Well, we got through the worst of the heat wave but just barely for some plants and critters. Now we're back to the familiar mid-nineties and high humidity that we here in Columbia have all come to know and love.
I wrote to you last week about watering during this heat wave and have pasted in that note below. I want to add something here about irrigation systems and shrubs. I have noticed a tendency folks have pretty much everywhere to irrigate too often and not deep enough. Irrigating too often may cause the ground to be damp more often than it should be, inviting fungal diseases. Irrigating too shallowly does not allow water to get to the deeper roots, and also trains the plant roots to stay on the surface to grab water before it evaporates. What I have just written is true of lawn irrigation, but is even more true regarding the irrigation of shrubs and perennials and trees. Generally I would say irrigate less often and for a longer time period (more deeply). Try to avoid irrigating in the late afternoon since this will keep the ground moist all evening promoting fungus growth. For those who have a timed drip irrigation system in their beds, I would also suggest irrigating more deeply and less often. Mulch really helps water retention of course.
Speaking of mulch, this is one time of year when it is especially needed.
This time of year is one of strong growth in plants. It is a venus-fly-trap eat venus-fly-trap world out there, and plants are trying to make as much food as they can, which also means that they are devoting some of that energy to making even more leaves for making even more food. More leaves means more transpiration which increases demand for soil water, so on and so forth. After summer flowering, plants start to divert a lot more energy to formation of fruits and seeds. Some times it is best to pick off fruits - such as camellia - so as to divert more energy into the growth and development of buds - next seasons flowers and leaves. For common non native cultivated plants that continually bloom (like knock out roses) there is a greater demand for nitrogen, which means there is a need for fertilizer. But fertilizer (a kind of salt) requires a lot more water, so unless you are going to be very very diligent about watering this is not a great time to fertilize.
Why is this? Remember that thing called osmosis you learned about in high school? Water is always wanting to spread solute happiness around as evenly as possible by having equal concentrations of dissolved solutes (such as dissolved salts or ions) everywhere. So if two bodies of water are separated by a semipermeable membrane (across which water can flow but not the stuff dissolved in it), the water will move from the side that has a lower concentration of dissolved solutes to the side with a higher concentration, thus equalizing the concentrations. So, if the water around the root hairs of a plant has a high concentration of dissolved solutes like fertilizer, it can actually cause water to flow FROM the root out to the soil to equalize these concentrations. This is not cool for the plant, especially in the summer when so much water leaving the leaves and demand for water is up. (For those interested osmosis is a variation of the law of entropy - but that is for another day.)
The moral of the story is that unless you want to water a lot - and you may well want to if want to produce a bumper crop of knock out rose blossoms in mid summer - you may just wait to fertilize.
This is of course not a great time to transplant either. But it is OK to plant from container to soil IF you are diligent in watering.
There are exceptions to this planting rule. Right now is a very good time to dig and divide and replant Iris for example. If your lily leaves are turning brown this means that they are not producing food for the bulbs, so if you need to dig and divide lilies you can do that now too.
Since you are almost certainly already watering annuals regularly you can fertilize them, and...I like this...you can still sow seeds for some of my most favorite annuals for fall color - such as zinnias (I love zinnias).
It is hot out there, and thankfully after this Sunday we also have water! So guess what is growing like crazy - WEEDS!. I know, it is terrible to do plant profiling, but some plants are genetically designed to grow and propagate like crazy in disturbed soils (i.e., gardens). That's their biological niche and they aim to be first out of the chute, or dirt. Many species of weeds propagate by seed only - such as "mimosa weed" and crabgrass. It is very helpful not to let them go to seed. Some weeds need to be yanked out root and all. Either way, the weeds are likely growing faster than you can keep up!
Speaking of crazy growth, this is the time for vines and saplings to take off. By now wisteria, virginia creeper, trumpet vine, cross vine, akebia, bramble, ivy, vinca, honeysuckle, smilax, kudzu, and a dozen other vines are starting to swamp, strangle and block the sun from your plants. Saplings of cherry laurel, sweet gum, hackberry, and oak are popping up and getting established everywhere. July is actually a VERY GOOD time for cleaning out jungly growth from shrubs, flower beds and trees. I would love to dejunglfy your place this summer. So let me know...It is actually possible to eradicate almost all these vines. And remember, they are competing with your shrubs not only for light (as they swallow them up), but also for water and nutrients
As to pruning, it is still hydrangea pruning time - the regular big leafed hydrangea and our wonderful native oak leaf hydrangea. There is really no super great way to prune hydrangeas, but the time to do so is soon after they bloom since they set buds for the next season on this season's new growth. When hydrangeas get big and haggard looking it is good to cut about a third of the stems down to the ground. This seems to have a stimulating effect on the overall growth. It is best to do this with the tallest or most bent or oddly shaped shoots. It's not a great idea to clip back everything a foot or whatever...new growth will send out shoots from the cut area and produce lots of flower buds, and then the next season the whole plant will be top heavy. I guess it is much of an art than a science pruning these guys. As to oak leafs, it is best not to prune them at all - BUT, as I have seen first hand recently, oak leaf hydrangeas can get very large, and the shoots so heavy with blooms that they just fall over, crack, and often die. That's the time for a pruning...
Lots of shrubs can be pruned or cut back now as long as new growth for bud production isn't needed. Camellias for example...Many camellias have too many branches and need to be thinned out. Some need to have bottom limbs removed since camellia limbs on the ground promotes camellia blight. Some camellias look better "legged up." All this can be done now. Many shrubs not known for blossoms can be pruned and cut back about as well now as any other time.
Did I say it was a good time to mulch?
Well, this should do...below is the text from the brief note I sent out last week about watering...
Stay cool and have a great 4th of July.
Dear Gardening Friends,
Well, the forecast for the next few weeks is pretty crazy in terms of heat and absence of rain. Just wanted to put out a note about watering, and a word on behalf of my feathered friends.
A lot of plants will be highly stressed over the next few months. Deep hand watering of anything planted or transplanted in the last year would be a good idea, or for that matter any non native plant in dry sunny corners of your yard. If you are going to be away and would like for me to stop by and do some watering, I can do that.
Also, this will be a very very tough period for birds. They will be parched, and for any birds raising a second brood of little ones, or mating and laying eggs late, it is a very tough time for the little guys. Water is good - very good. Even if you don't have a bird bath you can let the hose run around a plant that needs watering and the birds will find it and be splashing around in no time.
I know some of you worry about me working in the heat, and I appreciate that. I will be working as usual - though I will be taking more precautions - a better hat, a cooler with ice, and as I tend to do in the summer, I will be following the shade. I also hope to start working earlier. I typically find the heavy humid dead air of the morning to be worse than the heat later in the day, but this heat will be worse than usual.
This is of course not a great time to plant - especially in a sunny location (though as long as one waters regularly it is normally OK to plant in the summer), but it is a good time to clear out beds, get rid of vines and ivy and unwanted trees and so forth. And it is still barely OK to prune azaleas and still have blooms for next year if you do that in the next week or so.
I got a couple of cool gardening books for Father's Day one of which is entitled Gardens and Historic Plants of the Antebellum South. I have also been reading William Bartram's Travels through North and South Carolina, Georgia, East and West Florida(short title). I hope to be sharing insights and reflections inspired by these works over the course of the summer. I am pretty focused on learning more and more and am beginning a process of being able to do better design work as well.
Well, hang in there and be safe!