but its tapering off & soil water moisture levels are getting more shallow. Here are some tips to understand soil moisture & how to effectively maintain it:
Watering the garden is one of the hardest gardening arts to master. You will want to be sure you are watering enough so that the area around the plants’ root zones remains moist but not saturated. Many components go into correct watering such as temperature, exposure, types of plants, type of soil, and so forth. Without getting too complicated, go into the garden and dig down around 12”. If you do this today, after a the recent rain we've had, you should find the soil is moist but not soggy. (This can vary depending on how much rain you've gotten, your soil type, exposure, etc...) This is essentially what you will want to maintain – moisture in the first 12”-18” of soil. Now, how do you keep this moisture balance going?
For your mixed shrub & perennial beds, I suggest you try watering the entire area for 15-25 minutes in the morning. (Early morning is ideal, but evening is also acceptable. Mid-day is wasteful.) Then wait about 1 hour and do your 12” dig test. Is the soil moist down in the root zone area? If not, you can repeat the 15-25 minute watering & test again in 1 hour. Repeat as needed. What you are doing is wetting the soil & giving it time to percolate down into the soil profile, making it available to roots. If you keep the soil moist in that root zone area, you will end up needing to water less as you will be watering more efficiently. Through the summer, if you water this way, you should only need to water every few days. And, after a while, you won’t need to do the 15 minute, 1 hour test & repeat. You’ll start to get a feel for how many times you’ll need to run the water and for how long to keep your garden water table balanced.
If we have rains in the summer in Seattle, they tend to be fairly sporadic and often don’t provide what plants really need. These rains are deceiving! Plus, we have a natural drougth cycle that will really kick in right after the 4th of July.
If we have a day of all-day downpour, your garden should be fine for a few days (assuming you've keep that moisture depth going strong). Just check the soil moisture level a couple of days after the downpour & then water as needed. If we have grey days with a few sprinkles, these days won’t contribute much to your plants’ soil moisture needs. However, they will keep the ground from drying out as fast as a hot, sunny day will cause.
If you plan to mulch over your weeded beds, this will help reduce the amount of water required and will help deter weed growth. The organic matter in mulch has a high water-holding capacity so it will hold the water longer than some soil types, cooling roots. (Note: clay has high water holding capacity; sand has low capacity. Don't think you have clay simply because your soil is hard to dig in. Soil texture & structure is another topic for another day.)
Before you mulch your beds, be sure to water the beds really well so the soil is moist in the root zones. Then top dress the beds with 2”-4” of mulch & water again. This will balance out the water throughout the soil profile. If you mulch over soil that isn’t moist & then begin watering, the mulch will hold the water tightly & it won’t make it down to the plants’ roots.
When selecting a mulch, avoid beauty bark products. This can be a longer topic, but know that beauty bark is notorious as a disease carrier and is made of tree bark. Tree bark contains cutin, which is a waxy substanced that wicks water away.
