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Well, we've had every kind of weather this spring and early summer-hot, cold, wet, dry, windy, calm and hot again. The changes have been sudden and sometimes unexpected. All of these fluctuations are stressful for plants in pots, especially those in the open not sheltered by the house walls or eaves. To keep the container plants looking their best, pay attention to their basic needs and try to counteract the effects of downpours and sizzling days.
Remember, a plant in a pot can't search for water the way a ground-planted one can. This means that hot, dry weather can bake the roots very quickly and take the plant past water-stress into the crispy-critter stage in just a few hours. Hanging baskets suffer particularly, because roots fill up the container as the summer progresses. You can't tell if a plant needs moisture unless you check the soil. The best under $10 gadget I own is my water meter. It is a small soil probe that tells me if the soil in a container is wet, moderate or dry. My neighborhood ten year old can use it successfully and look after my plants when I'm away for a week. These are readily available at garden centers and home improvement stores. They are more accurate than the finger-in-the-dirt test, but even method is better than not checking. Soil should feel damp at about one inch down on plants that need steady moisture. Trust me, you can't water well by the calendar and the clock. It's a hands-in-the-dirt job. Getting acquainted with the response of individual planters to water loss will
Containers lose water at different rates. Porous pots like terra cotta dry out quickly and plastic containers stay wet longer. Small pots dry quicker than large ones, except that small plastic pots may stay wetter than medium paper pulp pots. A large wooden tub and a large glazed pot will have different rates of transpiration and need different care, although the bigger the pot the easier it is to manage.
Even more important is the size and number of drainage holes in the bottom of the pot. You must not put a closed, non-draining pot out under the sky in this climate. Get a drill and make some weep-holes in the bottom. You can drill out glass and ceramic if you are careful and use the correct kind of drill bit. On the same note, don't let water collect in the saucers you have put under your pots to catch drips-root rot flourishes when soggy saucers hold too much extra water. Better yet, eliminate the saucers altogether. Raising containers off deck levels with small bricks works well. Move everything now and then to allow the deck to dry completely.
To add to what the gardener must watch, different plants need different levels of moisture to thrive. The succulents, cacti and other xeric plants, need much less water generally and will soon rot if their pots are kept too wet. They may suffer if left to the mercies of Western Washington's drizzly summers. The ones that can't take soggy conditions should be placed under the eaves or on a porch where the vagaries of Mother Nature can't reach them.
Most commonly grown potted plants, like the summer annuals, want an even supply of moisture-not too dry and not too wet. They can usually tolerate some fluctuations and that's why they are so easy to grow and so popular. But even the old standbys like petunias and marigolds can die from over or under watering. I try to keep plants with similar requirements together when I'm planting a mixed pot and group the thirsty pots to simplify my routine when I'm watering in a hurry.
A drip system with a timer can be wonderful for permanent containers. It doesn't work as well if you are constantly moving the pots around, like I do, but it might be just the thing for your garden, especially if there's someone on hand with an engineering inclination.
A plant that is actively growing needs more water than when resting or dormant.
So, after you have planted little seedlings into your troughs, they need a steady
supply of water until they have reached full flowering size. Then their growth
slows while they make flowers and seeds. But, if they get too dry, they will
stop flowering and die prematurely. It's all a question of balance. Nature is
not giving us predictable and rational weather this year. We have to work at
correcting the overdoses and shortages that the sky provides. It's a challenge
and a daily chore, but I won't part with any of my 47 containers-each one is
a small, decorative jewel in my landscape.
Hortsense: Managing plant problems with Integrated Pest Management
