Friday, 24 May 2013
Asparagus is an interesting and unusual vegetable to grow. Unlike most veggies, which are grown as annuals, it's a perennial. Once planted, it takes several years to get large and strong enough to harvest, but then will be there to harvest every year for 20 to 30 years or more. The sight of them in the spring is amazing. They look just like asparagus... coming right out of the ground! If you don't pick the stalks, they quickly shoot up and open to a large, ferny plant that is the general shape of a pine tree, but more airy. Well-established plants can easily reach 6 or 8 feet in height, and the stalks can be quite tough and woody when you clear them away in the fall.
Most people buy asparagus plants (sold as "crowns") when they plant it. You can buy one year old or two year old crowns; the two year old will be more expensive but theoretically ready to harvest a year sooner. I say theoretically, because in my experience larger plants take longer to settle in and smaller plants are likely to catch up. Don't really expect to pick much asparagus until the third year anyway.
You can also grow asparagus from seed. Asparagus is easy to start from seed, since the seeds are large, and germinate readily at warm temperatures. Start them indoors fairly early in the season, say sometime in March, to give them the longest start their first season, but you could start them as late as June and expect most of them to survive the winter. Plant them out once danger of frost has finished. (Which at the rate we are going here, might be next year some time. Argh.) This will be considerably less expensive than starting with crowns, but you will need to add at least another year to the waiting time. What we did was plant some of both, to allow us some earlier asparagus but still save some money.
Asparagus likes good rich soil, and it will be in place for a long, long time, so choose your planting site carefully. It needs full sun, and should not have to compete with tree roots. It's worth while to expend some effort in improving the bed with compost and a little bonemeal. It's even more worth while to be sure the bed is really, really free of weeds before you plant. Since asparagus also likes a moist but well drained soil - it can actually be quite dry once the first flush of growth is past in the spring - it's best to raise the bed a little. It also prefers slightly alkaline soil, although ours has tolerated our slightly acidic soil very well. The moisture level is more important; the fact that our soil is quite sandy helps a lot.
Once you are ready to plant, the asparagus goes in quite deeply. Since your plants will start out as miniature versions of their more mature selves, it's best to dig a bit of trench to start them off in, and fill it in as they get to look more robust. Ultimately, they should end up about 8" deep. Deep plantings will help encourage thick, fat spears - much more succulent than skinny ones. Once you are getting fairly thick spears, you will know they are mature enough to harvest. Start by harvesting for 2 weeks the first year, checking the bed every day or two for new growth, and work up to 6 weeks of harvesting once the beds are completely mature. (Some people say 8 weeks, but that just seems so long to me. Poor plants!) The plants should be spaced about a foot apart in any direction; your choice whether to plant them in a bed or a row. Don't make your bed too wide though! Five feet is probably the maximum; four is better if you don't have long reach, as you should stay out of the bed to avoid compaction and breakage.
Asparagus does not have many pests or diseases. Ours is afflicted with both striped and spotted asparagus beetles, which are by far the most common pests of asparagus. They are distinctly a nuisance, and we try to control them with hand-picking and insecticidal soap, but they persist nevertheless. Fortunately, they don't seem to do a lot of harm, since they don't really get going until after we stop picking and the plants will put out new growth to replace what has been eaten. We remove the dead ferns at once in the fall, in the hopes of removing some of the eggs as well. This is generally a good practise, although some people wait until very early spring to remove the debris. Either way, it should be removed, to help prevent the build up of fungi or beetles. Rust (a fungus) is another problem that may affect asparagus, but modern varieties are fairly resistant to it. Aphids may also show up, in season, but again are probably more of a nuisance than a danger.
It's important to keep your asparagus well weeded. Once deep-rooted weeds get into it, it is next to impossible to get them out again. The previous owners planted our first patch of asparagus, then let it go to weeds. We are still, 5 years later, fighting those weeds constantly. I'm told that you can water your asparagus with salt water to kill weeds, since asparagus was originally a seaside plant and is very salt tolerant. I have not had the nerve to try this, as I worry about run-off affecting other plants.
One experiment we have tried is planting strawberries amongst the asparagus. Our hope was that since asparagus is deep rooted, and strawberries are shallow rooted, that the strawberries would smother the weeds and give us a double crop. The results have been mixed. If you are short of space, it works quite well for double cropping. Strawberries don't mind the light shade provided by the asparagus and the roots don't seem to compete too much. However, strawberries really aren't that great at keeping down the weeds. Any time saved by their taking up the space of some of the weeds is lost by the fact that you have to weed around them. They also make it a bit difficult to mulch or to fertilize the asparagus. If you don't do this, it makes a lot of sense to mulch. Grass clipping work well, provided they are cut before the grass goes to seed, and are likely to be readily available.
As you may suppose, a perennial plant can't have all its growth cut for 6 weeks or more every spring without needing a lot of fertilizer to help it keep going. We are still working out a good plan, but the recommendation is to fertilize your beds twice per year. Once right after you stop cutting for the season, and once in the late fall or early spring. My thinking is that it may be best to use a little bone and bloodmeal in the early summer once you stop picking, along with a foliar feed of kelp based fertilizer, with a good 2" mulch of compost or old manure in the late fall or very early spring. I prefer the fall to the spring, because then it has the winter to really work its way into the soil.
How much asparagus should you plant? I've seen recommendations of 5 plants per person right up to 30 plants per person, with 10 being a fairly typical recommendation. It depends on how much you love asparagus and of course how much space you have to allot to it. We could eat a good half pound of it each, every day, in season so have gone for the high end figure. We don't bother to freeze it. I don't think frozen is nearly as good as fresh, and I find its fleeting nature is part of the pleasure of asparagus. Another thing that will affect how many plants you need is whether they are male or female plants... oh yeah, asparagus has the MOST interesting sex life. I had no idea.
It's a little unusual, but not particularly rare, for plants to have separate male and female flowers or even separate plants, as asparagus does. Asparagus is a dioecious plant. What this means is that if you want seeds, you must have some male and some female plants to get fertile berries on the females. Unless you are a breeder, however, you are most unlikely to want to get berries, and there are real disadvantages to growing female asparagus plants. They grow fewer spears, so about half harvest in the same space as a male, and furthermore the spotted asparagus beetle particularly likes to feed on the berries and lay eggs in them, so better not to have them. Male plants are also up earlier in the spring, and live longer too.
How do you get male plants only? This is where things go from the slightly unusual to the whoa, really!?! Traditional varieties will produce about half and half male and female plants when grown from seed, and even if you plant crowns, they will have been grown from seeds originally, so you can expect that half of your crowns will be female. You can dig out female plants and replace them new crowns once they are mature enough to identify, but you will still be replacing them with half female plants. You can improve the situation considerably by doing this, but it might be easier to simply plant one of the all-male hybrids to start with.
When I first heard of all-male hybrids, my first question was, "HOW THE HELL DO THEY DO THAT?" and the answer is fascinating: they use super-males. Yes, asparagus has three sexes: female (xx chromosomes), male (xy chromosomes) and super-male (yy chromosomes). If you cross a super-male (yy) with a female (xx) asparagus, the resulting offspring should always be males (xy). Voila; all-male seed. It's a bit more complicated than that in real life, and you may get the occasional female plant from "all"-male hybrids, but it's close enough to go on with.
So, it's time to talk about specific varieties of asparagus. They all taste pretty similar, so the actual variety will be of more interest to the gardener than the cook. Asparagus is available in three colours; the original green, purple-tinted, and white. White is just a green asparagus that has been earthed up as it grows to prevent the formation of chlorophyll, so it's a technique rather than a specific variety. I don't care for it and couldn't be bovvered anyway, so no info about doing that here.
The most common traditional varieties of asparagus around here seem to be Mary Washington, Argenteuil, Mary Washington, Viking, Mary Washington, and Mary Washington. Yeah. Odds are very good that you are going to get Mary Washington.
Purple asparagus is a lot less common, and there only seem to be a few varieties, none of which appear to be all-male at this point. Purple Passion is the most common, but we got our hands on some Crimson Pacific seed this spring and will be trying it out. Purple asparagus is supposed to be sweeter than green asparagus. Alas; it turns green when cooked.
The most common all-male hybrid around here is Guelph Millennium, bred at the University of Guelph. You can expect to pay about ten times the price for seed as for the old standards, and I haven't seen it available as crowns (yet). Apparently there are a good few out of New Jersey as well; Jersey Giant, Jersey Knight, and Jersey Supreme. Given the investment in time into asparagus, if you are growing it from seed the extra money spent is probably well worthwhile. Ordinarily, I try to avoid F1 hybrids, but with asparagus the difference is so real and the plants so long-lived there is no reason not to go for them.